Geometry and Segmentation of the Philippine Fault in Surigao Strait

Bryan J Marfito,Deo Carlo E Llamas,Mario A Aurelio

doi:10.3389/feart.2022.799803

Bryan J Marfito, Deo Carlo E Llamas + Show 1 more

Open Access

https://doi.org/10.3389/feart.2022.799803

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Abstract

On 10 February 2017, a MS 6.7 earthquake, whose epicenter was located in Surigao Strait, struck the province of Surigao del Norte, causing numerous geologic impacts and damages to infrastructure. Field investigation conducted immediately after the earthquake revealed an NNW-SSE-striking surface rupture that extends 4.1 km inland. The remaining 20 km of the surface rupture, based on the computed magnitude-surface rupture length empirical relationship, was inferred to be located offshore along the Philippine Fault in Surigao Strait. We investigated the geometry of the fault in Surigao Strait by identifying morphotectonic features and geologic structures using offshore geophysical data that include multibeam bathymetry, sub-bottom profiles, and seismic reflection profiles. We interpreted several fault-related features such as pull-apart basin, offset channels, linear valleys, and folds and identified four fault segments, which are named the Maka-andog Strand, Surigao-Sanghid Strand, West Sanghid Strand, and Panaon Strand. Based on fault length, these segments are capable of generating MW 6.4 to 6.9 earthquakes. We have determined that surface rupture most probably extends along the entire length of the Surigao-Saghid Strand that generated the 2017 MS 6.7 earthquake. The identified morphotectonic features, presence of strike-slip with significant normal displacement in offshore geophysical imaging data, and focal mechanism all suggest that Philippine Fault in Surigao Strait is dominated by transtensional deformation, which supports the interpretations by previous authors.

Highlights

Earthquakes in the Philippines are generated by the movements of active faults and trenches which bound and straddle the archipelago
The fault traverses the offshore slope along the coast of San Juan, Southern Leyte it continues for 4.1 km inland that ruptured during the 2017 M6.7 earthquake
The results indicate that the Philippine Fault in Surigao Strait starts from the southern coast of Leyte, which is located south of the Cabalian volcano, up until the coast of Surigao del Norte

Summary

Introduction

Earthquakes in the Philippines are generated by the movements of active faults and trenches which bound and straddle the archipelago. Between 1988 and 2003, major earthquakes in the Philippines claimed 1,385 lives and cost approximately PhP34.94 billion worth of damages to private and public infrastructures and properties (World Bank, 2005). One such major earthquake generator is the Philippine Fault, which is a left-lateral active fault traversing Northern Luzon southward to Eastern Mindanao (Allen, 1962; Morante, 1974; Hirano et al, 1986; Quebral et al, 1996; Aurelio et al, 1997b; Tsutsumi and Perez, 2013; Perez et al, 2015; Rimando and Rimando, 2020). The high investment cost of offshore geophysical and geological equipment inhibits the widescale gathering of offshore data

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