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Surface Rupture and Fault Characteristics Associated with the 2020 Magnitude (MW) 6.6 Masbate Earthquake, Masbate Island, Philippines
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  • Deo Carlo E. Llamas,
  • Bryan J. Marfito,
  • Ronald Dela Cruz,
  • Mario Aurelio
Deo Carlo E. Llamas
Philippine Institute of Volcanology and Seismology

Corresponding Author:[email protected]

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Bryan J. Marfito
Philippine Institute of Volcanology and Seismology
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Ronald Dela Cruz
Philippine Institute of Volcanology and Seismology
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Mario Aurelio
University of the Philippines Diliman
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The magnitude (MW) 6.6 earthquake that struck Masbate Island on 18 August 2020 offers a unique opportunity to investigate the slip and seismic behavior of the Philippine Fault in the Masbate region. In this study, we employ InSAR, seismicity analysis, and field investigations to comprehensively characterize the coseismic and postseismic slip associated with the event. Our findings reveal a 50-km-long fault rupture along the Masbate segment of the Philippine Fault, with ~23 km surface rupture mapped onshore, despite the occurrence of interseismic creep. The slip distribution demonstrates decreasing displacements northwestward towards the creeping section, with a maximum left-lateral displacement of 0.97 m near the epicenter. Toward the southeast offshore, the rupture terminates at a fault left stepover. While the surface rupture appears relatively straight and narrowly concentrated, the secondary ruptures and mapped offshore faults reveal a more complex transtensional fault structure in the vicinity of Cataingan Bay. This fault complexity represents an asperity that facilitates high-stress accumulation and rupture initiation. Postseismic slip persists for several months along the onshore creeping segment. We derived a slip rate of 2.8 to 4.3 cm/year from long-term and short-term slip measurements. Furthermore, we calculated a recurrence interval of 16 to 41 years for earthquakes similar to the 2020 Masbate earthquake.  Our study highlights how heterogeneity in fault properties, including geometry and coupling state, influences the distribution of slip and magnitude of earthquakes. The 2020 Masbate earthquake provides valuable insights into the rupture dynamics and fault behavior of the Philippine Fault in the Masbate region.
06 Oct 2023Submitted to ESS Open Archive
17 Oct 2023Published in ESS Open Archive