Abstract
According to the 2020 FEMA Fact Sheet (FEMA, 2020), Puerto Rico and
Virgin Islands are located in a high risk region for earthquake damage.
In the last year (05-jul-2019 to 05-jul 2020) the Puerto Rico Seismic
Network (PRSN) recorded 136 earthquakes with magnitudes greater than 4.0
and two events had magnitudes greater than or equal to 6.0. The last
update of the seismic hazard maps for Puerto Rico and the US Virgin
Islands was performed in 2003. According to Mueller et al. (2010), the
Bunce fault, the Muertos Trough and related fault structures were not
included in the hazard map. The Great Southern Puerto Rico fault, was
considered largely quiescent, but Piety et al. (2008) through
paleoseismic studies, evidenced activity in this one. Otherwise,
offshore faults in southern Puerto Rico were not considered, because
their rates of activity were poorly known and assumed to be most likely
small. However, starting in December 2019 the Southwestern Puerto Rico
(SWPR) Seismic Sequence has been active and continues to be active in
these southern offshore faults. According to the StEER technical report
(Miranda et al., 2020), the events that occurred between December 2019
and January 2020 caused damage to approximately 10,000 structures and
more than 8,000 people were displaced. Based on these facts, and
considering that previously unknown tectonic fault structures have been
revealed by the SWPR Seismic Sequence (Lopez et al., 2020b), a
reevaluation of the seismic threat to Puerto Rico is required. This
should include the seismic activity that, according to the PRSN catalog,
consists of more than 50,000 events since 2002 to date. This new seismic
hazard evaluation will include multiple earthquakes with magnitudes
greater than M 5 which were not part of the catalog in 2001. The purpose
of this study is generating a new Ground Motion Prediction Equation
(GMPE) that incorporates the current seismicity for the region, which
unlike the local model used in Mueller et al. (2010) the data will be
used directly to obtain the ground motion relationships (Motazedian et
al., 2005). This new data now permits to obtain a GMPE from a regression
analysis. In the first stage of the research, the aim is generating a
preliminary GMPE based on crustal seismicity (events less than 25 km
deep) which represents more than 60% of the total registered
earthquakes in the PRSN catalog.