**4.1.2 Methodology**

50 Earthquake Research and Analysis – Statistical Studies, Observations and Planning

aggregation in 0.1-bins is small, it influences the *b*-values weakly and uniformly; therefore it was not taken into account. The maximum likelihood method (3) gives a suitable *b*-value estimation for a number of events exceeding 50. Having this in mind the groups consisting of 50 subsequent events were used in *b*-value determination. The data points in Fig. 3 reflect the *b*-values obtained for such groups with step 25 events; thus the data points are

As it can be seen in Fig. 3, there is an evident tendency of decrease in *b*-values in the time vicinity of the generalized main shock; and this decrease increases strongly with approaching the moment of the main shock. In the foreshock sequence the noticeable decrease begins about one hundred days before the main shock. In the aftershock sequence the sharp increase in *b*-values takes place during the first several days after the main shock. A slow increase in *b*-values takes place in the following 100 days. It is necessary to notice that the *b*-values appear to be increased in comparison with the background value in the time interval 10-100 days after the main shock occurrence. These features agree with a tendency of lowermost *b*-values in the very beginning of the aftershock sequences and with an increase of *b*-value in the further evolution of the aftershock sequences (Rodkin, 2008; Smirnov & Ponomarev, 2004). The similar tendency was found in the examination of acoustic emission data (Smirnov & Ponomarev, 2004). New findings consist in the stronger decrease than it was found before and in rather symmetrical character of this decrease for fore- and aftershock sequences. Note that the amplitude of the *b*-value decrease appears to be proportional to the logarithm of time remaining from the moment of the main shock.

Note however that the well known and widely used below effect of "seismic quiescence" was not found in the generalized vicinity of strong earthquake. It can be connected with anisotropic character of this type of precursor anomaly in relation to a strong earthquake epicenter that is mentioned in (Zavyalov, 2006). In this case this effect can be eliminated by summarizing data from vicinities of a large number of differently oriented strong earthquakes.

Region under study includes the Sakhalin Island and the Kuril Islands arc. In a few cases the area of the Japan Islands was also taken into account. This territory belongs to the transitive zone between the Pacific and the Eurasian continent and includes the active island arc characterized by one of the highest levels of seismicity on the Earth. Because of variability in quality of available catalogs the methodology of prognosis is more or less different in every

To avoid misunderstanding and controversial interpretations, we follow below the definition of the term "earthquake prediction," which was formulated by the Panel on

"An earthquake prediction must specify the expected magnitude range, the geographical area within which it will occur, and the time interval within which it will happen with sufficient precision so that the ultimate success or failure of the prediction can readily be judged. Only by careful recording and analysis of failures as well as successes can the eventual success of the total effort be evaluated and future directions charted. Moreover,

Earthquake Prediction with the US National Academy of Sciences (Allen et al., 1976):

**4. Experience in earthquake prediction at the Sakhalin Island and** 

particular case of strong earthquake prognosis, which is described below.

independent of those next to the adjacent ones.

Such type of behavior is typical of critical processes.

**surrounding areas** 

The intermediate-term earthquake prediction technique, named M8 algorithm, is based on an assumption that a number of functions, defined for a particular earthquake sequence, become extremely large in values, within several months prior to a major shock. The functions used are following (Keilis-Borok & Kossobokov, 1986, 1990):

N – cumulative number of main shocks (aftershocks are excluded according to (Keilis-Borok et al., 1980)) describes an increase in seismic activity;


All functions, except the last one, were calculated twice: for a standard variant of small statistics (10 events or less per year) and for a standard variant of large statistics (20 events or more per year); where the numbers of events change by choice of threshold of magnitude taken into account. Two statistics are used for increasing robustness of results of prognosis. Values of these seven functions were used for adjusting the M8 algorithm, and then for diagnostics of Time of Increased Probability (TIP) for large earthquake (M ≥ 7.5) occurrence within the circular areas with a fixed radius.

Besides the method described above, we used a visualization technique to display spacetime distribution of seismicity to detect seismic gaps of the second kind. A gap of the second kind (seismic quiescence) refers here to a portion of a seismic area of low seismic activity with no observed earthquakes with М≥6.0 for a period of several years. This approach follows the concept of K. Mogi (1985).

Current State of Art in Earthquake Prediction, Typical Precursors and

suggest that in case 1 the term "prediction" is suitable.

**4.1.4 Realization of prediction** 

seismic gap of the second kind.

every six months.

Experience in Earthquake Forecasting at Sakhalin Island and Surrounding Areas 53

the Southern and Northern Kuril Islands. The catalog data have been processed by the M8 algorithm for the time period from 1962 to July 1992, with the functions being calculated for

Some results of the processing are presented in Fig. 4, which demonstrates the behavior of all seven functions in the first circular area (Southern Kuril Islands) during the diagnostics period (1979-1992). All the functions have become extremely anomalous, large in values to the July of 1992, which means, that the M8 algorithm diagnoses the TIP for a large earthquake occurrence during next 5 years (1993-1997). The alarm should be kept if

The similar results have been derived by the authors of the M8 algorithm on the base of processing of the NEIC/USGS catalog data (Kossobokov et al., 1994, 1996). All needed parameters of the prognosis of the future strong earthquake were indicated, and thus we

For the second circular area (Northern Kuril Islands) anomalous value has been obtained for the B function (bursts of aftershocks) only, and it means, that M8 algorithm diagnoses no

The above mentioned suggested a high probability of occurrence of large earthquake within the Southern Kuril zone in the nearest years. This suggestion was found to be in an agreement with the space-time distribution of earthquakes with M ≥ 6.0 within the Kuril seismic zone since 1987 (Fig. 5). A large seismic gap of the second kind can be seen within a big area from the southern part of Urup Island to the northern end of Hokkaido Island.

The prediction described above was submitted in July of 1992 to the Russian Academy of Sciences and the Ministry of Emergency Situations (REC RAS/EmerCom). It was written in the conclusion that "the Southern Kuril region and the area to the east of Hokkaido Island will remain in a state of high probability of a large (M=7.5-8.5) earthquake occurrence during 5 years, which started since the middle of 1992" (Kossobokov et al., 1994, 1996).

Fig. 5. The distribution of epicenters of earthquakes with M ≥ 6.0 in the Kuril-Hokkaido area for the period from March 1987 to July 1992. The area limited by solid lines is the area

anomalous values of almost all the functions are kept in the next six months.

TIP for a large earthquake occurrence in this area within the next 5 years.

#### **4.1.3 Results of analysis and precursors phenomena**

Seismicity of circular areas with a radius of 427 km with the centers located in the points: 440 N, 1490 E; and 480 N, 1550 E has been examined. These two circles overlap all the territory of

Fig. 4. The behavior in time of seven functions of the M8 algorithm for the Southern Kuril region during the diagnostics period, 1979-1992. The solid lines show the values, calculated for large statistics (20 events or more per year), and the dash lines show the values for small statistics (10 events or less per year). Star symbols mark anomalous values.

the Southern and Northern Kuril Islands. The catalog data have been processed by the M8 algorithm for the time period from 1962 to July 1992, with the functions being calculated for every six months.

Some results of the processing are presented in Fig. 4, which demonstrates the behavior of all seven functions in the first circular area (Southern Kuril Islands) during the diagnostics period (1979-1992). All the functions have become extremely anomalous, large in values to the July of 1992, which means, that the M8 algorithm diagnoses the TIP for a large earthquake occurrence during next 5 years (1993-1997). The alarm should be kept if anomalous values of almost all the functions are kept in the next six months.

The similar results have been derived by the authors of the M8 algorithm on the base of processing of the NEIC/USGS catalog data (Kossobokov et al., 1994, 1996). All needed parameters of the prognosis of the future strong earthquake were indicated, and thus we suggest that in case 1 the term "prediction" is suitable.

For the second circular area (Northern Kuril Islands) anomalous value has been obtained for the B function (bursts of aftershocks) only, and it means, that M8 algorithm diagnoses no TIP for a large earthquake occurrence in this area within the next 5 years.

The above mentioned suggested a high probability of occurrence of large earthquake within the Southern Kuril zone in the nearest years. This suggestion was found to be in an agreement with the space-time distribution of earthquakes with M ≥ 6.0 within the Kuril seismic zone since 1987 (Fig. 5). A large seismic gap of the second kind can be seen within a big area from the southern part of Urup Island to the northern end of Hokkaido Island.

### **4.1.4 Realization of prediction**

52 Earthquake Research and Analysis – Statistical Studies, Observations and Planning

Seismicity of circular areas with a radius of 427 km with the centers located in the points: 440 N, 1490 E; and 480 N, 1550 E has been examined. These two circles overlap all the territory of

Fig. 4. The behavior in time of seven functions of the M8 algorithm for the Southern Kuril region during the diagnostics period, 1979-1992. The solid lines show the values, calculated for large statistics (20 events or more per year), and the dash lines show the values for small

statistics (10 events or less per year). Star symbols mark anomalous values.

**4.1.3 Results of analysis and precursors phenomena** 

The prediction described above was submitted in July of 1992 to the Russian Academy of Sciences and the Ministry of Emergency Situations (REC RAS/EmerCom). It was written in the conclusion that "the Southern Kuril region and the area to the east of Hokkaido Island will remain in a state of high probability of a large (M=7.5-8.5) earthquake occurrence during 5 years, which started since the middle of 1992" (Kossobokov et al., 1994, 1996).

Fig. 5. The distribution of epicenters of earthquakes with M ≥ 6.0 in the Kuril-Hokkaido area for the period from March 1987 to July 1992. The area limited by solid lines is the area seismic gap of the second kind.

Current State of Art in Earthquake Prediction, Typical Precursors and

Experience in Earthquake Forecasting at Sakhalin Island and Surrounding Areas 55

Fig. 7. The cumulative number of earthquakes observed by USGS/NEIC in the Southern

**4.2 Case 2 - Partly retrospective forecasting of the May 27, 1995 Mw 7.1 Neftegorsk** 

Seismicity of the northern part of the Sakhalin region (north of latitude 500 N) was the object of this investigation. It had a moderate level of seismicity in comparison with seismic activity of the Kuril Islands. Destructive earthquakes like the 1995 Mw 7.1 Neftegorsk earthquake are rare events here. Paleoseismological reconstruction within the Upper Piltun fault, which was reactivated during the Neftegorsk earthquake, showed that recurrence of such earthquake is about one event per several hundred years (Shimamoto et al., 1996). Seismicity patterns were analyzed on the basis of the regional catalog of shallow-focus M

In this case same methods as in the case of the Shikotan earthquake were used. A magnitude for identification of a seismic quiescence area for the Sakhalin region was taken M = 3.0.

The second kind seismic gap area taking place along the eastern coast of the Northern Sakhalin has indicated the approximate location of a possible future large earthquake (Fig. 8) (Kim, 1989). The gap of the second kind was recognized in 1989, i.e. 6 years before the Neftegorsk earthquake, it was outlined in the area of 200 by 60 km including the shelf and coastal areas from the southern part of the Shmidt Peninsula to the Gulf of Chaivo. There

The stair-case curve is empirical data, and the smooth curve simulates the data according to the method of self-developing processes. The vertical line is the asymptote corresponding to

Kuril Islands area as a function of time through April 1993–November 1994.

3.0 earthquakes, issued by ESSN (The earthquakes in USSR…, 1964-1991).

**earthquake, North-Eastern part of Sakhalin Island, Russia** 

**4.2.3 Results of analysis and precursors phenomena** 

were no earthquakes with M ≥ 3 in this area since 1984.

**4.2.1 Seismic region and data** 

**4.2.2 Methodology** 

the prognostic event date three days after the earthquake occurrence (the arrow).

A large Mw 8.3 shallow-focus (h ~ 40 km) earthquake has occurred on 04 October 1994 at 13:22 GMT to the east of Shikotan Island (Russia) (Fig. 6). Thus, the intermediate-term prediction of July 1992 was confirmed.

Fig. 6. Epicenters of the 1994, Mw 8.3 Shikotan earthquake and first-day aftershocks of magnitude M ≥ 5.0.

Just before the Mw 8.3 Shikotan earthquake the seismic stations in Kurilsk and at Shikotan Island were closed because of the economic crisis. In this situation we have no data to attempt to perform a short-term prognosis. But using a posteriori data from USGS/NEIC a short-term prognosis of this event was done. We used the method of self-developing processes, which was suggested by Malyshev (Malyshev, 1991; Malyshev et al., 1992). It is described below (case 4) where it was applied in a real time. By the use of this method the one and a half year foreshock sequence of events was analyzed and the date of the strong earthquake occurrence was a posteriori estimated with a few days delay (Fig. 7).

#### **4.1.5 Case 1 summary**

Some characteristics of the earthquake flux for the period from 1962 to July 1992 in the Kuril seismic zone have been investigated on the basis of two methods: (1) the intermediate-term earthquake prediction algorithm M8; (2) a visualization of space-time distribution of seismicity. The M8 algorithm diagnosed the Time of Increased Probability for a large earthquake occurrence in the circular area with the radius of 427 km at the point (440 N, 1490 E) during the period 1993-1997. By means of the second method the seismic gap of the second kind was detected within a big area from the southern part of Urup Island to the northern end of Hokkaido Island. The quiescence began in March 1987. A catastrophic shallow-focus (h ~ 40 km) Mw 8.3 earthquake has occurred on 04 October 1994 at 13:22 GMT to the east of Shikotan Island (Russia).

A posteriori short-term prognosis by the method of self-developing processes data was performed using USGS/NEIC data. The date of the strong earthquake occurrence was a posteriori estimated with a few days delay (Fig. 7).

Fig. 7. The cumulative number of earthquakes observed by USGS/NEIC in the Southern Kuril Islands area as a function of time through April 1993–November 1994.

The stair-case curve is empirical data, and the smooth curve simulates the data according to the method of self-developing processes. The vertical line is the asymptote corresponding to the prognostic event date three days after the earthquake occurrence (the arrow).

#### **4.2 Case 2 - Partly retrospective forecasting of the May 27, 1995 Mw 7.1 Neftegorsk earthquake, North-Eastern part of Sakhalin Island, Russia 4.2.1 Seismic region and data**

Seismicity of the northern part of the Sakhalin region (north of latitude 500 N) was the object of this investigation. It had a moderate level of seismicity in comparison with seismic activity of the Kuril Islands. Destructive earthquakes like the 1995 Mw 7.1 Neftegorsk earthquake are rare events here. Paleoseismological reconstruction within the Upper Piltun fault, which was reactivated during the Neftegorsk earthquake, showed that recurrence of such earthquake is about one event per several hundred years (Shimamoto et al., 1996). Seismicity patterns were analyzed on the basis of the regional catalog of shallow-focus M 3.0 earthquakes, issued by ESSN (The earthquakes in USSR…, 1964-1991).

