Double-Difference Relocations of Foreshocks, Mainshock and Aftershocks Associated to the 2019–2020 Southwestern Puerto Rico Seismic Sequence

Session: Early Results from the 2020 M6.4 Indios, Puerto Rico Earthquake Sequence [Poster]
Type: Poster
Date: 4/30/2020
Time: 08:00 AM
Room: Ballroom
Description: 

We used Waldhauser and Elsworth (2000) double-difference technique in an effort to determine the fault plane of the rupture history of the Southwestern Puerto Rico seismic sequence that started on December 28, 2019. The variability of earthquake hypocenters in the region directly from the PRSN catalog suggest rupture in multiple faults, reminiscent of systems analogous to those of 2016 Amatrice-Norcia (Improta et al., 2019) and Kaikoura (Xu et al., 2018, Litchfield et al., 2018) events. The almost purely strike-slip focal mechanism of the M4.7 December 29, 2019 event computed by NEIC is in agreement with an offshore extension of the WNW-ESE trending left-lateral Punta Montalva fault mapped on-land by Roig et al. (2013). With a NE-SW trending normal focal mechanism, the Mw6.4 January 7, 2020 mainshock, is arguably the result of stress transfer from the offshore Punta Montalva fault to a northeast-trending normal fault. As the production of aftershocks continued along faults of parallel trends to either of these faults, questions started to arise about defining with a better degree of certainty the location of the faults. Using a variety of filters in HypoDD to define event pairs, we were able to preliminarily obtain double-difference relocations on a series of clusters defined by hypocenter separations. As the process of earthquake locations is on-going, we will present a relocation study based on all available events up to mid-April. Preliminary data of 900 events between December 29, 2019 until January 2, 2020 show tighter constraints on what appears to be the southeastern offshore extension of the Punta Montalva. However, the event pairs were only weakly linked and many events were filtered out due to low quality. The addition of the six USGS temporary real-time seismic stations and the five PRSN temporary stations is expected to provide better linkage among event pairs. The augmented number of events would help resolve stronger linkage among and thus hopefully provide a better definition of rupturing faults.

Presenting Author: Alberto M. Lopez

Authors