M=5.0 Taiwan earthquake preceded by foreshock sequence

By David Jacobson, Temblor

See earthquakes in Taiwan

Southwestern Taiwan was hit by a M=5.0 earthquake today. This quake was preceded by a foreshock sequence that lasted approximately 33 hours. (Photo from: holidayssg.com)


At 9:10 p.m. local time today (24 May), a M=5.0 earthquake struck western Taiwan near the city of Chiayi, which is home to over 250,000 people. This earthquake was preceded by a foreshock sequence of five earthquakes beginning approximately 33 hours earlier. The foreshock sequence began with a M=3.6, and culminated with another M=3.6 five minutes before the M=5.0. Most earthquakes are not preceded by a foreshock sequence, making this quake rare. At this stage, there have been no reports of damage, and according to the Taiwan Central Weather Bureau, moderate shaking was felt in the M=5.0, which can rock buildings, and cause slight damage. So, close to the epicenter, it is possible that minor damage was sustained. Should we hear any reports of damage, we will update this post.

This Temblor map shows the location of the M=5.0 earthquake in Taiwan. In addition to the location from EMSC, the USGS location is also shown to illustrate the discrepancy in the catalogs. One of the earthquakes in the foreshock sequence is also shown.


At this stage, there is a discrepancy between where the USGS and EMSC plot the location of today’s quake. The USGS has it in a stepover between the Chiuchiungkeng and Muchiliao-Liuchia faults, while EMSC has it just to the east of the Chiuchiungkeng Fault. The USGS location has been added to the Temblor map above so that this discrepancy can be seen (For any location outside the United States, Temblor shows EMSC data). The USGS has also produced a focal mechanism for this earthquake, which suggests both strike-slip and extensional components of slip, which is not consistent with the regional geology. Should a Taiwan focal mechanism come out, we will update this post.

Based on the location shown in Temblor, this earthquake was likely associated with the Chiuchiungkeng Fault, a thrust fault within the southwestern foothills of Taiwan. Because of high slip rates associated with this fault, the region is believed to have a high probability of experiencing a large magnitude earthquake. This is verified when we look at the Taiwan Earthquake Model (see below). This model shows the likelihood of strong ground motion in the next 50 years.

This figure shows the Taiwan Earthquake Model with recent earthquakes shown. This colors in the figure represent ground motion values (g) with a 10% likelihood in 50 years. This is the spectral acceleration at a period of 0.3 seconds (3.3 Hz).


In addition to the Taiwan Earthquake Model, we can also consult the Global Earthquake Activity Rate (GEAR) model, to see what the likely earthquake magnitude is for this portion of Taiwan. This model, which uses global strain rates and seismicity since 1977, forecasts what the likely earthquake magnitude in your lifetime is for any location on earth. From the Temblor map below, one can see that a M=7.5 earthquake is likely in your lifetime. Such a quake could be devastating to the country, as a significant portion of the country’s agriculture is grown in southwestern Taiwan, and a large earthquake could damage valuable resources. Should anything change regarding the location or focal mechanism from today’s earthquake, we will update this post.

This Temblor map shows the Global Earthquake Activity Rate (GEAR) model for Taiwan. What can be seen from this figure is that the area around today’s earthquake is susceptible to M=7.5+ quakes. Such an earthquake would be devastating to the area.


European-Mediterranean Seismological Centre (EMSC)
Taiwan Earthquake Model (TEM)
Taiwan Central Weather Bureau