[S-CG39] Science of slow earthquakes: Toward unified understandings of whole earthquake process

[SCG39-22] Focal mechanism and radiated energy from shallow tremors in the Guerrero seismic gap.

*Raymundo Omar Plata Martinez¹、Yoshihiro Ito²、Kazuaki Ohta⁴、Masanao Shinohara⁵、Satoshi Ide³ (1.Graduate School of Science, Kyoto University、2.Disaster Prevention Research Institute, Kyoto University、3.Department of Earth and Planetary Science, University of Tokyo、4.National Research Institute for Earth Science and Disaster Resilience、5.Earthquake Research Institute, University of Tokyo)

キーワード：Shallow tremor, Guerrero gap, Slow earthquakes, Focal mechanism, Seismic energy

Thanks to the recent development of offshore seismic networks monitoring shallow slow earthquakes have been reported in different subductions zones, such as the case of the Japan trench, New Zealand and most recently the Guerrero seismic gap at the Mexican subduction. In Guerrero, a good understanding of deep slow earthquakes has already been acquired, on the contrary, shallow slow earthquakes in Guerrero have been scarcely explored. A better knowledge of the shallow slow earthquakes in the Guerrero seismic gap is necessary to characterize the seismogenic zone at the shallow plate interface. Shallow tremors in the Guerrero seismic gap were observed using data from an array of ocean bottom seismometers (OBS). We analyzed this data to estimate source parameters, such as focal mechanisms and radiated seismic energies of shallow tremors. OBS data includes attenuation and site effects, predominantly from an offshore environment, which needs to be understood to unmask source properties of seismic events recorded. After correcting horizontal orientation of OBS, focal mechanism of shallow tremors and regular earthquakes were calculated by inverting observed S-wave polarization angles. Focal mechanisms for both shallow tremors and regular earthquakes trend to follow the subducting plate motion with a low thrust angle. Additionally, spectral inversion with regular earthquakes was done to estimate site effects and attenuation for the OBS region. By removing these two effects, source spectrum of shallow tremors will be available for comparison with regular earthquakes in the region. Describing shallow tremors in the Guerrero the seismic gap will bring a new perspective of the seismic behavior of the Guerrero seismic gap.