著者

飯塚 進

出版者

公益社団法人 日本地震学会

雑誌

地震 第2輯 (ISSN:00371114)

巻号頁・発行日

vol.29, no.4, pp.365-374, 1976

被引用文献数

1

---

There is a remarkable discrepancy in the previous results on the temporal variations in seismic wave velocities related with the Matsushiro earthquake swarm that have been studied by many investigators. A result from the <i>V_p</i>/<i>V_s</i> method shows co-seismic anomaly, while all the data from the P-residual method indicate precursory anomaly.<br>To make clear the cause of this discrepancy, temporal changes in <i>V_p</i>/<i>V_s</i> ratio was reexamined by using the different set of data source from previous studies. Two kinds of velocity anomalies, namely, precursory and co-seismic or post-seismic anomaly were detected as the same as in the previous investigations.<br>Combining the present data with the data from previous studies, it was inferred that the precursory anomaly in seismic velocities might occur mainly in the zone of lower crust to the uppermost mantle, while the co-seismic or post-seismic anomaly might occur in the upper part of crust whose depth is not greater than 10km, underneath at and adjacent area of the Matsushiro earthquake swarm. In other words, the anomalous zone must have migrated from the deeper parts to the upper crust about the time when the swarm began.<br>The origin of these two anomalies were interpreted by a new model which takes thermal effects into consideration for earthquake occurrences.