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WITHDRAWN New Insights From Two 2022 Large Magnitude Earthquake Events Occurring Closely in Space and Time in Abra, Northern Philippines

Description: 

WITHDRAWN In the second half of 2022, the province of Abra in the island of Luzon, Northern Philippines was struck by two large magnitude earthquakes in a span of less than three months and within a 20-kilometer radius. On July 27, 2022, at 8:43 am (Philippine Standard Time), the area was struck by a magnitude Mw 7.0 earthquake that caused intense ground shaking. The epicenter was located at 17.64° N latitude, 120.63° E longitude, at a focal depth of 15 km. On October. 25, 2022, at 10:59 p.m. (PST), a magnitude Mw 6.4 earthquake struck the same area, at an epicenter located only about 18 kilometers northeast of the July earthquake epicenter, at the same focal depth of 15 km. Destruction in both earthquakes included collapsed residential and commercial buildings, structural damage in century-old heritage churches, government buildings, bridges and roads. Ground deformation included numerous landslides in the mountainous regions, and liquefaction in riverbeds and coastal areas. While infrastructure damage was significant, surface ground rupture was not evident after both earthquakes. The epicentral areas are known to be prone to earthquakes due to the presence of the Philippine Fault System (PFS) there. However, the focal mechanism solutions of the main shocks suggest gently-dipping fault planes which are not consistent with the known geometry of the PFS and its branches in the area. Instead the distribution of the aftershocks, nodal plane geometries, Coulomb Stress Transfer (CST) modeling and analysis by radar interferometry suggest that the earthquake-generating faults project surface ruptures located further west, following the location and trend of other PFS fault branches. These temporally and spatially closely-spaced July and October earthquakes pose new questions on the current knowledge about the PFS in northern Luzon, but also provide new insights that contribute in understanding the nature and earthquake behavior of complex fault systems, including fault asperities, post-earthquake stress transfer, seismic rate changes, aftershock evolution and earthquake triggering.

Session: New Observations and Modeling of Triggered Seismicity

Type: Oral

Date: 4/19/2023

Presentation Time: 05:15 PM (local time)

Presenting Author: Sandra Donna A. Catugas

Student Presenter: Yes

Invited Presentation: 

Authors