#### **4.2.2 Methodology**

54 Earthquake Research and Analysis – Statistical Studies, Observations and Planning

A large Mw 8.3 shallow-focus (h ~ 40 km) earthquake has occurred on 04 October 1994 at 13:22 GMT to the east of Shikotan Island (Russia) (Fig. 6). Thus, the intermediate-term

Fig. 6. Epicenters of the 1994, Mw 8.3 Shikotan earthquake and first-day aftershocks of

earthquake occurrence was a posteriori estimated with a few days delay (Fig. 7).

Just before the Mw 8.3 Shikotan earthquake the seismic stations in Kurilsk and at Shikotan Island were closed because of the economic crisis. In this situation we have no data to attempt to perform a short-term prognosis. But using a posteriori data from USGS/NEIC a short-term prognosis of this event was done. We used the method of self-developing processes, which was suggested by Malyshev (Malyshev, 1991; Malyshev et al., 1992). It is described below (case 4) where it was applied in a real time. By the use of this method the one and a half year foreshock sequence of events was analyzed and the date of the strong

Some characteristics of the earthquake flux for the period from 1962 to July 1992 in the Kuril seismic zone have been investigated on the basis of two methods: (1) the intermediate-term earthquake prediction algorithm M8; (2) a visualization of space-time distribution of seismicity. The M8 algorithm diagnosed the Time of Increased Probability for a large earthquake occurrence in the circular area with the radius of 427 km at the point (440 N, 1490 E) during the period 1993-1997. By means of the second method the seismic gap of the second kind was detected within a big area from the southern part of Urup Island to the northern end of Hokkaido Island. The quiescence began in March 1987. A catastrophic shallow-focus (h ~ 40 km) Mw 8.3 earthquake has occurred on 04 October 1994 at 13:22 GMT to the east of

A posteriori short-term prognosis by the method of self-developing processes data was performed using USGS/NEIC data. The date of the strong earthquake occurrence was a

prediction of July 1992 was confirmed.

magnitude M ≥ 5.0.

**4.1.5 Case 1 summary** 

Shikotan Island (Russia).

posteriori estimated with a few days delay (Fig. 7).

In this case same methods as in the case of the Shikotan earthquake were used. A magnitude for identification of a seismic quiescence area for the Sakhalin region was taken M = 3.0.

### **4.2.3 Results of analysis and precursors phenomena**

The second kind seismic gap area taking place along the eastern coast of the Northern Sakhalin has indicated the approximate location of a possible future large earthquake (Fig. 8) (Kim, 1989). The gap of the second kind was recognized in 1989, i.e. 6 years before the Neftegorsk earthquake, it was outlined in the area of 200 by 60 km including the shelf and coastal areas from the southern part of the Shmidt Peninsula to the Gulf of Chaivo. There were no earthquakes with M ≥ 3 in this area since 1984.

Current State of Art in Earthquake Prediction, Typical Precursors and

demonstrated an ability to recognize the danger.

earthquake (Fig. 10).

Experience in Earthquake Forecasting at Sakhalin Island and Surrounding Areas 57

regional catalog (Keilis-Borok et al., 1980). The M8 algorithm was adjusted to the earthquake

In this case data processing was performed under a strong shortage of data (only 4-5 events per year). Dr. Kossobokov analyzed two cases in the similar poor data conditions for the use of the M8 algorithm - deep earthquakes of the Vrancha region (Kossobokov, 1986) and seismicity in Greece (Latoussakis & Kossobokov, 1990). In the first case small and "large" statistics was equal to 2 and 4 events per year but in the second case it was equal to 5 and 10 events per year. However, even under such unfavorable conditions the M8 algorithm has

In our case only one dangerous period was revealed a posteriori since 1991 when six functions became anomalous (B function was undefined because of poor statistics of small earthquakes). The alarm period was interrupted by the May 27, 1995 Mw 7.1 Neftegorsk

Fig. 9. The behavior in time of seven functions of the algorithm M8 for the northern region of Sakhalin Island during the diagnostics period (1979-1993) before the May 27, 1995 Mw 7.1 Neftegorsk earthquake (Tikhonov, 2000). The white circles show the values, calculated for "large" statistics (5 events or more per year), and the black circles show the values for small

statistics (4 events or less per year). Large black circles mark anomalous values.

catalog for the period 1964 – 1978. A dangerous period was found after 1979 (Fig. 9).

We have confirmed the existence of the quiescence zone in (Saprygin et al., 1993). In this paper we advised to reinforce the Northern Sakhalin network of seismic monitoring. However, in this very time because of the economic problems in this country four seismic stations from six, which controlled this region, were closed down. A large number of objects of industrial and civilian purposes were built with the reference seismicity of 6-7 of the *MSK*-64 intensity scale. Thus, there was a deficit of seismic-resistant buildings and structures. That became evident when the May 27, 1995 Neftegorsk earthquake has occurred. The observed ground shaking intensity was 8-9 (MSK-64 scale) in Neftegorsk, and 1841 inhabitants were killed (A memory …, 2000; Streltsov, 2005).

Fig. 8. A seismic quiescence zone (hatched area) in the northern region of Sakhalin Island recognized on the basis of absence the magnitude M 3.0 events since July 1984 (Kim, 1989). The map shows a state of seismicity in April 1988.

We have investigated the intermediate-term precursors of the Neftegorsk earthquake by means of the M8 algorithm (Keilis-Borok & Kossobokov, 1986, 1990; Tikhonov, 2000). It was applied for the retrospective diagnostics of TIP for this earthquake. We used the declustered

We have confirmed the existence of the quiescence zone in (Saprygin et al., 1993). In this paper we advised to reinforce the Northern Sakhalin network of seismic monitoring. However, in this very time because of the economic problems in this country four seismic stations from six, which controlled this region, were closed down. A large number of objects of industrial and civilian purposes were built with the reference seismicity of 6-7 of the *MSK*-64 intensity scale. Thus, there was a deficit of seismic-resistant buildings and structures. That became evident when the May 27, 1995 Neftegorsk earthquake has occurred. The observed ground shaking intensity was 8-9 (MSK-64 scale) in Neftegorsk, and

Fig. 8. A seismic quiescence zone (hatched area) in the northern region of Sakhalin Island recognized on the basis of absence the magnitude M 3.0 events since July 1984 (Kim, 1989).

We have investigated the intermediate-term precursors of the Neftegorsk earthquake by means of the M8 algorithm (Keilis-Borok & Kossobokov, 1986, 1990; Tikhonov, 2000). It was applied for the retrospective diagnostics of TIP for this earthquake. We used the declustered

The map shows a state of seismicity in April 1988.

1841 inhabitants were killed (A memory …, 2000; Streltsov, 2005).

regional catalog (Keilis-Borok et al., 1980). The M8 algorithm was adjusted to the earthquake catalog for the period 1964 – 1978. A dangerous period was found after 1979 (Fig. 9).

In this case data processing was performed under a strong shortage of data (only 4-5 events per year). Dr. Kossobokov analyzed two cases in the similar poor data conditions for the use of the M8 algorithm - deep earthquakes of the Vrancha region (Kossobokov, 1986) and seismicity in Greece (Latoussakis & Kossobokov, 1990). In the first case small and "large" statistics was equal to 2 and 4 events per year but in the second case it was equal to 5 and 10 events per year. However, even under such unfavorable conditions the M8 algorithm has demonstrated an ability to recognize the danger.

In our case only one dangerous period was revealed a posteriori since 1991 when six functions became anomalous (B function was undefined because of poor statistics of small earthquakes). The alarm period was interrupted by the May 27, 1995 Mw 7.1 Neftegorsk earthquake (Fig. 10).

