Earth Observatory Blog
M 5.6 Earthquake Strikes Northeastern Taiwan
A magnitude-5.6 earthquake occurred offshore Ilan in northeastern Taiwan on 12 May 2016. According to the United States Geological Survey, this is the second significant quake to have struck Taiwan this year.
Approximately an hour after the M 5.6 mainshock took place, a M 5.5 aftershock occurred east of the mainshock’s point of origin. This series of earthquakes is commonly referred to as a “doublet,” where two quakes of similar magnitudes occur in succession within a relatively short period of time.
The real-time fault-plane solutions1 show that both of these earthquakes were a result of normal faulting.2 Even though it was reported that tremors could be felt as far as northern Taiwan, including Taipei, the degree of ground motion in Taipei was moderate and therefore the resulting damage to properties in the city is unlikely to be extensive.
This expansion component is reminiscent of the aforementioned March 2005 earthquakes that had occurred to the west of the epicentre of today’s earthquake. The seismic distribution and ground motion of the 2005 earthquakes imply an association with dike, or fluid intrusions, associated with volcanic activity in which magma, or the fluid from magma migrating from the deep crust to the shallow earth, and triggered the earthquake activity.
The May 2016 event is possibly the result of the same volcanic-related process. Such volcanic-related phenomenon is not rare in Ilan area. The Turtle Island which, similar to a large sea turtle swimming along the Ilan’s coastline, is an active volcano island with a relatively “young” eruption record (< 6000 yrs). The Qingshui geothermal field, along the southern edge of the Ilan basin, may also be related to the igneous heat source. Further analysis of these earthquake sequences will help us to better understand the source of these earthquakes, and the tectonic kinematics behind them.
Further reading: Taiwan Earthquake Research Center
Thumbnail image from US Geological Survey
2Normal faulting is a process by which two blocks of rock are pulled apart by tension forces. The rock above the fault plane moves downwards relative to the rock mass beneath the fault plane.