Publication Date:
2009-06-01
Description:
We examine two closely located earthquakes in Japan that had identical moment magnitudes M (sub w) but significantly different energy magnitudes M (sub e) . We use teleseismic data from the Global Seismograph Network and strong-motion data from the National Research Institute for Earth Science and Disaster Prevention's K-Net to analyze the 19 October 1996 Kyushu earthquake (M (sub w) 6.7, M (sub e) 6.6) and the 6 October 2000 Tottori earthquake (M (sub w) 6.7, M (sub e) 7.4). To obtain regional estimates of radiated energy E (sub S) we apply a spectral technique to regional (〈200 km) waveforms that are dominated by S and Lg waves. For the thrust-fault Kyushu earthquake, we estimate an average regional attenuation Q(f)=230f (super 0.65) . For the strike-slip Tottori earthquake, the average regional attenuation is Q(f)=180f (super 0.6) . These attenuation functions are similar to those derived from studies of both California and Japan earthquakes. The regional estimate of E (sub S) for the Kyushu earthquake, 3.8X10 (super 14) J, is significantly smaller than that for the Tottori earthquake, E (sub S) 1.3X10 (super 15) J. These estimates correspond well with the teleseismic estimates of 3.9X10 (super 14) J and 1.8X10 (super 15) J, respectively. The apparent stress (tau (sub a) =mu E (sub S) /M (sub 0) , with mu equal to rigidity) for the Kyushu earthquake is 4 times smaller than the apparent stress for the Tottori earthquake. In terms of the fault maturity model, the significantly greater release of energy by the strike-slip Tottori earthquake can be related to strong deformation in an immature intraplate setting. The relatively lower energy release of the thrust-fault Kyushu earthquake can be related to rupture on mature faults at a subduction environment. The consistence between teleseismic and regional estimates of E (sub S) is particularly significant as teleseismic data for computing E (sub S) are routinely available for all large earthquakes whereas often there are no near-field data.
Print ISSN:
0037-1106
Electronic ISSN:
1943-3573
Topics:
Geosciences
,
Physics
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