Simultaneous assessment of the median annual seismicity rates and their dispersions for Taiwan earthquakes in different depth ranges

Autor: Kuei-Pao Chen, Wen-Yen Chang, Yi-Ben Tsai
Rok vydání: 2017
Předmět:
Zdroj: Journal of Asian Earth Sciences. 135:136-154
ISSN: 1367-9120
DOI: 10.1016/j.jseaes.2016.12.027
Popis: The main purpose of this study is to apply an innovative approach to assess simultaneously the median annual seismicity rates and their dispersions for Taiwan earthquakes in different depth ranges. In this approach an alternative Gutenberg-Richter (G-R) relation is explicitly expressed in terms of both the logarithmic mean annual seismicity rate and its standard deviation, instead of only by the arithmetic mean in the conventional G-R relation. Seismicity data from 1975 to 2014 in a Taiwan earthquake catalog with homogenized M w moment magnitudes are used in this study. This catalog consists of high-quality earthquake data originally obtained by the Institute of Earth Sciences (IES) and the Central Weather Bureau (CWB). The selected seismicity data set is shown to be complete for M w ⩾ 3.0 . The logarithmic mean annual seismicity rate and its standard deviation from the observed annual seismicity rates of individual years are obtained initially for different M w ranges. It is shown subsequently that the logarithmic annual seismicity rates indeed possess a well-behaved lognormal distribution. It is further shown that our new approach has an added merit that tends to suppress the influences of anomalously high annual seismicity rates due to large numbers of aftershocks from major earthquake sequences. Finally, the observed logarithmic mean annual seismicity rates with their standard deviations for 3.0 ⩽ M w ⩽ 5.0 are used to obtain the alternative Gutenberg-Richter relations for different depth ranges. The results are as follows: log 10 N = 5.75 - 0.90 M w ± ( 0.25 - 0.01 M w ) for focal depth 0–300 km; log 10 N = 5.78 - 0.94 M w ± ( 0.20 + 0.01 M w ) for focal depth 0–35 km; log 10 N = 4.72 - 0.89 M w ± ( - 0.08 + 0.08 M w ) for focal depth 35–70 km; log 10 N = 4.69 - 0.88 M w ± ( - 0.47 + 0.16 M w ) for focal depth 70–300 km. In above equations log 10 N represents the logarithmic annual seismicity rate. These G-R relations give distinctly different values of the parameters a and b for Taiwan earthquakes in different depth ranges. These analytical equations can be readily used to obtain both the mean logarithmic annual seismicity rate and its standard deviation for any given M w . As an example, a numerical table presenting the corresponding median annual seismicity rates and their upper and lower bounds at median ± one standard deviation levels, is given at the end. This table offers a concise glance at the annual seismicity rates for Taiwan earthquakes of various magnitudes and focal depths. It is interesting to point out that the seismicity rate of crustal earthquakes, which tends to contribute most hazards, accounts for only about 74% of the overall seismicity rate in Taiwan. Accordingly, direct use of the entire earthquake catalog without differentiating focal depth ranges may result in substantial overestimates of potential seismic hazards.
Databáze: OpenAIRE
Externí odkaz: