Mw 6.4 Earthquake Strikes Southern Taiwan

Mw 6.4 Earthquake Strikes Southern Taiwan

  • EOS News
07 Feb 2016

In the early morning of Febuary 6, 2016, a moderate earthquake struck Tainan, southern Taiwan, right before the Chinese New Year holidays. The quake damaged several buildings in the city, one of the oldest settlements at Taiwan. The magnitude-6.4 earthquake has a focal depth of about 20 kilometres (km) beneath the surface; the energy released by this earthquake is estimated to be four times greater than that of the Sabah earthquake in June 2015.

This earthquake caused many residential and office buildings to collapse and others to tilt, resulting in more than 70 casualties. The Taiwan High Speed Rail was also damaged by the temblor, forcing its operator to call off the high-speed train service until the damage could be repaired. The cancellation of the high-speed rail service hampered travel plans for thousands of Taiwanese planning to travel back to their hometowns for the Chinese New Year break.

Based on the focal mechanism solution, telesesmic waveform inversion, and the ground motion distribution of the mainshock, EOS scientists believe that the Tainan earthquake occurred as a result of the rupture of a blind shallow dipping fault beneath the foothills of southern Taiwan, with a complicated second rupture. The recent event shares many similar characteristics to the Mw 6.3 Jiasian earthquake in March 2010, which occurred approximately 10 km east of the present mainshock. Both of these events seem to be generated by the structures differ from the faults mapped on the surface, underneath the orogenic system.

Although the epicentre of the Tainan earthquake is in the foothills, the city suffered considerable damage from this earthquake because it is built on soft sediment layers that were deposited several thousand years ago. When the seismic wave propagated from the hard rocks to the soft sediments, its amplitude is magnified, resulting in stronger shaking in the plains. This seismic site effect may be the cause of damaged buildings in southern Taiwan. Scientists in Taiwan are now collecting more data on this earthquake to understand its real cause.

More aftershocks are expected in the next few days near the Tainan area. Within just three hours from the mainshock, more than 10 aftershocks occurred near Tainan, with magnitudes ranging between 3.7 and 4.9. While these aftershocks are not likely to cause more damages than the mainshock, there is a small chance that the Tainan earthquake could trigger another fault rupture nearby, causing another major earthquake in this region.

We are not expecting any tsunami resulting from this earthquake, located away from the Manila Trench, as the ground motion offshore is not strong enough to trigger the submarine landslide. However, a tsunami warning is likely to be given to the southern Taiwan if a strong earthquake event occurred offshore Southern Taiwan, much like the 2006 Hengchun earthquake that resulted in a submarine landslide that broke several submarine communications cables.

Cover image credit: US Geological Survey

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