Fig. 9. The behavior in time of seven functions of the algorithm M8 for the northern region of Sakhalin Island during the diagnostics period (1979-1993) before the May 27, 1995 Mw 7.1 Neftegorsk earthquake (Tikhonov, 2000). The white circles show the values, calculated for "large" statistics (5 events or more per year), and the black circles show the values for small statistics (4 events or less per year). Large black circles mark anomalous values.

Current State of Art in Earthquake Prediction, Typical Precursors and

point is evaluated using the standard z test (Habermann, 1981, 1982)

 *z*(*t*) = (*R*all – *Rwl*) / (<sup>2</sup>

moment of seismic quiescence occurrence:

with M 6.8, H 100 km.

defined in the following way:

 *AS*(*t*) = (*R1* – *R2*) / (<sup>2</sup>*1* / *n1* + <sup>2</sup>

**4.3.2 Methodology** 

deviation.

in these periods.

Experience in Earthquake Forecasting at Sakhalin Island and Surrounding Areas 59

The ZMAP method (Wiemer & Wyss, 1994) was developed to reveal a change in rate of seismicity as a function of space and time. The authors have used a rectangular grid with a spacing of 2 km for the total studied area about 100 by 100 km. For each grid point *Ni* nearest epicenters are selected and the maximum distance of an earthquake from the *i*-th grid point *r*(*Ni*) was calculated. Thus the defined *r*(*Ni*) is a function of space proportional to the local density of earthquakes. The significance of change in seismicity rate for each grid

where *R*all и *Rwl* are the mean rates of seismic process in all observation period (from *t*o to *t*e) and in sliding window *wl*, respectively. *n* indicates the number of samples, is the standard

To visualize the changes in the rate of seismicity the authors plotted z(t) values on a map. Moment *t* moves through the whole period of the catalog from *t*o to *t*e. To identify the strongest rate changes between two intervals (from *t*o to *t* and from *t* to *t*e) they have used the *AS*(*t*) function (*Habermann, 1983, 1987, 1991*). This function gives the most probable

where *R1* , *R2* are the mean rates of seismic process in two periods (from *t*o to *t* and from *t* to *t*e), *n1* and *n2* are the numbers of samples in these periods, *1*, *2* are the standard deviations

In the process of application of the ZMAP-technique the following tasks were executed for

 A modification of the ZMAP-method for application to a large territory in a real time scale has been executed. After the modification the task was implemented using the standard deviate *z* test (Habermann, 1981, 1982) in two steps: (1) Detection of seismic quiescence in a studied region using a coarse rectangular grid with a moderate number of nodes (with a spacing of 0.250); (2) Covering the cells where seismic quiescence was detected by a detailed grid (with a spacing of 0.10) and calculation of a configuration of

 An adjusting of the modified ZMAP*-*technique to the JMA earthquake catalog for the detection of possible seismic quiescence periods before the strong shallow earthquakes

An investigation of the precursor seismic quiescence since July 2001 within the studied area.

In order to effectuate the first step of methodology we divided the studied territory into grids spacing 0.250 in latitude and longitude (Fig. 11). An adjustment of a modified method was performed to the declustered earthquake catalog for the period 1975 – 1988. The values of *z*(*t*) function were identified as anomalous if they exceeded a proper threshold calculated for the adjusting time span. Thresholds *Ui* for detection of quiescence in separate nodes was

> *i + coef*

*Ui* (*coef*) *=* 

detection of seismic quiescence periods in the Japan region (Tikhonov, 2003, 2005):

anomalous area with a given value of seismicity rate decrease.

**4.3.3 Results of analysis and precursors phenomena** 

all / *n*all + <sup>2</sup>

*wl* / *nwl*)1/2, (4)

*<sup>2</sup>* / *n2*)1/2, (5)

*i* , (6)

Fig. 10. Epicenters of the May 27, 1995 Mw 7.1 Neftegorsk earthquake and first-day aftershocks of magnitude M ≥ 3.5.

#### **4.3 Case 3 - Incomplete forecasting of the Tokachi-oki Mw 8.3 earthquake (Hokkaido Island, Japan)**

The M8 algorithm has failed in prognosis of the Tokachi-oki Mw 8.3 earthquake (http://mitp.ru/predictions/html, this site is of access for experts only since 2000 year). Despite of the failure of the M8 algorithm, the described below ZMAP-technique performed by one of the authors was successful (Tikhonov, 2003; 2005).

#### **4.3.1 Seismic region and data**

In this case the territory of the Japanese Islands including the adjacent shelf areas (Fig. 11) was examined. The Japan Meteorological Agency earthquake catalog from January 1974 until July 2002 was used. Earthquakes with M 3.8, H 100 km were found to be completely recorded, and these events were taken into account (Fig. 11). This data set is quite homogeneous throughout the whole region of Japan. It permits to apply the ZMAPtechnique (Wiemer & Wyss, 1994) for examination. This method could not be applied in the cases 1 and 2 because of a shortage of data and difference in data availability for the Northern and Southern areas of the Sakhalin Island.

#### **4.3.2 Methodology**

58 Earthquake Research and Analysis – Statistical Studies, Observations and Planning

Fig. 10. Epicenters of the May 27, 1995 Mw 7.1 Neftegorsk earthquake and first-day

by one of the authors was successful (Tikhonov, 2003; 2005).

Northern and Southern areas of the Sakhalin Island.

**4.3 Case 3 - Incomplete forecasting of the Tokachi-oki Mw 8.3 earthquake (Hokkaido** 

The M8 algorithm has failed in prognosis of the Tokachi-oki Mw 8.3 earthquake (http://mitp.ru/predictions/html, this site is of access for experts only since 2000 year). Despite of the failure of the M8 algorithm, the described below ZMAP-technique performed

In this case the territory of the Japanese Islands including the adjacent shelf areas (Fig. 11) was examined. The Japan Meteorological Agency earthquake catalog from January 1974 until July 2002 was used. Earthquakes with M 3.8, H 100 km were found to be completely recorded, and these events were taken into account (Fig. 11). This data set is quite homogeneous throughout the whole region of Japan. It permits to apply the ZMAPtechnique (Wiemer & Wyss, 1994) for examination. This method could not be applied in the cases 1 and 2 because of a shortage of data and difference in data availability for the

aftershocks of magnitude M ≥ 3.5.

**4.3.1 Seismic region and data** 

**Island, Japan)** 

The ZMAP method (Wiemer & Wyss, 1994) was developed to reveal a change in rate of seismicity as a function of space and time. The authors have used a rectangular grid with a spacing of 2 km for the total studied area about 100 by 100 km. For each grid point *Ni* nearest epicenters are selected and the maximum distance of an earthquake from the *i*-th grid point *r*(*Ni*) was calculated. Thus the defined *r*(*Ni*) is a function of space proportional to the local density of earthquakes. The significance of change in seismicity rate for each grid point is evaluated using the standard z test (Habermann, 1981, 1982)

$$z(t) \equiv \left(R\_{\text{all}} - R\_{\text{wl}}\right) / \left(\sigma^2 \, \_{\text{all}} / \, n\_{\text{all}} + \sigma^2 \, \_{\text{wl}} / \, n\_{\text{wl}}\right) 1/2 \tag{4}$$

where *R*all и *Rwl* are the mean rates of seismic process in all observation period (from *t*o to *t*e) and in sliding window *wl*, respectively. *n* indicates the number of samples, is the standard deviation.

