LESSONS LEARNED FROM TAIWAN M 6.4 QUAKE

Buildings collapse in coastal Taiwan M=6.4 quake

POSTED ON FEBRUARY 6, 2018 BY TEMBLOR

By David Jacobson, Temblor

Check your hazard rank

VIDEO (00:01:24) - How will 3 buildings, engineered equally but built
on different types of ground, react to an #earthquake?" https://youtu.be/536xSZ_XkSs 

This picture shows the 270 Marshal Hotel, whose lower floors collapsed in today’s M=6.4 earthquake. (Photo from: KULAS_TW) 

A second large earthquake in 2 days strikes Eastern Taiwan

Just before midnight local time, a M=6.4 earthquake struck Eastern Taiwan, toppling buildings, collapsing ground floors, and buckling streets. The quake, which comes just two days after a M=6.1 approximately 20 km to the southeast, occurred at a depth of 10 km and registered very strong shaking in the city of Hualien according to the Taiwan Central Weather Bureau. Hualien is home to over 100,000 people. Yesterday, when we wrote about the M=6.1 over the weekend, we pointed out that its location marks the intersection of the Longitudinal Valley Fault and the Ryukyu Trench. Because of this, the area is prone to experiencing large magnitude earthquakes, meaning this quake should not be considered surprising. Further, earthquakes at fault junctions and tips are slightly more likely to trigger still larger shocks than others.

This Google Earth image shows the location of today’s M=6.4 earthquake near the city of Hualien, which is home to over 100,000 people. 

Significant damage within Hualien

This picture shows a partially-collapsed building in the city of Hualien, on Taiwan’s eastern coast. The earthquake which caused this damage was a M=6.4 quake which struck just two days after a M=6.1 just 15 km to the southeast. 

This picture from The Guardian shows a building which suffered at least a first story collapse in today’s M=6.4 earthquake north of Taiwan’s city of Hualien. 

Based on early reports and pictures, there is significant damage in Hualien, at least two people are confirmed to have been killed, and over 200 people were injured, 27 of them seriously according to the New York Times. Additionally, NPR announced that seven buildings had collapsed and while people remain trapped beneath the collapsed buildings, the National Fire Agency announced that they had rescued 149 people trapped in the rubble. However, people remain trapped in a partially-collapsed hotel. The photos above show some of the major damage sustained in the earthquake.

The reported damage is higher than forecast by the USGS PAGER system, which anticipated less than $1 million in damage. This is likely due to an underestimation of the amount of shaking around Hualien. The ShakeMap produced by Taiwan’s Central Weather Bureau can be seen below.

This figure shows the ShakeMap produced by Taiwan’s Central Weather Bureau. In the city of Hualien, shaking reached Intensity Level 7. 

A yet-larger earthquake could still occur

This Temblor map shows the location of the recent earthquake on Taiwan’s eastern coast. Both of the recent M=6+ quakes occurred at the northern tip of the Longitudinal Valley Fault, Taiwan’s longest and most active fault. 

While the earthquake over the weekend was predominantly compressional in nature, today’s event was nearly pure strike-slip, according to both the USGS and GFZ-Potsdam. Because of this, today’s quake may have struck at the northern tip of the Longitudinal Valley Fault, which is known to have both compressional and left-lateral motion. As we said yesterday, 30% of all earthquakes in Taiwan occur on or near this fault. It also has the highest slip rate of all faults in Taiwan.

  Domino Theory?

While the M=6.4 shock occurred offshore at the northern tip of the Longitudinal Valley Fault, several of its large aftershocks occurred 20 km (12 miles) to the south, beneath Hualien, also on or near the Longitudinal Valley Fault. So, there appears to be a seismic propagation of aftershocks along the Longitudinal Valley Fault. This raises concerns that these events themselves could be foreshocks to still larger earthquakes that could rupture south along Taiwan’s longest, and most active fault.

Today’s shock should not come as a surprise. The Taiwan Earthquake Model, a university, government, and industry consortium that uses the tools and libraries of the Global Earthquake Model (GEM Foundation), is shown below. The area around the recent earthquakes has one of the highest hazards in the entire country. Therefore, residents of Eastern Taiwan should be prepared for potentially larger, more damaging earthquakes, perhaps propagating to the south.

This figure shows the Taiwan Earthquake Model. What is evident in this figure is that the location of today’s earthquake is in a location of extremely high hazard. (Figure from Cheng et al) 

The video above shows damage sustained in today’s M=6.4 earthquake near the city of Hualien 

References
Taiwan’s Central Weather Bureau
EMSC
Taiwan Earthquake Model from, Thomas (Chin-Tung) Cheng et al., Disaster Prevention Technology Research Center, Sinotech Engineering Consultants, Inc. – Link
Kate Huihsuan Chen, Shinji Toda, and Ruey-Juin Rau, A leaping, triggered sequence along a segmented fault: The 1951 ML 7.3 Hualien-Taitung earthquake sequence in eastern Taiwan, JOURNAL OF GEOPHYSICAL RESEARCH, VOL. 113, B02304, doi:10.1029/2007JB005048, 2008
USGS
BBC
New York Times
The Guardian
NPR
http://temblor.net/earthquake-insights/buildings-collapse-in-coastal-taiwan-m6-4-quake-6227/?t=1&cn=ZmxleGlibGVfcmVjcw%3D%3D&refsrc=email&iid=72d888af3f08412cad0530700e82b464&fl=4&uid=765318905522946048&nid=244+281088008

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