講演情報
[P13-04]フィリピン南部ミンダナオ島における2023年内陸群発地震とその余震活動
マヌエル シエン1,2、*北 佐枝子1,3 (1. 政策研究大学院大学、2. フィリピン火山地震研究所、3. 国立研究開発法人 建築研究所 国際地震工学センター)
On March 6 to 7, 2023, three inland earthquakes occurred in Davao de Oro, Mindanao, southern Philippine with magnitudes ranging from Mw 5.3 to 5.9 (PHIVOLCS, 2023). The main events and aftershock sequence were found near the Leonard Kniaseff Volcano. The Philippine Institute of Volcanology and Seismology (PHIVOLCS) installed six temporary seismic stations for one month to monitor the aftershocks, obtaining an earthquake catalog for the observation period by joint fate of the temporary and routine seismic networks. This study aims to improve the catalog using a machine learning-based phase picker with a phase association and hypocenter location algorithm. Firstly, we applied the waveform data to the Phasenet (Zhu & Beroza 2019) in order to pick up arrival times of P-and S-waves. Secondly, we also performed the phase association process by the REAL (Zhang et al. 2019). Then, hypocenters are relocated at depths of 0 to 40 km by VELEST, improving the initial catalog with increase of number of events (from 154 to 437 events). The D95 is estimated as 27.402 km in the study area, which is almost the same value as that in southern Philippine by Sawi et al. (2023 EGU meeting) and deeper than that reported in Japan archipelago (~14km, Omuralieva et al. 2010). The improved earthquake catalog reveals that depths of hypocenters near the Leonard Kniaseff Volcano are shallower, whereas earthquakes farther from the volcano occurred deeper. This trend of depth distribution of hypocenters related with volcanic area has also been reported by a previous study for the 2019 Cotabato and Davao del Sur earthquake sequences near Mt. Apo in southern Philippine (Sawi et al. 2023 EGU meeting). These observation facts could imply that 1) high geothermal gradients around volcanoes limit the depth range of seismogenic zone in the crust. 2) the thermal structure in the southern Philippine is colder than that in Japan archipelago because of the double seismic plates beneath the southern Philippine. The catalog also reveals seismicity migration from deep to shallow depth, which could imply fluid migration. The catalog allows this interpretation of seismicity despite having limited time for observation.