To visualize the changes in the rate of seismicity the authors plotted z(t) values on a map. Moment *t* moves through the whole period of the catalog from *t*o to *t*e. To identify the strongest rate changes between two intervals (from *t*o to *t* and from *t* to *t*e) they have used the *AS*(*t*) function (*Habermann, 1983, 1987, 1991*). This function gives the most probable moment of seismic quiescence occurrence:

$$AS(t) = (R\_1 - R\_2) \;/\; (\sigma\_1^2 \;/\; n\_1 + \sigma\_2^2 \;/\; n\_2)^{1/2},\tag{5}$$

where *R1* , *R2* are the mean rates of seismic process in two periods (from *t*o to *t* and from *t* to *t*e), *n1* and *n2* are the numbers of samples in these periods, *1*, *2* are the standard deviations in these periods.

In the process of application of the ZMAP-technique the following tasks were executed for detection of seismic quiescence periods in the Japan region (Tikhonov, 2003, 2005):


#### **4.3.3 Results of analysis and precursors phenomena**

In order to effectuate the first step of methodology we divided the studied territory into grids spacing 0.250 in latitude and longitude (Fig. 11). An adjustment of a modified method was performed to the declustered earthquake catalog for the period 1975 – 1988. The values of *z*(*t*) function were identified as anomalous if they exceeded a proper threshold calculated for the adjusting time span. Thresholds *Ui* for detection of quiescence in separate nodes was defined in the following way:

$$\text{all}\_{i}\,\text{(coeff)} = \mu\_{i} + \alpha \text{of}\,\,\,\sigma\_{i} \,\,\,\tag{6}$$

Current State of Art in Earthquake Prediction, Typical Precursors and

in January 1998.

January 1998.

**4.3.4 The realization of forecasting** 

Experience in Earthquake Forecasting at Sakhalin Island and Surrounding Areas 61

Fig. 12. The location of the seismic quiescence in the northern part of Japan as on June 1, 2002. Gray circles denote the anomalous nodes. The anomaly of seismic quiescence started

Fig. 13. Map of the seismicity rate decrease calculated for the grid with spacing of 0.10 at the middle of 2002. The seismic quiescence anomaly within the Cape Erimo started in

The Tokach-oki earthquake forecasting was presented during the XXIII General Assembly of IUGG, which was held in Sapporo (June 30 – July 11, 2003) (Tikhonov, 2003). Besides, these

where *i* , *<sup>i</sup>* are the average and the root mean square values of function *z*(*t*) in node *i* for the learning time, respectively; *coef* is empirical constant. The value of *z*(*t*) were identified as anomalous if *z*(*t*) *Ui (coef).* The constant *coef* was taken equal to 4. Thresholds for nodes were selected to minimize a probability of omission of a real seismic quiescence prior the strong earthquakes with M 6.8.

Detection of the areas with anomalous values of *z*(*t*) function has been fulfilled for the declustered catalog data since 1989. Thus, there were facilities for detection of seismic quiescence periods occurring prior a series of large seismic events, which occurred in 1992 – 2002. As a result, we obtained a set of maps of the Japan region showing the location of such areas at different moments of time. Dynamics of the appearance and evolution of the anomalous areas was compared visually with dynamics of the occurrence of the strong earthquakes (M 6.8, H 100 km). It was established that correlation between the most outstanding anomalies and the strong earthquakes was suitable in space and time. In general the maximum size of anomaly is observed about 0.5 – 1.5 yr before the corresponding strong shock. The results of processing of the catalog since 1989 were the following: in 7 cases the occurrence of the strong seismic events was forestalled by seismic quiescence near its epicenters. In general the epicenter is located near the border of the corresponding anomalous zone. In two cases there was no quiescence before the strong earthquakes, and in two cases anomalous areas were observed before swarms of moderate size earthquakes (M = 6.2 – 6.6).

Obviously, the recent seismic quiescence zone revealed in the northern part of Japan had attracted an interest (Fig. 12). The term "recent" dates here back to the time of investigation (the middle of 2002). As a result of the second step of the procedure (with a detailed spacing of 0.10 grid size) the most outstanding recent anomaly of 75 km size was located near the Cape Erimo (Hokkaido Isl.) (Fig. 13). It was characterized by a seismicity rate decrease of 75% starting from January 1998. Inside this anomalous area there was a circle with R=25 km with no earthquake occurrence with M 3.8, H 100.

Fig. 11. Map displaying the grid with spacing of 0.250 used for detection of seismic quiescence. This grid contains 1354 nodes.

the learning time, respectively; *coef* is empirical constant. The value of *z*(*t*) were identified as anomalous if *z*(*t*) *Ui (coef).* The constant *coef* was taken equal to 4. Thresholds for nodes were selected to minimize a probability of omission of a real seismic quiescence prior the

Detection of the areas with anomalous values of *z*(*t*) function has been fulfilled for the declustered catalog data since 1989. Thus, there were facilities for detection of seismic quiescence periods occurring prior a series of large seismic events, which occurred in 1992 – 2002. As a result, we obtained a set of maps of the Japan region showing the location of such areas at different moments of time. Dynamics of the appearance and evolution of the anomalous areas was compared visually with dynamics of the occurrence of the strong earthquakes (M 6.8, H 100 km). It was established that correlation between the most outstanding anomalies and the strong earthquakes was suitable in space and time. In general the maximum size of anomaly is observed about 0.5 – 1.5 yr before the corresponding strong shock. The results of processing of the catalog since 1989 were the following: in 7 cases the occurrence of the strong seismic events was forestalled by seismic quiescence near its epicenters. In general the epicenter is located near the border of the corresponding anomalous zone. In two cases there was no quiescence before the strong earthquakes, and in two cases anomalous areas were observed before swarms of moderate

Obviously, the recent seismic quiescence zone revealed in the northern part of Japan had attracted an interest (Fig. 12). The term "recent" dates here back to the time of investigation (the middle of 2002). As a result of the second step of the procedure (with a detailed spacing of 0.10 grid size) the most outstanding recent anomaly of 75 km size was located near the Cape Erimo (Hokkaido Isl.) (Fig. 13). It was characterized by a seismicity rate decrease of 75% starting from January 1998. Inside this anomalous area there was a circle with R=25 km

Fig. 11. Map displaying the grid with spacing of 0.250 used for detection of seismic

*<sup>i</sup>* are the average and the root mean square values of function *z*(*t*) in node *i* for

where *i* , 

strong earthquakes with M 6.8.

size earthquakes (M = 6.2 – 6.6).

with no earthquake occurrence with M 3.8, H 100.

quiescence. This grid contains 1354 nodes.

Fig. 12. The location of the seismic quiescence in the northern part of Japan as on June 1, 2002. Gray circles denote the anomalous nodes. The anomaly of seismic quiescence started in January 1998.

Fig. 13. Map of the seismicity rate decrease calculated for the grid with spacing of 0.10 at the middle of 2002. The seismic quiescence anomaly within the Cape Erimo started in January 1998.

#### **4.3.4 The realization of forecasting**

The Tokach-oki earthquake forecasting was presented during the XXIII General Assembly of IUGG, which was held in Sapporo (June 30 – July 11, 2003) (Tikhonov, 2003). Besides, these

Current State of Art in Earthquake Prediction, Typical Precursors and

Sakhalin Island.

