四川地震的数据简报与结构成因分析
编译/Toohearts
2008年5月12日，北京时间14点28分，格林尼治时间6点28分，北纬31.021度-东经103.367度，我国四川省境内发生里氏7.9级地震。美国国家地质调查局地震台网USGS的最新数据使我们能更加清晰的了解这次地震。
下载官方简报（英文版）：
ftp://hazards.cr.usgs.gov/maps/sigeqs/20080512/20080512.pdf
USGS 地震简报
来自美国地质调查局-国家地震信息中心的消息：2008年5月12日，当地时间14时28分，中国四川成都西偏北90公里，北京西南方1545公里处发生地震。震级和位置有待于更新资料和进一步分析。
震感报告
中国大部有感，台湾及泰国部分地区有感。
USGS全球网地震震感及破坏力感知图，截至格林尼治时间5月12日23时40分，中国境内共有 来自97个城市的569个节点报告有感。（下图）
地质分析
此次地震是由于四川盆地西北边缘的逆冲断层或东北部逆断层活动引起的。震中和震源所示与龙门山断层活动相一致。其应力作用是青藏高原地壳缓慢移动致使四川盆地以及中国东南部以下的地壳与青藏高原地壳相抵的结果。
从大陆尺度而言，印度板块与亚欧板块每年以50毫米的速度接近，形成应力，导致了亚洲中部及东部的大部分地震。这种板块聚集大部分被亚洲高原地区的提升所吸收，另一部分便以青藏高原以东地区的地壳运动表现出来，形成地震。
四川盆地西北边缘已有破坏性地震的历史， 1933年8月25日的里氏7.5级地震造成9300人死亡。
Earthquake Summary
The following is a release by the United States Geological Survey, National Earthquake Information Center: An earthquake occurred 90 km (55 miles) WNW of Chengdu, Sichuan, China and 1545 km (960 miles) SW of BEIJING, Beijing, China at 12:28 AM MDT, May 12, 2008 (2:28 PM local time in China). The magnitude and location may be revised when additional data and further analysis results are available.
Felt Reports
At least 8,500 people killed. Felt widely in China. Also felt in parts of Thailand and Taiwan.
Tectonic Summary
The Sichuan earthquake of May 12, 2008, occurred as the result of motion on a northeast striking reverse fault or thrust fault on the northwestern margin of the Sichuan Basin. The earthquake’s epicenter and focal-mechanism are consistent with it having occurred as the result of movement on the Longmenshan fault or a tectonically related fault. The earthquake reflects tectonic stresses resulting from the convergence of crustal material slowly moving from the high Tibetan Plateau, to the west, against strong crust underlying the Sichuan Basin and southeastern China.
On a continental scale, the seismicity of central and eastern Asia is a result of northward convergence of the India plate against the Eurasia plate with a velocity of about 50 mm/y. The convergence of the two plates is broadly accommodated by the uplift of the Asian highlands and by the motion of crustal material to the east away from the uplifted Tibetan Plateau.
The northwestern margin of the Sichuan Basin has previously experienced destructive earthquakes. The magnitude 7.5 earthquake of August 25, 1933, killed more than 9,300 people.
— Detials —
Magnitude 7.9
Date-Time
Monday, May 12, 2008 at 06:28:00 UTC
Monday, May 12, 2008 at 02:28:00 PM at epicenter
Time of Earthquake in other Time ZonesLocation 31.021°N, 103.367°E
Depth 10 km (6.2 miles) set by location program
Region EASTERN SICHUAN, CHINA
Distances 80 km (50 miles) WNW of Chengdu, Sichuan, China
140 km (90 miles) WSW of Mianyang, Sichuan, China
345 km (215 miles) WNW of Chongqing, Chongqing, China
1545 km (950 miles) SW of BEIJING, Beijing, China
Location Uncertainty
horizontal +/- 4.9 km (3.0 miles); depth fixed by location program
Parameters
NST=233, Nph=233, Dmin=592.2 km, Rmss=1.24 sec, Gp= 25°,M-type=moment magnitude (Mw), Version=A
Source USGS NEIC (WDCS-D)
Event ID us2008ryan
震中及震级分布图，震中所在地为北纬31.021度-东经103.367度，震源深度10公里。
