Seismic Imaging of Megathrust Fault Properties and Forearc Structure Along and Across the Middle America Subduction Zone, Offshore Mexico

Ward, Grace (2027) Seismic Imaging of Megathrust Fault Properties and Forearc Structure Along and Across the Middle America Subduction Zone, Offshore Mexico. Masters thesis, Northern Arizona University.

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Abstract

Slow slip events (SSEs) are an important but poorly understood type of slip at subduction zones. It remains unclear what physical conditions promote the occurrence of slow slip versus earthquake slip on plate boundary faults. The Guerrero segment of the Mexico Subduction Zone (MSZ) has experienced both deep and shallow slow slip events but has not hosted a large megathrust earthquake in ~115 years. In contrast, adjacent segments regularly rupture in Mw>7 earthquakes. To investigate the architecture and physical properties of the Mexico subduction zone across areas that experience different slip behavior, we analyzed multi-channel seismic (MCS) reflection data from the 2022 ¡Me Gusta! expedition. Two seismic profiles were examined: a trench-perpendicular profile crossing the subduction zone SE of the Guerrero Gap near Acapulco (Line 3) and a trench-parallel forearc profile extending across the Guerrero Seismic Gap (GSG) and adjacent segments (Line 4). Seismic reflection imaging reveals that the shallow plate boundary offshore Acapulco is relatively smooth and laterally continuous despite the presence of bending faults and seamounts on the incoming Cocos Plate. Trench sediments are thin (~200 m) and appear to be largely accreted into a small frontal prism rather than subducted. A highly reflective plate interface extends ~18 km landward of the trench and to depths of ~8 km before becoming less reflective at greater depths. Reflection coefficient estimates derived from pre-stack shot gathers range from ~0.11 to 0.25, which can be explained by the impedance contrast between the accretionary prism and oceanic crust. Along-strike variations observed on Line 4 show enhanced reflectivity beneath the northwestern portion of the GSG, coinciding with regions previously interpreted to host SSEs associated with thicker gabbroic crust and elevated pore-fluid pressures. This study reveals along-strike and downdip variations in plate boundary reflectivity that sometimes coincide with changes in megathrust slip behavior along the MSZ, but the correlation is not consistent, suggesting that additional methods are needed to examine controls on slip behavior.

Item Type:	Thesis (Masters)
Keywords:	Slow slip events; Guerrero segment; Mexico Subduction Zone; Earthquakes; Plate boundaries
Subjects:	Q Science > QE Geology
NAU Depositing Author Academic Status:	Student
Department/Unit:	College of the Environment, Forestry, and Natural Sciences > School of Earth Sciences and Environmental Sustainability
Date Deposited:	07 Aug 2026 18:08
Last Modified:	07 Aug 2026 18:08
URI:	https://openknowledge.nau.edu/id/eprint/6363

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