**4.4.4 The realization of the prediction**

On 17 August 2006, a magnitude Mw 5.6 earthquake hit the Gornozavodsk settlement in the area of prediction (Levin et al., 2007). Upon analyzing the main shock and its aftershocks, a conclusion of the precursory character of this sequence was drawn. Specifically, it was concluded that the preparation of a large earthquake in the seismic quiescence zone had switched from a long-term to a short-term phase.

This was briefly formulated in the cover letter of an interim report to REC RAS/EmerCom, as follows: "In December 2005, the seismology team of IMG&G FEB RAS issued a long-term prediction of strong earthquake on southwest shelf of Sakhalin Island. Recent M 5.6 earthquake, which happened in this region on 17 (18) August 2006, has partially proved the prediction to be well-founded. Detailed analysis of post-earthquake seismicity allows to conclude that the development of predicted earthquake is in the short-term stage now…".

On August 2, at 13 h 37 min Sakhalin time (2 h 37 min GMT), in the Tatar Strait close to the city of Nevelsk (Sakhalin, Russia), an earthquake of magnitude Mw 6.2 occurred (Fig. 20). Two lives were lost and more than ten persons were wounded. The earthquake caused severe destruction. About six thousand of Nevelsk's fifteen thousand inhabitants became homeless. The earthquake was felt everywhere in the southern portion of Sakhalin Island. The observed groundshaking intensity (MSK-64 scale) was VII–VIII in Nevelsk, VI–VII in Gornozavodsk, V–VI in Holmsk and III–IV in Yuzhno-Sakhalinsk.

tsunami in Sakhalin–Kuril region." The scientific motivations of the prediction have been

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).

On 17 August 2006, a magnitude Mw 5.6 earthquake hit the Gornozavodsk settlement in the area of prediction (Levin et al., 2007). Upon analyzing the main shock and its aftershocks, a conclusion of the precursory character of this sequence was drawn. Specifically, it was concluded that the preparation of a large earthquake in the seismic quiescence zone had

This was briefly formulated in the cover letter of an interim report to REC RAS/EmerCom, as follows: "In December 2005, the seismology team of IMG&G FEB RAS issued a long-term prediction of strong earthquake on southwest shelf of Sakhalin Island. Recent M 5.6 earthquake, which happened in this region on 17 (18) August 2006, has partially proved the prediction to be well-founded. Detailed analysis of post-earthquake seismicity allows to conclude that the development of predicted earthquake is in the short-term stage now…". On August 2, at 13 h 37 min Sakhalin time (2 h 37 min GMT), in the Tatar Strait close to the city of Nevelsk (Sakhalin, Russia), an earthquake of magnitude Mw 6.2 occurred (Fig. 20). Two lives were lost and more than ten persons were wounded. The earthquake caused severe destruction. About six thousand of Nevelsk's fifteen thousand inhabitants became homeless. The earthquake was felt everywhere in the southern portion of Sakhalin Island. The observed groundshaking intensity (MSK-64 scale) was VII–VIII in Nevelsk, VI–VII in

published (Tikhonov, 2006).

**4.4.4 The realization of the prediction** 

switched from a long-term to a short-term phase.

Gornozavodsk, V–VI in Holmsk and III–IV in Yuzhno-Sakhalinsk.

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).

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 listed in the Table 1.

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

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 GIN AS, Moscow (2).

Current State of Art in Earthquake Prediction, Typical Precursors and

as presumably registered without admissions.

Experience in Earthquake Forecasting at Sakhalin Island and Surrounding Areas 71

data from December 1995 until December 2007; events with M 4.0 were taken into account

Fig. 22. Map of earthquake M ≥ 5.9 epicenters near Kuril Islands, May 1999 – January 2010.

It was shown by the examples above that the M8 algorithm and the detection of seismic gaps of the first and the second type provide a reasonable first approach to a long- and intermediate-term earthquake prognosis. The decrease in *b*-values is known also as a precursor of strong earthquake occurrence. In (Tikhonov, 1999, 2000) it was attempted to present and apply a new formal algorithm for detection of both areas of intermediate- and short-term seismic quiescence and change in b-value using a few functions that characterize these features of seismic regime. This algorithm was named Q1. It was elaborated in analogy with the structure of the M8 algorithm. The detailed description of the Q1 algorithm is presented in (Tikhonov, 2000). We do not describe the Q1 algorithm here in detail because the affectivity of application of this method was not supported by practice yet. For the similar reasons we do not describe here the details of the case 5 history that can be found in

The area limited by the polygon is the area of the seismic gap of the second kind.

**4.5.2 Methodology** 

(Tikhonov, 2009).

Fig. 21. Sketch showing a change of the coast-line occurred near Nevelsk as a result of the 2 August 2007 earthquake. a – position of the coast-line before the earthquake, b – uplifting portion of the sea-bottom after the earthquake; river Kazachka is shown as a black line.

#### **4.4.5 Case 4 summary**

In the case of the 2006 Gornozavodsk and the 2007 Nevelsk earthquakes the whole spectrum of prognoses from the long-term prediction to the short-term prediction of the 2007 Nevelsk earthquake was put into effect. The situation after the 2006 Gornozavodsk earthquake was interpreted correctly; the 2006 Gornozavodsk earthquake was treated as a foreshock of the stronger event. The short-term prediction was done for 7.5 months, but the 2007 Nevelsk earthquake had occurred three months later.

In case 4 the method of self-developing processes had resulted in an unexpectedly exact (Fig. 18) but maybe non-robust prognosis. The M8 algorithm was not applied in this case because of deficiency of data length for adjusting of the algorithm (the background level).

More details concerning the case 4 histories can be found in (Levin et al., 2007; Tikhonov, 2006; Tikhonov & Kim, 2010).

#### **4.5 Case 5 - Unsuccessful intermediate-term prediction of a great earthquake at Southern Kuril Islands**

#### **4.5.1 Seismic region and data**

This region includes the Urup, Iturup and Kunashir Islands (Fig. 22). The data used in earthquake forecasting were taken from the NEIC/USGS catalogues and contain earthquake data from December 1995 until December 2007; events with M 4.0 were taken into account as presumably registered without admissions.

Fig. 22. Map of earthquake M ≥ 5.9 epicenters near Kuril Islands, May 1999 – January 2010. The area limited by the polygon is the area of the seismic gap of the second kind.