**4.4.2 Methodology** 

of the Kuril Islands.

ongoing strong earthquake.

fault zones of lower seismic potential.

nonlinear differential equation of the second order:

**4.4.3 Precursors phenomena and characteristics of prediction** 

Experience in Earthquake Forecasting at Sakhalin Island and Surrounding Areas 63

arrangement of three major fault systems marked by recent seismic activity. These are the

We used two data sets in this study: (1) the catalog of shallow earthquakes for 1992–2002 from the IRIS-2 system, installed at the "Yuzhno-Sakhalinsk" seismic station in 1992 (Kraeva, 2003); (2) the catalog of network of digital "Datamark" and "DAT" autonomous seismic stations, operating since 2001. The first catalog provides a record of all M > 2.6 seismic events within epicenter distances up to 70 km from the station. The second catalog is more detailed and provides analysis of seismicity patterns in the whole southern part of

This prediction was based on the detection of seismic gaps of the first and second kind. Let us describe these terms for the examined situation of the moderate seismic activity of the Sakhalin Island in detail. A gap of the first kind refers to a portion of a seismic area that has been in a state of relative rest for a long time (100 years and more), i.e., there have been no earthquakes with magnitude M ≥ 6.0 during this period. A gap of the second kind (seismic quiescence) refers to a portion of a seismic area of low seismic activity with no earthquakes with М ≥ 3.0 observed for a period of several years. Note that in the case 1 the second kind gap was examined for the magnitude threshold M = 6.0 because of the higher seismic level

We have used also the method of self-developing processes suggested by Malyshev (Malyshev, 1991; Malyshev et al., 1992). It was found that behavior of empirical earthquake sequences before and after large seismic events is satisfactory described by solutions of a

2

, (7)

<sup>2</sup> <sup>2</sup>

2 0 *d x dx k V dt dt*

where *x* is a parameter of process (for example, a cumulative sum of a number of shocks – *N* parameter), 0 <sup>0</sup> *V dx dt* / is a rate of seismic process in stationary state, *k* and are empirical constants. Particular solution of the equation in case of 2 > 1 has a vertical asymptote. The time position of this asymptote is shown to be close to the origin time of the

Apparently, each of three above mentioned fault zones has the potential to originate major earthquakes Ms 7.0–7.5. However, evidence is currently limited to the Rebun–Moneron (the 1971 Moneron earthquake, Ms 7.5) and the Central Sakhalin (paleoseismological data) fault zones. The Western Sakhalin fault zone showed no magnitude М > 5.0 events in its southern part during the whole history of instrumental observations up to 2006 (Fig. 15). However in its northern part (latitude>48°N) it has originated large earthquakes in 1907 (Alexandrovsk– Sakhalinsk, Ms 6.5), 1924 (Lesogorsk–Uglegorsk, Ms 6.9), and 2000 (Uglegorsk, Ms 7.2) (Fig. 16). Besides these three major fault zones in the studied area there are a number of small

Rebun–Moneron, the Western, and the Central Sakhalin fault zones (Fig. 15).

results were published in (Tikhonov, 2005). The manuscript of the paper was received by the Journal of Volcanology and Seismology on 6 August 2003, i.e. before the occurrence of the Tokachi-oki earthquake. The Tokachi-oki earthquake Mw 8.3 occurred on September 26, at 4 h 50 min JST time near the southern coast of Hokkaido close to the seismic quiescence zone (Fig. 14).

Fig. 14. Map of the 26 September, Mw 8.3 Tokachi-oki earthquake epicenter (large circle) and its first-day aftershocks of magnitude M≥5.0 (small circles).

#### **4.3.5 Case 3 summary**

The modified ZMAP-method has been applied to detect precursory seismic quiescence zones in the Japan region. The anomalies revealed for the period 1989 – 2000 correlate in space and time with the strong event occurrences. The greatest size of anomalous area took place typically about 0.5 – 1.5 yr before the corresponding strong shock.

The anomalous decrease of shallow seismicity (M 3.8) was detected in the southern part of Hokkaido islands at the middle of 2002. In result of the second stage of the procedure the anomaly of 75 km size was determined. It was characterized by a seismicity rate decrease of 75% from January 1998. Moreover, inside this zone there was a circle of 25 km radius with 100% decrease of the rate. The Tokachi-oki earthquake Mw 8.3 has occurred on September 26, at 4 h 50 min JST time close to the seismic quiescence zone (Fig. 14).

#### **4.4 Case 4 - A successful prediction of the 2 August, 2007 Nevelsk earthquake (Mw 6.2) in Southern Sakhalin Island**

#### **4.4.1 Seismic region and data**

The object of this investigation was the southern part of the Sakhalin Island (south of latitude 48°N). The basic feature of the Earth's crust in this region is characterized by close arrangement of three major fault systems marked by recent seismic activity. These are the Rebun–Moneron, the Western, and the Central Sakhalin fault zones (Fig. 15).

We used two data sets in this study: (1) the catalog of shallow earthquakes for 1992–2002 from the IRIS-2 system, installed at the "Yuzhno-Sakhalinsk" seismic station in 1992 (Kraeva, 2003); (2) the catalog of network of digital "Datamark" and "DAT" autonomous seismic stations, operating since 2001. The first catalog provides a record of all M > 2.6 seismic events within epicenter distances up to 70 km from the station. The second catalog is more detailed and provides analysis of seismicity patterns in the whole southern part of Sakhalin Island.

### **4.4.2 Methodology**

62 Earthquake Research and Analysis – Statistical Studies, Observations and Planning

results were published in (Tikhonov, 2005). The manuscript of the paper was received by the Journal of Volcanology and Seismology on 6 August 2003, i.e. before the occurrence of the Tokachi-oki earthquake. The Tokachi-oki earthquake Mw 8.3 occurred on September 26, at 4 h 50 min JST time near the southern coast of Hokkaido close to the seismic quiescence

Fig. 14. Map of the 26 September, Mw 8.3 Tokachi-oki earthquake epicenter (large circle)

The modified ZMAP-method has been applied to detect precursory seismic quiescence zones in the Japan region. The anomalies revealed for the period 1989 – 2000 correlate in space and time with the strong event occurrences. The greatest size of anomalous area took

The anomalous decrease of shallow seismicity (M 3.8) was detected in the southern part of Hokkaido islands at the middle of 2002. In result of the second stage of the procedure the anomaly of 75 km size was determined. It was characterized by a seismicity rate decrease of 75% from January 1998. Moreover, inside this zone there was a circle of 25 km radius with 100% decrease of the rate. The Tokachi-oki earthquake Mw 8.3 has occurred on September

**4.4 Case 4 - A successful prediction of the 2 August, 2007 Nevelsk earthquake (Mw** 

The object of this investigation was the southern part of the Sakhalin Island (south of latitude 48°N). The basic feature of the Earth's crust in this region is characterized by close

and its first-day aftershocks of magnitude M≥5.0 (small circles).

place typically about 0.5 – 1.5 yr before the corresponding strong shock.

26, at 4 h 50 min JST time close to the seismic quiescence zone (Fig. 14).

zone (Fig. 14).

**4.3.5 Case 3 summary** 

**6.2) in Southern Sakhalin Island 4.4.1 Seismic region and data** 

This prediction was based on the detection of seismic gaps of the first and second kind. Let us describe these terms for the examined situation of the moderate seismic activity of the Sakhalin Island in detail. A gap of the first kind refers to a portion of a seismic area that has been in a state of relative rest for a long time (100 years and more), i.e., there have been no earthquakes with magnitude M ≥ 6.0 during this period. A gap of the second kind (seismic quiescence) refers to a portion of a seismic area of low seismic activity with no earthquakes with М ≥ 3.0 observed for a period of several years. Note that in the case 1 the second kind gap was examined for the magnitude threshold M = 6.0 because of the higher seismic level of the Kuril Islands.

