THE ML 64 TAIWAN EARTHQUAKE OF MARCH 04 2010

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The ML 6

The ML 6.4 Taiwan Earthquake of March 04, 2010


Juin-Fu Chai, Che-Min Lin, Keng-Chang Kuo, Fan-Ru Lin, Yu-Wen Chang, Yao-Sheng Yang, Ker-Chun Lin and Chu-Chieh Jay Lin (M. EERI)

National Center for Research on Earthquake Engineering (NCREE)


Overview

On March 4, 2010 at 8:18:53.0 CST (00:18:53.0 UTC), a ML 6.4 earthquake took place in the mountain area of Kaohsiung in southern Taiwan. According to the Central Weather Bureau (CWB), the epicenter of the main shock was located at 23.00°N and 120.73°E, about 17.0 km SE of Jiashian Township. The revised focal depth was estimated at 22.6 km, but the original posted depth was just 5 km in the first report of CWB. The moment magnitude MW is 6.4 (USGS). The earthquake was felt all over the Taiwan Island (Fig. 1). The ground shaking level recorded at the nearest station was CWB Intensity V. However, the maximum ground acceleration was up to 0.31g (Intensity VI) recorded at CHN1 station located 29 km NW of the epicenter. There were over three-hundred aftershocks detected in two days after the earthquake. And twenty-five sensible aftershocks with ML greater then 3.0 occurred around the main shock in the five days. The largest magnitude of the aftershocks was ML 5.7. The most aftershocks were located alone WNW-ESE direction.

The earthquake occurred between the Western Foothill and the Central Mountain areas of Taiwan. The Western Foothill is a foreland fold-thrust belt on Eurasian Plate because of the collision of the Philippine Sea Plate and the Eurasian Plate. Although the Western Foothill is one of the major seismic belts of Taiwan, the seismicity of the area around the epicenter is relatively low. The largest historic earthquake was the 1964 ML 6.3 Paiho Earthquake occurred at about 15 km NNW of this time. The Chaochou Fault classed as an active fault of the second category by the Central Geology Survey (CGS) is close to the epicenter, but the depth and focal mechanism of the earthquake don’t agree with the Chaochou Fault. The fault plane solution indicates a thrust fault with NW-SE strike and NE dipping. An unknown fault or a transfer fault zone was supposed to explain the occurrence of the earthquake.


THE ML 64 TAIWAN EARTHQUAKE OF MARCH 04 2010

Fig.1: PGA map of the 2010/03/04 ML 6.4 earthquake in Taiwan


Damages on Buildings

The disaster caused by the earthquake was concentrated on the residential and school buildings. The damaged buildings mostly suffered cracks on walls or columns. There were two buildings collapsed in the disaster area. One is a three-story RC building with first story used as parking, and this building collapsed during the main shock because of the soft-story effect (see Fig. 2). Figure 3 shows the other collapsed building, which is also a three-story RC building and collapsed during the aftershock (ML 5.7).

For school buildings, the typical diagonal shear cracks on columns along the direction of the corridor can be found due to the short column effect. Figure 4 shows the typical column failure in shear mode for school buildings in disaster area. On the other hand, the hallway of the entrance in a school resulted in a soft-story system, and hence some damages can be observed there. The typical damage on the columns of hallway in a school building is shown in Fig. 5.


THE ML 64 TAIWAN EARTHQUAKE OF MARCH 04 2010 THE ML 64 TAIWAN EARTHQUAKE OF MARCH 04 2010 THE ML 64 TAIWAN EARTHQUAKE OF MARCH 04 2010

Fig.2: A three-story RC building collapsed caused by soft story effect


THE ML 64 TAIWAN EARTHQUAKE OF MARCH 04 2010 THE ML 64 TAIWAN EARTHQUAKE OF MARCH 04 2010 THE ML 64 TAIWAN EARTHQUAKE OF MARCH 04 2010

Fig.3: A three-story RC building collapsed during the aftershock (ML 5.7)


THE ML 64 TAIWAN EARTHQUAKE OF MARCH 04 2010 THE ML 64 TAIWAN EARTHQUAKE OF MARCH 04 2010

Fig.4: Typical shear cracks on the columns along the direction of the corridor were due to the short column effect


THE ML 64 TAIWAN EARTHQUAKE OF MARCH 04 2010 THE ML 64 TAIWAN EARTHQUAKE OF MARCH 04 2010

Fig.5: Damages on the columns of hallway in a school building



Damages on Nonstructural Components

Damage survey on nonstructural components was conducted on eight hospitals, ten schools and two college libraries located in the area where the PGA reached 80gal (seismic intensity V by the Central Weather Bureau, Taiwan ). The buildings of these facilities remained structurally intact or sustained only minor damage. The common nonstructural damage for these three types of facilities was suspended ceilings, which were observed in three hospitals, seven schools and one college library. The major damage to suspended ceilings occurred around the perimeter adjacent to structures, where runners deformed and detached from moldings and ceiling panels fell off. In addition, out-plane deformation occurred in several parts of the ceiling system. In four schools, the suspended ceilings in auditoriums suffered the aforementioned damage (Fig. 6). As auditoriums have a high and large span space, the restoration and repair of the ceilings will be complicated.

Damage to piping systems and elevators was the other prevalent nonstructural damage. Four hospitals sustained broken pipelines and two of them were severely flooded due to broken sprinklers (Figs. 7-8). The elevators were unserviceable in two hospitals due to short circuit of control panels. The most emergent response to nonstructural damage was reported in a school. The school was forced to suspend classes in the afternoon on that day because of poisonous gas leaked from overturned tables in a laboratory.


THE ML 64 TAIWAN EARTHQUAKE OF MARCH 04 2010

THE ML 64 TAIWAN EARTHQUAKE OF MARCH 04 2010

Fig. 6: Damaged suspended ceilings in the auditorium of a junior high school.

THE ML 64 TAIWAN EARTHQUAKE OF MARCH 04 2010

THE ML 64 TAIWAN EARTHQUAKE OF MARCH 04 2010

Fig. 7: Damaged suspended ceilings and flooding caused by broken sprinklers in a hospital.

Fig. 8: Flooding caused by broken sprinklers in a hospital




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