SEISMIC ANALYSIS OF A HIGH VELOCITY ANOMALY IN THE MONA BLOCK

The Puerto Rico Seismic Network’s (PRSN) current 1-D crustal structure velocity model is more than 20 years old. Since then, the PRSN has increased its detection capability by increasing station coverage and upgrading existing equipment. Analysts have observed that data from stations in the northwest region of Puerto Rico demonstrate consistently high travel time residual values for earthquakes located in the eastern side of the island and vice versa. To examine and quantify the anecdotal evidence of this behavior, travel-time curves, residual plots and ray path tracing calculations were generated. The dataset consisted of the events processed by the PRSN between 2010 to 2016 using eight seismic stations. This data was used to generate: Travel-time curves, Travel-Time residual plots, Ray paths combined with travel-time residual maps using PRSN’s velocity model (Huerfano and Bataille, 1994) concatenated to the IASP91 model (Kennett and Engdahl ,1991). Our previous work limited the dataset to solely shallow events and Pg raypaths. Here we expand on this work to include Pn paths and direct P paths from the local sudbducted slab as well as analysis of S-wave data. The addition of these raypaths will generate a full dataset for multidimensional modeling. Preliminary analysis of the data indicates that a high velocity anomaly lies within the Mona block (west of the Mona Rift canyon). One possible interpretation is that the rifting has generated a thinned crust beneath the Mona block. However, the study does not exclude mafic underplating.