We have used also the method of self-developing processes suggested by Malyshev (Malyshev, 1991; Malyshev et al., 1992). It was found that behavior of empirical earthquake sequences before and after large seismic events is satisfactory described by solutions of a nonlinear differential equation of the second order:

$$\frac{d^2\mathbf{x}}{dt^2} = k \left| \left(\frac{d\mathbf{x}}{dt}\right)^2 - V\_0^2 \right|^{\mathcal{V}},\tag{7}$$

where *x* is a parameter of process (for example, a cumulative sum of a number of shocks – *N* parameter), 0 <sup>0</sup> *V dx dt* / is a rate of seismic process in stationary state, *k* and are empirical constants. Particular solution of the equation in case of 2 > 1 has a vertical asymptote. The time position of this asymptote is shown to be close to the origin time of the ongoing strong earthquake.

#### **4.4.3 Precursors phenomena and characteristics of prediction**

Apparently, each of three above mentioned fault zones has the potential to originate major earthquakes Ms 7.0–7.5. However, evidence is currently limited to the Rebun–Moneron (the 1971 Moneron earthquake, Ms 7.5) and the Central Sakhalin (paleoseismological data) fault zones. The Western Sakhalin fault zone showed no magnitude М > 5.0 events in its southern part during the whole history of instrumental observations up to 2006 (Fig. 15). However in its northern part (latitude>48°N) it has originated large earthquakes in 1907 (Alexandrovsk– Sakhalinsk, Ms 6.5), 1924 (Lesogorsk–Uglegorsk, Ms 6.9), and 2000 (Uglegorsk, Ms 7.2) (Fig. 16). Besides these three major fault zones in the studied area there are a number of small fault zones of lower seismic potential.

Current State of Art in Earthquake Prediction, Typical Precursors and

Experience in Earthquake Forecasting at Sakhalin Island and Surrounding Areas 65

Fig. 17. Map of crust earthquake М≥3.0 epicenters, 1993–2005, recorded by the "Datamark"

network of stations and the "IRIS-2" system, installed at the "Yuzhno–Sakhalinsk"

Note: the area of the seismic gap of the second kind is outlined with the bold dash line, while the source zones of the 17 August 2006, Мw 5.6 Gornozavodsk and the 2 August 2007, Мw 6.2 Nevelsk earthquakes, with a thin dash line; asterisks indicate the epicenters of main shocks; focal mechanisms are given based on data from [http://www.globalcmt.org]. The area limited by the polygon is the geographical area within which a large earthquake

seismic station.

M=6.6±0.6 may occur.

Fig. 15. Map of crust earthquake М > 5.0 epicenters of southern Sakhalin, 1906–2005, and the main fault zones.

Notes: The active faults are plotted according to M.I. Streltsov of IMG&G FEB RAS, Yuzhno-Sakhalinsk (1) and A.I. Kozhurin, of GIN AS, Moscow (2).

Fig. 16. Sources of large earthquakes at the western coast of Sakhalin Island (grey ovals) and the approximate location of the seismic gap of the first kind (hatched rectangle).

Fig. 15. Map of crust earthquake М > 5.0 epicenters of southern Sakhalin, 1906–2005, and the

Notes: The active faults are plotted according to M.I. Streltsov of IMG&G FEB RAS, Yuzhno-

Fig. 16. Sources of large earthquakes at the western coast of Sakhalin Island (grey ovals) and

the approximate location of the seismic gap of the first kind (hatched rectangle).

Sakhalinsk (1) and A.I. Kozhurin, of GIN AS, Moscow (2).

main fault zones.

Fig. 17. Map of crust earthquake М≥3.0 epicenters, 1993–2005, recorded by the "Datamark" network of stations and the "IRIS-2" system, installed at the "Yuzhno–Sakhalinsk" seismic station.

Note: the area of the seismic gap of the second kind is outlined with the bold dash line, while the source zones of the 17 August 2006, Мw 5.6 Gornozavodsk and the 2 August 2007, Мw 6.2 Nevelsk earthquakes, with a thin dash line; asterisks indicate the epicenters of main shocks; focal mechanisms are given based on data from [http://www.globalcmt.org]. The area limited by the polygon is the geographical area within which a large earthquake M=6.6±0.6 may occur.

Current State of Art in Earthquake Prediction, Typical Precursors and

142.0° E); (46.9° N; 142.2° E); (47.6° N; 142.3° E).

to determine the expected magnitude M=6.1.

obtain:

This gives M=6.6.

large earthquake.

The beginning and end of alarm

January, 2006– July, 2013

Experience in Earthquake Forecasting at Sakhalin Island and Surrounding Areas 67

of the second kind in the area of 90 by 60 km where seismic quiescence was confirmed by accurate data from "Datamark" digital network (Fig. 17); and 3) the accelerated sequence of

 The location of the incipient hypocenter is most likely to occur at shallow depths within 0–30 km inside the polygon (Fig. 17): (47.6° N; 141.2° E); (46.5° N; 140.8° E); (46.4° N;

 The magnitude Ms of the incipient event was estimated in two different ways. The first is the formula by K. Tanaka (1980) lg R=0.33 M−0.07, which relates the linear size of the gap of the second kind, R, to the magnitude of expected earthquake, M. It was used first

 The second estimate was obtained from the two empirical relations: (1) lg L=(0.5±0.01) M−(1.77±0.07) (Tarakanov, 1995); and (2) L ≈ 1/3 R, where L is the linear size of the aftershock zone (Shebalin, 1961). Substituting an expression (2) in the formula (1), we

 Of the two estimates, the second appears to be preferable because it takes into account the worst earthquake scenario as well as some uncertainty in estimates. Therefore, Ms=6.6±0.6 was selected as a final magnitude estimate of the expected

 The duration of alarm was determined to be about 7.5 years. This was based on an average time-span of approximately 10 years, observed for seismic quiescence zones that occurred before large earthquakes off the western coast of Japan and Sakhalin, while accounting for no less than 2.5 years of a given quiescence zone's initiation. The likelihood of an earthquake occurrence was estimated at 75%, based on the recurrence rate of the large (М ≥ 6.5) earthquakes in the south of Sakhalin (Oskorbin &

 The expected intensity of ground shaking (in the MSK-64 scale) was calculated for the three epicenter locations inside the seismic gap of the second kind and the magnitude close to the maximal expected. Fig. 19 displays the results obtained with the epicenter in

> Position of earthquake epicenter

> See the text

The prediction described was submitted in January 2006 to the Russian Expert Council for Earthquake Prediction, Seismic Hazard and Risk of the Russian Academy of Sciences and the Ministry of Emergency Situations (REC RAS/EmerCom). As a result of the discussion at the REC Meeting, the prediction was approved as being scientifically motivated. It was then reported to EmerCom headquarters, which had run urgent command-staff exercises in August 2006, referred to as "Mitigating the consequences of destructive earthquake and

Table 1. Characteristics of anticipated earthquake (Tikhonov, 2006, page 179).

Bobkov, 1997) and the lifespan of a given quiescence zone.

the middle of the quiescence zone.

Magnitude and depth of earthquake

МS = 6.0 – 7.2 h = 0 – 30 km

lg R=(0.5±0.01) M−(1.77±0.07)+lg 3. (8)

Probability of earthquake occurrence

and Fig. 17 75% 9.0 (in epicenter)

Maximal macroseismic effect (MSK-64 scale)

8.0 (at the coast)

earthquakes in the area adjacent to it (Fig. 18). The prediction was the following:

An earlier publication (Tikhonov, 1997) recognized an incipient of the second kind gap (seismic quiescence) within one of the gaps of the first kind, situated on the western coast of southern Sakhalin. In December 2005 our analysis of the southern Sakhalin network data permitted to made it possible to: (1) outline rather precisely the area of a seismic gap of the second kind, where shallow earthquakes with magnitudeМ ≥ 3.0 did not occur from at least the middle of 2003 (Fig. 17); and (2) observe the appreciable revival of seismic activity that eventually encircled this area by 2003 (Fig. 18).

