41 Recent Advances in the Gulf of California Oblique Rift: Offshore and Onshore Studies // Avances Recientes en el Rift Oblicuo del Golfo de California: Estudios Marinos y Terrestres (Part III)

This session highlights recent research on the Gulf of California–Salton Trough plate boundary from ~12 Ma to today. We welcome terrestrial and marine studies involving tectonics, basin analysis, volcanology, sedimentology, and more. English or Spanish.

Friday, 24 April 2026
1:30 PM - 5:30 PM
LMH, Fiesta Terrace Salon

A Strike-Slip Earthquake that shouldn’t have made a Tsunami? The 1810 Loreto, Baja California, Event

Paper number: 41-9
Program: Technical Sessions
Time: 4:15 PM – 4:35 PM

Authors

Abstract

Historical documents indicate that on 27 August 1810 an earthquake affected the town of Loreto and the surrounding region along ~200 km of the Baja California coast, Mexico, producing considerable damage from strong ground motions. Unlike most nineteenth- and twentieth-century earthquakes in the region, the 1810 Loreto event generated extensive tsunami flooding along the eastern coast of Baja California, from Loreto to La Paz. Here we synthesize historical accounts of the event and evaluate the tectonic and geomorphic processes responsible for tsunami generation.

Based on historical observations and the regional tectonic framework, we interpret the earthquake as having occurred on a right-lateral, strike-slip transform fault, the Farallón fault, within the Gulf of California plate boundary system. The associated tsunami was disproportionately large relative to the reported earthquake intensity (IX), estimated magnitude (Mw 7.4), and the expected tsunami efficiency of strike-slip faulting. In addition, the tsunami arrival time, approximately one hour after the mainshock, is inconsistent with direct coseismic seafloor displacement, indicating that tsunami generation was decoupled from the primary fault rupture.

We integrate historical constraints with numerical tsunami modeling to test alternative source mechanisms, including direct generation by the earthquake and generation by a submarine landslide triggered by strong ground shaking. Modeling results show that the earthquake-only scenario cannot reproduce the documented inundation extent and delayed arrival time, whereas a submarine landslide source provides a closer match to historical observations.

These results support a model in which the 1810 Loreto earthquake triggered submarine slope failure that acted as the primary tsunami source. Ongoing work in coastal paleoseismology and archaeoseismology will further constrain earthquake and tsunami potential along the eastern margin of Baja California and improve assessments of coupled tectonic and surface processes in the Gulf of California.

Geological Society of America Abstracts with Programs. Vol. 58, No. 3

doi: 10.1130/abs/2026CD-410781

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