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M=6.9 earthquake in Chile follows intense seismic swarm

Temblor

By David Jacobson and Volkan Sevilgen, Temblor

** Read about the seismic swarm that preceded this earthquake **

See earthquakes in Chile

Updated: 9:00 am PDT 25 Apr 2017

A M=6.9 earthquake shook Chile’s capital city of Santiago, just days after an earthquake swarm began offshore. (Photo from: flickr)

 

At just past 5:30 p.m. local time, a M=6.9 earthquake shook central Chile, including the capital city of Santiago (EMS reported the earthquake was a M=6.7). This earthquake’s epicenter was offshore of the port city of Valparaiso, and occurred at a depth of 25 km according to both the USGS and EMS. So far, 89 aftershocks have followed the M=6.9, with the largest being a M=5.4. Based on data from the USGS, severe shaking was recorded close to the epicenter. Despite this, the USGS PAGER system estimates that both economic losses and fatalities will remain low. So far, over 700 people have reported feeling the quake on the USGS website, though the region is home to millions of people.

This map shows the location of today’s M=6.9 earthquake, in relation to the seismic swarm, which began on Saturday (22 April) and was highlighted by a M=6.0 and M=5.5. In addition to these quakes, there was also a M=5.4 aftershock farther inland. All of these quakes suggest that the sequence is moving inland and getting deeper.

 

This earthquake occurred within an earthquake swarm that started on Saturday, which was highlighted by a M=6.0 Saturday evening. Up to this point, 54 M=3.0+ earthquakes have occurred offshore of Valparaiso in the last 2 days. To read more about the swarm, click here. Based on the initial depth reported by both the USGS and EMS, this quake likely occurred above the megathrust (subduction zone) on a secondary shallowly dipping splay.

This figure shows a time series of the earthquakes offshore of Valparaiso and Santiago Chile in the last 2 days. Two days ago, a seismic swarm began, and was highlighted by a M6.0 Saturday (22 April) night. Now, a M=6.9 has shook the region.

 

Chile is one of the most seismically active countries on earth, with the large majority of quakes occurring on or near the subduction zone. Based on the Global Earthquake Activity Rate (GEAR) model, which forecasts earthquake magnitudes globally using strain rates and seismicity since 1977, this earthquake should not be considered surprising, as the region is susceptible to M=7.5+ quakes. Nonetheless, this is a major quake and caused buildings to sway in the capital. We will post a more in-depth post on this quake later.

This Temblor map shows the Global Earthquake Activity Rate (GEAR) model, which forecasts the likely earthquake magnitude in your lifetime anywhere on earth. Based on this model, the M=6.9 earthquake which just occurred should not be considered surprising as the region is susceptible to M=7.5 earthquakes.

 

References
USGS
EMS Catalog