Furthermore, the rise of activity around the seismic quiescence zone, and the area south of it, has accelerated (Fig. 18) with culminations linked to the 30 May 2004 Kostroma, Ms=4.8 earthquake in the Western Sakhalin fault zone and the 18 December 2004 Moneron, Ms=4.7 earthquake in the epicenter area of the major 1971 Moneron earthquake. This happened while the seismic sequence of the abovementioned 2001 Takoye earthquake swarm in the Central Sakhalin fault zone was still ongoing.

Fig. 18. The cumulative number of shallow earthquakes (depth above 30 km) of magnitude 3 or more inside 45.5–46.75°N and 140.8–142.2°E (i.e., next to the southern area of the identified seismic gap of the second kind) as a function of time in September 1996–May 2006. Note: the smooth line models the inverse power law acceleration of the empirical data according to the method suggested by Malyshev et al. (1992). The line has the asymptote at 26 August 2007.

At the time, Dr. Tikhonov, in collaboration with Ch.U. Kim, A.I. Ivashchenko and L.N. Poplavskaya (Institute of Marine Geology and Geophysics, Yuzhno–Sakhalinsk) issued the long-term prediction of major earthquake near the western coast of southern Sakhalin (Tikhonov, 2006). This strong earthquake prediction summarized in Table 1 was made by taking into account 1) the seismic gap of the first kind in the Western Sakhalin system of faults, where large earthquakes were absent for at least 100 years (Fig. 16); 2) the seismic gap of the second kind in the area of 90 by 60 km where seismic quiescence was confirmed by accurate data from "Datamark" digital network (Fig. 17); and 3) the accelerated sequence of earthquakes in the area adjacent to it (Fig. 18). The prediction was the following:


$$\text{lg R} = (0.5 \pm 0.01) \text{ M} - (1.77 \pm 0.07) + \text{lg } 3. \tag{8}$$

This gives M=6.6.

66 Earthquake Research and Analysis – Statistical Studies, Observations and Planning

An earlier publication (Tikhonov, 1997) recognized an incipient of the second kind gap (seismic quiescence) within one of the gaps of the first kind, situated on the western coast of southern Sakhalin. In December 2005 our analysis of the southern Sakhalin network data permitted to made it possible to: (1) outline rather precisely the area of a seismic gap of the second kind, where shallow earthquakes with magnitudeМ ≥ 3.0 did not occur from at least the middle of 2003 (Fig. 17); and (2) observe the appreciable revival of seismic activity that

Furthermore, the rise of activity around the seismic quiescence zone, and the area south of it, has accelerated (Fig. 18) with culminations linked to the 30 May 2004 Kostroma, Ms=4.8 earthquake in the Western Sakhalin fault zone and the 18 December 2004 Moneron, Ms=4.7 earthquake in the epicenter area of the major 1971 Moneron earthquake. This happened while the seismic sequence of the abovementioned 2001 Takoye earthquake swarm in the

Fig. 18. The cumulative number of shallow earthquakes (depth above 30 km) of magnitude 3 or more inside 45.5–46.75°N and 140.8–142.2°E (i.e., next to the southern area of the identified

At the time, Dr. Tikhonov, in collaboration with Ch.U. Kim, A.I. Ivashchenko and L.N. Poplavskaya (Institute of Marine Geology and Geophysics, Yuzhno–Sakhalinsk) issued the long-term prediction of major earthquake near the western coast of southern Sakhalin (Tikhonov, 2006). This strong earthquake prediction summarized in Table 1 was made by taking into account 1) the seismic gap of the first kind in the Western Sakhalin system of faults, where large earthquakes were absent for at least 100 years (Fig. 16); 2) the seismic gap

seismic gap of the second kind) as a function of time in September 1996–May 2006. Note: the smooth line models the inverse power law acceleration of the empirical data according to the method suggested by Malyshev et al. (1992). The line has the asymptote at

eventually encircled this area by 2003 (Fig. 18).

Central Sakhalin fault zone was still ongoing.

26 August 2007.



Table 1. Characteristics of anticipated earthquake (Tikhonov, 2006, page 179).

The prediction described was submitted in January 2006 to the Russian Expert Council for Earthquake Prediction, Seismic Hazard and Risk of the Russian Academy of Sciences and the Ministry of Emergency Situations (REC RAS/EmerCom). As a result of the discussion at the REC Meeting, the prediction was approved as being scientifically motivated. It was then reported to EmerCom headquarters, which had run urgent command-staff exercises in August 2006, referred to as "Mitigating the consequences of destructive earthquake and

Current State of Art in Earthquake Prediction, Typical Precursors and

listed in the Table 1.

GIN AS, Moscow (2).

(Levin et al., 2007; Tikhonov & Kim, 2010).

Experience in Earthquake Forecasting at Sakhalin Island and Surrounding Areas 69

Inspections into the consequences of this disaster have shown that the city needs to be rebuilt practically anew. The losses totaled more than six billion rubles (i.e., \$240 million). The focal mechanism of the main shock, based on data from (http://www.globalcmt.org), suggests that the source region was under the sub-latitudinal and near-horizontal compression that resulted in the reverse-slip (Fig. 17). IMG&G and employees of the Sakhalin Branch of Geophysical Survey of the RAS carried out a general inspection of the region affected by the earthquake. Other organizations provided the aerial mapping and echo sounding of the sea-bottom. The seismic event appeared to be related to the West-Sakhalin system of deep crustal faults located along the western coast of the island. As a result of the general inspection, a number of unique observations for earthquakes of such size have been established. One of the most remarkable geodynamic phenomena associated with the 2007 Nevelsk earthquake is the uplift of the coastal terrace, formed by the Middle

Miocene sedimentary rocks (Nevelsk suite), with an amplitude of 1.0–1.5 m (Fig. 21).

Fig. 20. Map of the 17 August 2006, Мw 5.6 Gornozavodsk and 2 August 2007, Мw 6.2

Nevelsk earthquake epicenters (asterisks) and their first-day aftershocks of magnitude М ≥ 2.8. Notes: the clusters of epicenters are outlined with a dash line. The active faults are plotted according to M.I. Streltsov of IMG&G FEB RAS, Yuzhno-Sakhalinsk (1) and A.I. Kozhurin, of

The 2 August 2007, Mw 6.2 Nevelsk earthquake occurred in the southern part of the seismic gap of the second kind (Fig. 17). Its parameters fall within the limits of the long-term prediction of a large earthquake expected in the southwest of Sakhalin Island, as it was

Thus, the long-term prediction of December 2005 was confirmed. Note also that the decision that the 17 August 2006 Gornozavodsk earthquake was a foreshock of a future large event was declared just after this event (23 August 2006). More details concerning case histories of prediction of the 2006 Gornozavodsk and the 2007 Nevelsk earthquakes can be found in

tsunami in Sakhalin–Kuril region." The scientific motivations of the prediction have been published (Tikhonov, 2006).

Fig. 19. An expected ground shaking intensity (MSK-64 scale) for the model occurrence of an earthquake of Ms 7.0 at a depth of 20 km in the central part of the seismic quiescence zone (computations by L.N. Poplavskaya of IMG&G FEB RAS made in December 2005).
