Earthquake Ruptures on Complex Fault Systems: Insights from Haiti

Susan E. Hough, Stacey Martin, Steeve J. Symithe, & Rich Briggs

Submitted September 11, 2022, SCEC Contribution #11961, 2022 SCEC Annual Meeting Poster #007

We review historically observed earthquakes in Haiti, which has experienced two M 7+ earthquakes in the 21st century and a series of large earthquakes in the 18th century. Detailed rupture processes can rarely be established for historic earthquakes, but new investigations (Martin and Hough, BSSA, 2022; Hough et al, BSSA, 2022) rely on primary archival sources to characterize the shaking distributions of the 1860 Jour de Pâques sequence and 1770 earthquake. Preferred rupture scenarios are developed using modern ground motion models and ground motion-intensity conversion equations. For the 1860 sequence, Haitian newspapers provide more detailed macroseismic data than considered in previous studies, permitting identification and analysis of 3 damaging events. For the 1770 sequence, several French reports were published in Paris within a few years of the earthquake; these reports and a report from Léogâne provide detailed descriptions of the earthquake and damage. The results of Hough et al. (2022) support the interpretation that the 1770 earthquake was the largest documented earthquake on the Enriquillo Plantain Garden Fault (EPGF), zone with estimated M 7.6. Their preferred rupture scenario extends from east of Port-au-Prince to the west along the peninsula, terminating near Miragoâne Pond. This pond is within a left-stepping releasing bend along the EPGF zone, ~75 km WSW of Port-au-Prince. Part of the 1770 rupture may have been associated with overthrusting of the Massif de la Selle. Under this scenario, the observed event west of the Miragoâne pull-apart basin (St. Fleur et al., Tectonophysics, 2020) was likely associated with one or more prehistoric earthquakes. Martin and Hough (2022) conclude that the 1860 sequence released appreciable strain near the Miragoane pull-apart, in the gap between the 2010 and 2021 earthquakes, providing an explanation for why these two rupture zones were not contiguous. The Miragoâne pull-apart thus emerges as a candidate earthquake gate. The results further suggest that the 2010 and 2021 earthquakes together released less total moment than the 1770 earthquake. The 2010 earthquake may have occurred on the same fault(s) that ruptured in the 1770 earthquake or on one or more nearby subparallel faults. Results thus support the paradigm that earthquake gates control rupture segmentation, but ruptures on a complex fault are controlled by a combination of fault zone structure, dynamic processes, and prior rupture history.

Key Words
Earthquake gates, historical seismology

Hough, S. E., Martin, S., Symithe, S. J., & Briggs, R. (2022, 09). Earthquake Ruptures on Complex Fault Systems: Insights from Haiti. Poster Presentation at 2022 SCEC Annual Meeting.

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