← Back to Gallery

A High-Resolution View of the 2020 Puerto Rico Earthquake Sequence With Machine Learning

The unusually active 2020 Puerto Rico earthquake sequence, located just offshore in southwestern Puerto Rico, is still ongoing in January 2021. This sequence started on December 28, 2019 with a M4.7 strike-slip earthquake. The eventual M6.4 mainshock, an oblique normal fault earthquake, ruptured on January 7, 2020. One M6+, 15 M5+, 118 M4+, and 1,710 M3+ earthquakes have occurred since the sequence began.

To better understand the processes driving this sequence, I applied EQTransformer (Mousavi et al., 2020), a deep learning model trained on a global earthquake data set, to automatically detect earthquakes and pick P and S phases on continuous seismic data at 26 nearby stations during the time period 2018-01-01 to 2020-11-01. I then located all earthquakes with phase picks on at least 4 stations, using a 1D layered velocity model (Mendoza and Huerfano, 2005).

Deep learning models excel at identifying frequent small earthquakes, but they are not yet ready to completely replace standard earthquake monitoring methods. EQTransformer detected over 100,000 earthquakes in the Puerto Rico sequence; almost 90,000 of these earthquakes, mostly with magnitudes between 1 and 3, were not in the ComCat earthquake catalog. EQTransformer failed to detect about 2600 catalog earthquakes, including the M6.4 mainshock and several M>4 events.

The earthquake locations reveal activation of a complex fault system with a mix of normal and strike-slip faults, with a ~60-km east-west seismicity trend intersecting a ~40-km NE-SW seismicity trend. During the 2 weeks after the M6.4 mainshock, earthquakes occurred on both the east-west and NE-SW trends. Later, swarm-like migration of clustered seismicity occurred to the east in May 2020, then to the west in June-September 2020. Two small seismicity bursts before the sequence started, in December 2018 and December 2019, were located near the eastern edge of the subsequent earthquake sequence.

Presenting Author: Clara Yoon

Student Presenter: No

Day: 4/20/2021

Time: 11:30 AM - 12:30 PM Pacific

Additional Authors