a preliminary and urgent report on the m6.1 earthquake in sichuan-yunnan-guizhou rg, china

8/12/2019 A preliminary and urgent report on the M6.1 Earthquake in Sichuan-Yunnan-Guizhou RG, CHINA

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A preliminary and urgent report on the M6.1 Earthquake in

Sichuan-Yunnan-Guizhou RG, CHINA

Jamileh Vasheghani Farahani, Institute of Geophysics, University of Tehran, Tehran, Iran.

Abstract

Sichuan-Yunnan region is located in southwestern china. Major seismic events in this region

correspond to continental earthquakes. The region is a very active seismic zone in the world. Anearthquake in China is occurred in Sichuan-Yunnan-Guizhou RG, China with Mw=6.1 at

08:30:13 UTC on 3 Aug 2014 (EMSC). The epicenter of the earthquake determined by USGS,

27.245N 103.427E and its depth was 10.0km (6.2mi). Two days after this event is reported that

the Sichuan-Yunnan-Guizhou strong motion caused more than 450 people death and

approximately 2226 people injured. Moreover, 12,000 houses have collapsed and at least

100,000 damaged due to various extend. Intensity distribution is at least VIII intensity at the

epicenter. The fault caused 1996 Lijian earthquake is known in the further east of the epicenter.

The Focal Mechanism is a mainly horizontal movement, which is the most dangerous type of

earthquakes (shallow strike-slip faulting).

Key words: Sichuan-Yunnan area, earthquake, shallow strike-slip faulting, China.

Introduction

Sichuan and Yunnan in china are two active provinces and they have experienced some

earthquakes with M7. Sichuan-Yunnan region is located at the east edge of Qinghi-Xizang

(Tibet) Plateau. This area is the middle-southern section of North-South seismic zone in the

central part of Chinese mainland (Wei-bin and Guo-fang, 2004). A strong, shallow earthquake with

magnitude of 6.5 (CENC - China Earthquake Networks Center) strongly struck Ludian county of

Yunnan province, China, on August 3, 2014, at 08:30 UTC (16:30 local time). CENC is reported

a depth of 12 km. According to USGS, epicenter was located 11 km WNW of Wenping, 29 km

WSW of Zhaotong, 91 km WNW of Weining and 135 km (84 miles) ESE of Xichang, China.


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Table 1 shows the estimates of the hypocentral location of the earthquake by Harvard University,

USGS and CENC (China Earthquake Networks Center).

Hypocentral location

ReferenceDepth

(km)

MagnitudeLongitude E

(degrees)

Latitude N

(degrees)

Harvard14.46.2 (Mw)103.5227.07

USGS106.1 (Mw)103.4227.24

CENC(Fig1)126.5 (M)103.3027.10

Figure-1 show epicenter of earthquake using CENC report. Moreover, focal mechanism of the

event is shown on the map by reporting Harvard University and USGS.

Figure1- Epicentral region CENC (China Earthquake Networks Center).


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Seismotectonic Setting

A strong earthquake occured in northwest of Wenping, in Yunnan Province, China on Aug 3,

2014. This event was a result of shallow strike-slip faulting within the crust of the Eurasia plate.

Tectonics in the region are managed by the convergence of the India plate with Eurasia, which

has driven the uplift of the Himalayas to the west of Sichuan-Yunnan earthquake, 03 Aug 2014,

and has caused the formation of numerous intraplate continental transform structures in the

surrounding area, consisting the left-lateral Xiaojiang fault system.

In this area, local deformation rates show as much as 10 mm/yr of left-lateral shear movement

and in the latitude of the this event, India moves northwestward with respect to Eurasia at a rate

of approximately 51 mm/yr (USGS).

Focal Depth

The focal depth of the earthquake was reported to be 10 and 14.4 km respectively by the USGS

and Harvard University (http://www.usgs.gov and http://www.globalcmt.org/CMTsearch.html).

Therefore this is a shallow crustal earthquake.

Focal Mechanism

The focal mechanism of the 03 Aug 2014 earthquake determined by Harvard University. The

result related to the focal mechanism is listed in Table2.

Table 2

Focal mechanism Information of the Sichuan-Yunnan-Guizhou earthquake (Harvard University)

Strike Dip SlipStrike Dip Slip

MsMw

70 85 180160 90 56.16.2

Seismicity and important faults in the region

Sichuan-Yunnan area is very active in view point of tectonic and seismicity (Figure 2). Figure 2

shows seismicity in the region during 1900/01/01 to 2014/08/04. There are several active faults


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in this region: Xianshihe fault, the Red River fault, Xiaojiang fault and Jinshajiang fault

(Figure3, Meng and et al, 2008). Xianshihe fault, Anninghe-Zemuhe fault and Xiaojiang fault are

located in the east boundary Sichuan-Yunnan block. Jinshajiang fault and Honghe fault are in the

west boundary. The boundary of Sichuan-Qinghai block includs of Xianshuihe, Minjiang,

Longmenshan and East Kunlun faults. The Xianshuihe fault is the boundary between the two

blocks (Wei-bin and Guo-fang, 2004). They are active faults that strong earthquakes have produced.

