**4.5.2 Methodology**

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

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.

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

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,

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

**4.5 Case 5 - Unsuccessful intermediate-term prediction of a great earthquake at** 

**4.4.5 Case 4 summary** 

2006; Tikhonov & Kim, 2010).

**Southern Kuril Islands 4.5.1 Seismic region and data** 

earthquake had occurred three months later.

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 (Tikhonov, 2009).

Current State of Art in Earthquake Prediction, Typical Precursors and

**5. Discussion and conclusion** 

Experience in Earthquake Forecasting at Sakhalin Island and Surrounding Areas 73

The analysis of behavior of seismicity within the generalized vicinity of large earthquake gives possibility to verify and to detail the characteristic parameters of the fore- and aftershock sequences and a number of other anomalies inherent to a vicinity of strong events (Rodkin, 2008). It was confirmed that the averaged fore- and aftershock cascades do obey the power law evolution. Power-law exponent of the foreshock cascade was found to be less than that of the aftershock cascade, and thus, the rate of increase of foreshocks number toward the moment of occurrence of the main event is slower than the rate of aftershocks decays. The typical duration of the aftershock process for M7+ events is about 100 days, while the average duration of the foreshock cascade in the constructed generalized vicinity was found to be quite noticeable during 10-20 days. The confirmation of a power law evolution for both fore- and aftershock cascades testifies that large earthquakes can be examined in terms of the critical phenomena. In this case it can be expected that the process of strong earthquake occurrence will be accompanied by other anomalies with a critical-like character of behavior. And factually, in parallel with the power-law fore- and aftershock cascades a stress-strain instability was shown to take place in the generalized vicinity of strong earthquake (see (Rodkin, 2008) for a more detailed description of these anomalies). It is worth mentioning also that much weaker increase in a number of events and the process of softening were revealed in a broader (few hundred days) time vicinity of a large

earthquake beyond the domain of the fore- and aftershock cascades occurrence.

be substantially less certain. It does take place actually.

the corresponding main shock.

earthquakes can be forecasted despite the shortage of available data.

The set of precursory anomalies indicates the approaching of a strong event quite definitely. Thus one can conclude that the effective short- and intermediate-term earthquake forecasting appears to be possible in the case of an essential increase of volume of statistical information available for forecasting. Now in every particular case of earthquake forecasting the volume of available information is much less than it is available in the generalized vicinity of strong earthquake, and correspondingly the results of forecasting are expected to

The state of art in a practice of earthquake forecasting is presented by an example of earthquake forecasting performed for the Sakhalin Island and the surrounding areas in the Institute of Marine Geology and Geophysics of the Far East Branch of the Russian Academy of Science, Yuzhno-Sakhalinsk, Russia. In two cases (1 and 4) from the five described above the whole set of earthquake parameters were successfully forecasted and thus these cases satisfy the term of "earthquake prediction". This practice suggests that at least in some cases

All the used algorithms of earthquake forecasting are based upon the general properties of seismic regime in vicinity of strong earthquake. These properties (besides the seismic quiescence) are similar with those revealed in the generalized vicinity of strong earthquake. The "seismic quiescence" was not found in the generalized vicinity of strong earthquake because of anisotropic character of this type of precursor anomaly in relation to epicenter of

We expect that the precursor features of the seismic regime behavior revealed in the generalized vicinity of strong earthquake can be useful in an earthquake prediction. These typical anomalies can be used as ideal images of precursory anomalies developing in process of preparation of individual strong earthquakes. Having in mind the volume of data
