Earthquakes triggered by the solid earth tide
Speaker: Ling-Yun Chang
Abstract
Tanaka et al .(2004) observe tidal triggering of earthquakes by measuring the correlation between the Earth tide and earthquake occurrence. This study used the earthquake catalog of the Japan Meteorological Agency (JMA) from October 1997 to May 2002. They statistically compared the azimuthal distribution of a tidal stress compressional component obtained for the observed earthquake occurrence with that synthesized for random earthquake occurrence in 100 subregions. The result confirms a significant difference between the observed and random catalog for 13 subregions. For these subregions, earthquakes preferentially occur when the tidal compressional stress is near the direction of P-axes of focal mechanisms obtained in corresponding subregions. This suggests that tidal stress may encourage earthquake occurrence when it act in the direction to increase the regional tectonic stress, but why can we not see a seismic response to the ubiquitous and predictable tides? Stein (2004) thought there might be two reasons. One is the stress might be too weak and lies below a threshold and another reason might be that the tidal oscillations are too brief to nucleate abundant earthquakes. Although the result of Tanaka et al. (2004) seems good, the tidal effect is evident in only 13%. Hence, if we want to monitor earthquakes by tidal stress, there are many parameters must be checked.
Reference
Tanaka, S., M. Ohtake, and H. Sato, Tidal triggering of earthquakes in Japan related to the regional tectonic stress. Earth Planets Space, 56, 511-515, 2004.
Ross S. Stein, Tidal triggering caught in the act. science, 305, 1248-1249, 2004.
Tanaka, S., M. Ohtake, and H. Sato, Evidence for tidal triggering of earthquakes as revealed from statistical analysis of global data, J. Geophys. Res. , 107 (B10), 2211, doi:10.1029/2001JB001577, 2002b.