There are strong earthquakes are typical in the Yunnan, and bordering Sichuan provinces, the

region with 500 km of the August 3 earthquake has hosted 27 other earthquakes of M6 over the

past century (USGS). Figure 4 shows strongest earthquakes in the region from 1900 within 150

km radius from this event (03 Aug 2014).

Figure 2- Seismicity in the region from 1900/01/01 to 2014/08/04.


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Figure 3- Distribution map of main active faults in Sichuan-Yunnan area.

The most important aftershock occurred in the region with magnitude 4.7 on 3 Aug 2014

(EMSC) and depth=10km (Local time: 21:47:11, GMT/UTC Time : 2014-08-03 13:47:11).

In Table3 significant earthquakes in the region are listed with magnitudes 6.5(USGS).


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Table 3- Earthquakes with magnitudes 6.5 (USGS) in the region.

Figure 4- Strongest earthquake in the region from 1900 to 2014.


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Intensity and Structure Information Summary

Earthquakes in Yunnan, and bordering Sichuan provinces are fatal and then residential structuresin this area have high vulnerability. Earthquakes with magnitudes range, M=5-6 in April 1985,

October 1995, November 2003, August 2004 and 2006 caused a lot of fatalities. In one of the

strongest events (October 1995, Mw= 6.2) around 50 people were killed. Unfortunately, event in

03 Aug 2014 had many casualties. Seismic hazard map Produced by USGS. Figure5 shows

seismic hazard map that it is stated as peak ground acceleration (PGA) on firm rock, in

meters/sec2. It beilived to be exceeded in a 50-yr period with a probability of 10 percent.

Figure 5- Seismic harzad map (USGS).


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Figure 8(a) taken by cell phone and released by China's Xinhua News Agency, men at rubbles of

buildings look for survivors earthquake in Ludian County of Zhaotong City in southwest China's

Yunnan Province Sunday, Aug. 3, 2014. Chinese state media reported that this event was felt

most strongly in Yunnan as well as in the neighboring of Guzhou and Sichuan. Moreover, the

official Xinhua news agency reported the epicenter was in Longtoushan town in Yunnans

mountainous Ludian county. The earthquake caused, many people rush out of buildings on to the

street after the event hit. Also, electricity supplies were cut and at least one school collapsed,

Xinhua added, with more than 12,000 houses having collapsed and 30,000 sustaining damage

(http://www.vosizneias.com).

Figure7- Shake map of SICHUANYUNNANGUIZHOUearthquakeinChina(USGS).


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(a)

(b)

Figure 8(a) and (b)- Vulnerable building types in the region (Source:


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http://www.ydr.com/portlet/article/html/render_gallery.jsp?articleId=26267858&siteId=515&sta

rtImage=3).

Some other details about economic losses, estimated fatalities and other detailed information are

providedbyUSGS.Wehaveshownthisinformationintheappendixpart.

Conclusion

A preliminary and urgent analysis indicates the following results for the strong earthquake in

China: An earthquake (Mw=6.1) struck southwestern china on August 3, 2014, at 08:30 UTC

(16:30 local time). According to USGS, epicenter was located 11 km WNW of Wenping, 29 km

WSW of Zhaotong, 91 km WNW of Weining and 135 km ESE of Xichang, China. The

earthquake approximately killed more than 450 people, injured 2226 and about 12,000 mostly in

the collapsed brick houses. The area is seismically active and in 2008, an earthquake in Sichuan

killed almost 70,000 people. The maximum intensity was estimated to be VIII+on the Modified

Mercalli Intensity Scale at the epicenter. The focal mechanism and the focal depth of the

Sichuan-Yunnan-Guizhou earthquake is determined by the USGS and Harvard University. It was

shallow strike-slip faulting. The focal depth of the earthquake indicates a shallow crustal event.

This report was prepared 2 days after the earthquake as a preliminary and urgent overview the

earthquake occurrence.

References

1. http://www.emsc-csem.org.

2. http://www.usgs.gov.

3. http://earthquake-report.com/2014/08/03.

4.

Wei-bin, H. and Guo-fang, J, 2004. Study on distribution characteristics of strong

earthquakes in Sichuan-Yunnan area and their geological tectonic background. ACTA

SEISMOLOGICA SINICA, 17(2), 230-243.

5. http://www.csndmc.ac.cn.

6. http://www.globalcmt.org/CMTsearch.html.

7. Meng, G., Ren, J., Shen, Z., Wang, M., Gan, W., Wang, Q. and Qiao, X, 2008. Research

in to fault motion in Sichuan-Yunnan region, China incorporating earthquake risk


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analysis. The 14th World Conference on Earthquake Engineering October 12-17, 2008,

Beijing, China.

8.

http://www.vosizneias.com/174048/2014/08/03/beijing-at-least-150-dead-after-quake-

hits-southwest-china.

9. http://www.ydr.com/portlet/article/html/render_gallery.jsp?articleId=26267858&siteId=5

15&startImage=3).


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Appendix:PAGER - M 6.1 - SICHUAN-YUNNAN-GUIZHOU REGION,

CHINA

a preliminary and urgent report on the m6.1 earthquake in sichuan-yunnan-guizhou rg, china

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