**7. Conclusion**

80 Earthquake Research and Analysis – Seismology, Seismotectonic and Earthquake Geology

We have analyzed number of formulae for determination of paleoseismic catastrophes' magnitudes according to parameters of seismic rupture, published by different investigators: V.P. Solonenko and V.S. Khromovskikh (1978), A.A. Nikonov (1984) and D.L. Wells and K. J. Coppersmith (1994). Let's investigate their formulae for magnitude assessment by a length of the seismogenic rupture expressed in the surface and check these results on measured parameters of the fault scarps and an instrumental magnitude of the Tien Shan's Suusamyr earthquake of 1992 occurred in the depression with the same name

During the earthquake in the surface there were occurred only two short seismogenic ruptures with a total length of 4 km, a distance between then was 26 km (Bogachkin et al., 1997). A magnitude assessed instrumentally was Мs = 7.3. As it was discussed above at a description of the Suusamyr earthquake, in this case we have a deal with so-called "blind" seismogenic rupture, larger part of which did reach the surface. Let's assume that the total


M = 0.6 lg L + 6, we got М = 6.89.

M = 6.61 + 0.55 lg L, we got М = 7,42.

M = 5.08 + 1.16 lg L, we got М = 6.79. Cited above calculations show that the data by V.P. Solonenko and V.S. Khromovskikh (1978) on earthquakes parameters of the Baykal Lake and Caucasus regions, as well as world data by D.L. Wells and K.J. Coppersmith (1994) give underestimated magnitude of the earthquake if compare with the instrumental value. At the same time the formula by A.A. Nikonov (1984), calculated by him for earthquakes of the Central Asia gives a value which only on 0.1 higher than an instrumental value. This is a very good result especially if we are taking into an account that an accuracy of magnitudes determination by such method is in bounds of ±0,5 of the magnitude unit. This is why in our magnitudes assessments we based on formula by A.A. Nikonov (1984), which he specially deduced for

Our calculation (Table 6) have shown that according to paleoseismological data along the Talas-Fergana Fault zone there are possible earthquakes with magnitude М>7, and during unification of many segments (up to 11) a maximum magnitude can reach М=8. One can not exclude however that along the fault zone there were occurred two or more independent earthquakes divided by short time intervals. This interval we can not reveal because of significant miscalculations of Radiocarbon method of dating. It is possible that there were a clustering of the earthquakes along the seismogenic zone. In a history of strong earthquakes of the Tien Shan such clustering took place in the end of XIX – beginning of XX centuries. Here along so-called Northern Tien Shan Seismic Zone during only 26 years there were occurred 4 strong earthquakes: Belovodsk one of 1885 with МLH = 6,9; Verny earthquake of 1887 with МLH = 7,3; Chilik one of 1889 with МLH = 8,3 and Kebin earthquake of 1911 with

(Bogachkin et al., 1997).

length of the rupture (L) was 4 + 26 km = 30 km.



Baykal Lake and Caucasus regions):

a territory of the central Asia.

