Some Seismological Notes on the May 12, 2008 Sichuan, China Earthquake

Steve Gao & Kelly Liusgao@mst.edu, liukh@mst.edu

Associate Professors of GeophysicsMissouri University of Science and Technology

Rolla, MO 65401http://www.mst.edu/~sgao

Focal parameters of the quake

• Magnitude 7.9 (based on USGS determination)• Time: May 12, 2008 at 14:28:00 local time• Location 31.021N, 103.367E• Focal depth 10 km• Location: 80 km WNW of Chengdu, 140 km WSW of Mianyang, 345 km WNW of

Chongqing, and 1545 km SW of Beijing• Instrumental Intensity at the epicenter: ~9• Instrumental Intensity at Chengdu: 6-7• Current (5/13 10:00 US Central Time) Death Toll: ~12,000

To view real-time earthquake activity, go to

http://www.iris.edu/seismon

The force that produced the earthquake was originated from the northward movement of India relative to Tibet.

http://picasaweb.google.com/mail2vijayreddy/WorldAtlas/photo#5176003781132706594

Many earthquakes in China were caused by the continental collision between India and Tibet

Scanned from “Lithospheric Dynamics Atlas of China”

China’s earthquake potential (redder = more dangerous)

http://www.air-worldwide.com/_public/NewsData/000994/China_Risk_Map.jpg

The May 12, 2008 earthquake (hand-drawn black star) occurred along the LongMenShan fault, which was responsible for magnitude ~6 quakes over the past ~400 years.A more active fault at the north of the May 12 quake in the SongPan area produced stronger quakes including the 7.2 in 1976 and 7.5 in 1933

Scanned from “Lithospheric Dynamics Atlas of China”

The LongMenShan fault is mostly a thrust fault produced by the eastward “escape” of the eastern Tibetan Plateau

http://www.cacegypt.org/Sinai/homework/GREG/pages/Q2_04/Fault_Types.html

Over the past 30 hours a total of about 40 magnitude >= 3.5 quakes have occurred. Most of the aftershocks are on the NE part of the mainshock.

The largest aftershock is a 6.0 occurred 15 minutes after the mainshock

Notes about earthquake prediction

• For a successful prediction, three critical parameters must be predicted:

• 1). Location (the error must be within a few hundred km)• 2). Time (error within a week or so)• 3). Magnitude (the error within one magnitude unit – a difference in

one magnitude unit corresponds to a 32-fold difference in energy release!)

• Potential for magnitude > 6.5 aftershocks is high• At the present time, no one on earth can predict earthquakes• Some claimed “precursors” such as strange behaviors of animals

are not consistently observed before most of the large quakes. The problem is the same for more scientific precursors such as ground tilt, water chemistry changes, changes in earth’s gravity and magnetic fields, and changes in atmospheric features (“earthquake clouds”)