Civil Insight: A Technical Magazine Volume 3 | Page 53

Shrestha P. et al.
Civil Insight (2019) 51-56
aftershock. After that, using the given dynamic algorithm, aftershocks were removed from the earthquake
catalog.
Table 1. Window Algorithm for aftershocks removal (Gardner & Knopoff, 1974)
Magnitude, 
2.5
3.0
3.5
4.0
4.5
5.0
5.5
6.0
6.5
7.0
7.5
8.0
Distance,  (km)
19.5
22.5
26.0
30.0
35.0
40.0
47.0
54.0
61.0
70.0
81.0
94.0
Time,  (days)
6.0
11.5
22
42
83
155
290
510
790
915
960
985
2.3) Seismic source zones
The encircled portion of the Fig. 2 below shows the seismic source within 300km of the dam site, which
was considered as a seismic source. The entire study area was further divided into 12 seismic source zones
with reference to Thapa and Wang (2013), as shown in Fig. 2.
Fig. 2. Seismic source zones around the dam site
2.4) Seismicity parameters
Gutenberg-Richter Recurrence Law (1944)
Gutenberg and Richter (1944) gathered a number of earthquake data for Southern California over a period
of many years and organized the data according to the number of earthquakes that exceeded different
magnitudes during that time period. They divided the number of exceedances of each magnitude by the
length of time period to define a mean annual rate of exceedance ɉ  of an earthquake of magnitude  .
Small earthquakes are frequent as compared to large earthquakes; therefore, ɉ  for small earthquakes is
greater than that for large earthquakes. The reciprocal of the annual rate of exceedance for a particular
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