The Miragoâne seismic clusters in southern Haiti triggered by the Mw 7.2 Nippes earthquake of August 14, 2021

On August 2021, 14^th, a Mw 7.2 earthquake struck Haiti’s southern peninsula, eleven years after the devastating Mw 7 January 12, 2010 earthquake that occurred near Port au Prince. This large event, called the Nippes earthquake, has been recorded locally by the citizen network composed of low-cost raspberry shake stations. A precise analysis of the mainshock rupture from geodetic and seismic data revealed both left lateral strike slip and trust motion.

Few days after the mainshock, a temporary network consisting of 12 broadband stations was deployed in the vicinity of the epicentral zone in order to better record the aftershock sequence. Data from August 20 to December 31, 2021, were used to determine a suitable 1D velocity model of the zone and relocate about 2500 aftershocks that highlight the activation of several structures.

In this study, we focus our analysis on the region of Miragoâne situated between the ruptures of the 2021 and the 2010 earthquakes.  Before the Nippes earthquake, only a few events were detected there. Then, the Nippes earthquake triggered a burst of seismicity that lasted two months and stopped on November 2, 2021 and resumed in January 14 until March 10, 2022 with the occurrence on January 24th of two earthquakes in less than an hour of magnitude 5.3 and 5.1 respectively. We use the new 1D velocity model and the NonLinLoc using Source-Specific Station Term Corrections method (NLL-SSST) to relocate this seismic sequence. We find that the two larger earthquakes of magnitude slightly greater than 5 are closely located and confirm their reverse faulting mechanism using the waveform inversion method FMNEAR. The relocated seismicity is distributed from the surface to 20 km deep between the coast and the Enriquillo left-lateral strike-slip fault and along a plane which dips southward at ~50°, in agreement with the reverse faulting mechanism of the two larger magnitude > 5 earthquakes.