Slip Rate Determination of the Punta Montalva Fault in Southwestern Puerto Rico using LiDAR Data.

The Punta Montalva Fault in southwestern Puerto Rico is a left-lateral strike-slip fault that appears to warrant a more in-depth evaluation regarding the faults slip rate, how the fault is slipping, and overall length of the fault. First recognized through geological mapping of the Guánica Quadrangle in 2009, steeply inclined Miocene Ponce Limestone and a displaced stream and stream valley (~200 m) gave evidence to the NW-SE striking fault. A recent seismic sequence in southwestern Puerto Rico that began on December 28th, 2019 produced a M 6.4 earthquake on January 7th, 2020. Analysis of the focal mechanisms and space observations revealed part of the Punta Montalva Fault experienced 8 cm of left-lateral slip at the surface. Using a Miocene age for the Ponce Limestone and the displacement along the displaced stream, a minimum slip rate of 0.018-0.04 mm/yr can be inferred along the Punta Montalva Fault. However, little information is available regarding the Punta Montalva Fault. Outstanding questions for the Punta Montalva Fault include (1) how fast the fault is accommodating slip, (2) is the fault slipping seismically, aseismically sliding or both, and (3) what is the length of the faults spatial extent on the surface and at shallow bathymetry? Determining how fast the Punta Montalva Fault is accommodating slip is important to further indicate the regional strain rate of the area, which could help determine if the area has an increased hazard for large earthquakes. Light detection and ranging (LiDAR) data from the years 2004 and 2018 were used to produce digital elevation maps and to detect spatial change in the fault area using vertical and 3-D topographic differencing in attempt to constrain the slip rate at the surface of the Punta Montalva Fault. The 2004 and 2018 LiDAR datasets were manipulated through the LAStools software in preparation of the vertical and 3-D topographic differencing. Manipulation of the data includes assigning the same grid and coordinate system, eliminating noise, re-classifying points, and creating a digital terrane model and a digital surface model for each dataset. Preliminary results show spatial change that may be due to mass wasting and cultural artifacts. However, further noise reduction, and classification of points may provide a detection of slip at the fault trace.