Revised ML Determination for Crustal Earthquakes in Taiwan
Resource
Bulletin of the Seismological Society of America 95 (6): 2517-2524
Journal
Bulletin of the Seismological Society of America
Journal Volume
95
Journal Issue
6
Pages
2517--2524
Date Issued
2005
Author(s)
Abstract
Abstract The local magnitude scale M L is an empirically derived scale anchored to a zero magnitude reference event. Richter defined the amplitude of ground shaking at an epicentral distance of 100 km for a zero magnitude earthquake in southern California. The crustal attenuation characteristics of Taiwan result in a relatively high M L when compared to moment magnitude, M w. We therefore define a revised M L scale for crustal earthquakes in the Taiwan region that is more consistent with M w. Using observed peak ground shaking and M w, we determine a new log A 0 curve of ground shaking versus hypocentral distance, R, for a zero magnitude earthquake, and station correction factors. The log A 0 curve determined in this study is, log A (R) � 0.332 � 1.568 • log(R) � 0.280. 0 Using this new log A 0 curve and station corrections, the new M L is more consistent with M w, with a 0.2 magnitude unit uncertainty. The new log A 0 curve has a value of �2.80 at the distance of 100 km compared to the anchor point of log A 0 ��3 at the same distance as defined by Richter for southern California. This means that the current M L estimates in Taiwan (which use Richter’s definition) average 0.2 magnitude units larger than their M w. The station correction factors also determined are large, from �0.40 to 0.52 magnitude units. The use of station corrections in routine seismic network operation in Taiwan will improve magnitude estimates. This is particularly important for smaller events when recording stations may be predominantly on either hard rock or soft soil sites, which could lead to under- or overestimates of the magnitude by up to half a magnitude unit.
Type
journal article
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