Authors: Teresito Bacolcol, Alfie Pelicano, Genesis Sapla, Cassandra Cabigan, Alyssa Pariñas, Abegail Abrenica, Zachary Ragadio, Bon Morales, Alberto Baloto, Ken Villar, Nehemiah Manalaysay, Roderick Ramos, Patricia Belardo, Winchelle Ian Sevilla, and Kenneth Jhon Remo
Department of Science and Technology-Philippine Institute of Volcanology and Seismology (DOST-PHIVOLCS)
Download link: https://bit.ly/GPSMotions-2023-SurigaodelSur-Earthquakes
ABSTRACT: Two major offshore earthquakes struck the province of Surigao del Sur, Philippines – a magnitude (Mw) 7.4 on 02 December 2023 and a Mw 6.8 on 04 December 2023. Global Positioning System (GPS) data were analyzed to estimate long-term interseismic velocities and co-seismic displacements associated with these two events. Joint inversion of near-field GPS displacements with teleseismic body and surface wave was also conducted to estimate the finite fault solution of the 02 December 2023 event.
Long-term GPS data from 2008 to 2023 showed that the interseismic horizontal velocities in northern and eastern regions of Mindanao varied from 47.25 mm/yr to 72.83 mm/yr with azimuths between N282.42° to N298.56°, relative to the Eurasian Plate. Co-seismic horizontal displacements of 280.75 mm, 216.27 mm, and 199.49 mm were measured at campaign sites located 29 km, 53 km, and 57 km from the Mw 7.4 epicenter, respectively. The nearest permanent station to the Mw 6.8 epicenter recorded a horizontal displacement of 101.73 mm. Most of the points demonstrated eastward movement with subsidence, indicating an elastic rebound. Real time data from Velocity and Displacement Autonomous Solution Engine (VADASE) stations showed co-seismic displacements ranging from 54.72 mm to 290.70 mm for the Mw 7.4 event and 17.12 mm to 72.06 mm for the Mw 6.8 event. Ground shaking was detected at least 13 seconds following the Mw 7.4 earthquake and at least 31 seconds for the Mw 6.8 earthquake detected by a station located 105.29 km away from the epicenter. The finite fault model for the 02 December 2023 Mw 7.4 earthquake indicates a maximum slip of 1.81 m with the concentration of slip occurring between depths of approximately 16 km and 40 km.
Citation:
Bacolcol, T., Pelicano, A., Sapla, G., Cabigan, C., Pariñas, A., Abrenica, A., Ragadio, Z., Morales, B., Baloto, A., Villar, K., Manalaysay, N., Ramos, R., Belardo, P., Sevilla, W.I., and Remo, K.J. 2025 GPS Motions Associated with the December 2023 Offshore Surigao del Sur Earthquakes. PHIVOLCS Open-File Report No. 25-01, 19 pages.
