Abstract
In the present study, the level of the largest earthquake hazard is assessed in 28 seismic zones of the NW Himalaya and its vicinity, which is a highly seismically active region of the world. Gumbel’s third asymptotic distribution (hereafter as GIII) is adopted for the evaluation of the largest earthquake magnitudes in these seismic zones. Instead of taking in account any type of Mmax, in the present study we consider the ω value which is the largest earthquake magnitude that a region can experience according to the GIII statistics. A function of the form Θ(ω, RP6.0) is providing in this way a relatively largest earthquake hazard scale defined by the letter K (K index). The return periods for the ω values (earthquake magnitudes) 6 or larger (RP6.0) are also calculated. According to this index, the investigated seismic zones are classified into five groups and it is shown that seismic zones 3 (Quetta of Pakistan), 11 (Hindukush), 15 (northern Pamirs), and 23 (Kangra, Himachal Pradesh of India) correspond to a “very high” K index which is 6.
Highlights
Earthquake hazard assessment of a region is the ultimate goal for geoscientists, which is a useful tool for the preparation of earthquake risk mitigation policies
A first inspection of Table 1 shows that, generally, the estimated Ȧ values and obs max values do not differ significantly. This is due to the fact that the estimation of the Ȧ parameter in most of the analyzed seismic zones is based on relatively long duration of earthquake data, which is comparable with the seismic cycle of the strongest earthquake in respective zones
We considered that the K index is a function of Ȧ values and RP6.0 and denoted as the term Ĭ(Ȧ, RP6.0)
Summary
Earthquake hazard assessment of a region is the ultimate goal for geoscientists, which is a useful tool for the preparation of earthquake risk mitigation policies. The first (GI) and the third (GIII) asymptotic distributions of extreme values (Gumbel 1958) have proven a useful tool in estimating earthquake hazard in different seismic regions, globally distributed. Both Gumbel’s distributions have the advantage that they do not require analysis of the whole data set used. These procedures require predetermined fix time intervals from which the largest earthquake magnitudes are selected. These arbitrary time intervals are usually based on the seismicity rate of the region under investigation. Båth (1973, 1975, 1983) suggested that the dependency of the method on the largest magnitudes is the principal advantage of the technique, given that the magnitudes of the largest events are more accurately determined than those of small shocks
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