Seafloor morphology along the active margin in Guerrero, Mexico: Probable earthquake implications

Highlights

• The presence of forearc basins on the active continental margin in Guerrero, Mexico, is related to seamount subduction.

• The sediment thickness along the trench varies due to the presence of seamounts obstructing sedimentary input along the trench.

• Changes in sediment thickness along the trench may increase friction in the individual segments of the subduction zone.

• Seamount subduction in the GSG could potentially trigger earthquakes of Mw ~ 7.5.

Abstract

Submarine geomorphic features on the active margin along the Mexican Pacific coast are the result of subduction process. We analyze bathymetric data and present an overview of the continental slope geomorphology in the Guerrero seismic gap. For the first time we identify and describe submarine landforms in this area, including small-scale forearc basins, trench basin segmentation, narrow accretionary wedge and seamounts. We propose that the presence and formation of forearc basins are related to seamount subduction as well as the origin of higher relief above subducted seamounts. Here, forearc basins and trench sediments are sourced from submarine canyons. Notably, the thickness of sediments along the trench changes due to the presence of seamounts. Some parts of the trench seem to contain little sedimentary fill, which may increase friction along these segments of the subduction zone.

Introduction

Recent advances in technology and opening of free bathymetric data for several areas of the oceans seafloor provide a unique opportunity to analyze offshore morphology and bring light into the evaluation of earthquake and tsunami hazards. Open bathymetric data are even most valuable in areas where detailed bathymetric and geophysical data are lacking or access is restricted. Our detailed analysis of these public data reveals overlooked geomorphic features including seamount subduction in the Guerrero seismic gap. Although the debate on the relationship between subducted seamounts and seismicity is still ongoing (e.g. Basset and Watts, 2015a; Bell et al., 2014; Collot et al., 2017; Ruh et al., 2016; Sallares et al., 2013; Scholz and Small, 1997; Singh et al., 2011; Wang and Bilek, 2014; Yang et al., 2012), both seismic faulting and aseismic slip are considered to be related to seamount subduction (e.g. Watts et al., 2010; Clarke et al., 2018).

The Guerrero seismic gap (GSG), located along the Mexican subduction zone, has been investigated for a few decades, and the possible occurrence of high-magnitude earthquake and tsunami events in the near future is still under consideration (e.g. Kostoglodov et al., 2003; Ramírez-Herrera et al., 2007; Ramírez-Herrera et al., 2011). The deep-sea morphology in the GSG zone has not been explored and the seismic and tsunami hazards cannot be completely evaluated without knowledge of seafloor morphology. In this study, we analyze seafloor geomorphic features of this segment of the Mexican subduction zone and reevaluate their implications into earthquake and tsunami hazards along the coast using a compilation of available bathymetric data. Unlike published research focusing on data from the onshore subduction zone suggesting low seismic hazards in the region of the GSG (Husker et al., 2017), this paper focuses on the offshore zone between the trench and the coastline with the intention of and providing new data on the offshore tectonic framework. It is the first study of its kind in the GSG. This is a new important piece of puzzle in understanding seismic and especially tsunami hazard in the offshore area (e.g. Simons et al., 2011; Fan et al., 2017), alongside with previous works focused on slab geometry and/or seismicity (e.g. Suárez et al., 1990; Graham et al., 2016), and paleoseismological studies onshore (e.g. Ramírez-Herrera et al., 2007, 2009, 2012).

The GSG lies in an area of subduction-related tectonics where the Cocos plate subducts beneath the North American plate slightly oblique to the trench normal (9–14°; Gaidzik et al., 2016) and with a speed of subduction increasing from northwest (64 mm/year) to southeast (66 mm; DeMets et al., 2010). This area is a part of the Mexican active margin, along which tectonic erosion is known to be an important process at least during the last 20 m. y. (Clift and Vannucchi, 2004). The GSG does not record an earthquake since 1911 (Anderson et al., 1989; Kostoglodov and Ponce, 1994) and an earthquake of estimated Mw 8.2 magnitude is expected according to Anderson et al. (1994).