A strong and shallow earthquake registered by the USGS as M5.9 (downgraded from M6.0) hit southern Puerto Rico at 12:54 UTC (08:54 LT) on January 11, 2020. The agency is reporting a depth of 10 km (6.2 miles). The quake comes 4 days after shallow M6.4 -- the strongest to hit the island in 102 years. The region is experiencing intense earthquake swarm over the past two weeks, with 445 M2.5 earthquakes, 21 M4.5+ and 1 M6+.
The epicenter of today's M5.9 was located 13.8 km (8.6 miles) S of Indios (population 1 739), 15.4 km (9.6 miles) SE of Guanica (population 9 224), 18.8 km (11.7 miles) SSE of Yauco (population 20 295), 25 km (15.5 miles) SW of Ponce (152 634), 34.3 km (21.3 miles) SE of San German (12 055), Puerto Rico.
There are 2 800 000 people living within 100 km (62 miles).
217 000 people are estimated to have felt strong shaking, 335 000 moderate and 2 621 000 light.
The USGS issued a green alert for shaking related casualties and yellow for economic losses. Some damage is possible and the impact should be relatively localized. Estimated economic losses are less than 1% of GDP of Puerto Rico. Past events with this alert level have required a local or regional level response.
Overall, the population in this region resides in structures that are resistant to earthquake shaking, though vulnerable structures exist. The predominant vulnerable building types are mud wall and informal (metal, timber, GI etc.) construction.
Southern Puerto Rico earthquakes 14 days to January 11, 2020. Credit: Google, TW/SAM
This earthquake sequence is consistent with the expectations of seismicity in the region, the USGS said January 10.
Historically the region has seen moderate seismicity, but Puerto Rico is tectonically active, and infrequent naturally occurring large earthquakes are expected. Before this sequence, within the last 50 years and within 31 miles of the M 6.4 quake’s epicenter, there have been 10 earthquakes M 4.0+.
Estimated population exposure to earthquake shaking
Selected cities exposed
Featured image credit: Google, TW/SAM