Econintersect: China experienced the second earthquake in two days as a shock between 6.6 and 7.0 on the Richter scale rocked the southwestern Chinese province of Szechuan (Sichuan). The mountainous province, in the eastern shadow of the Himalayas, experienced an even stronger earthquake in 2008 (7.9) which killed more than 87,000 people according to CNN. Early reports for the current quake have 180 fatalities and injuries for about 6,700. It may take many days to get final casualty counts because some of the affected areas are relatively remote with limited accessibility due to landslides disrupting transportation and communication.
Rescuers traverse landslide rubble to reach damaged villages. Click for larger image.
View rest of slide presentation at CNN.
Map from PlanetWare.com
On 18 April a 5.0 earthquake hit Yunnan province causing a few personal injuries and extensive property damage. This quake may or may not have been an aftershock of a 5.5 magnitude quake occurring on 03 March in the same location. Yunnan province is south of Szechuan and even closer to the Himalayan massif. In September 2012 two mid-5 quakes in Yunnan province resulted in 81 fatalities and more than 800 injuries.
Here is a summary of the Szechuan quake from CNN:
The quake struck just after 8 a.m. local time Saturday, about 115 kilometers (70 miles) away from the provincial capital, Chengdu, at a depth of around 12 kilometers, according to the U.S. Geological Survey. There was conflicting information about the earthquake’s strength, with the USGS putting the magnitude at 6.6 and the China Earthquake Networks Center gauging it at 7.0.
It was followed by a series of aftershocks, some of them as strong as magnitude 5.1, the USGS said.
The USGS listed 15 aftershocks aftershocks of magnitude 4.4 and greater, with four of them at 5.0 to 5.2. Data listed as of 14:16:53 UTC 21 April 2013 by the USGS (U.S. Geological Service).
The earthquake originated from tectonic plate movement involving the Tibetan Plateau overthrusting the lower land to the east along the Longmen Shan Fault. From Yahoo.com:
Tibetan Plateau and the Szechuan Basin lowlands. With each earthquake, a fault thrusts the plateau over the basin, shortening the distance between the two regions. The fault zone stretches more than 150 miles (240 km) along the base of the Longmen Shan Mountains. The mountain front is known for its amazingly steep rise — from 2,000 feet (600 meters) elevation in the basin to 21,325 feet (6,500 m) in the mountains, all in just 30 miles (50 km).
The earthquakes in Szechuan ultimately result from the collision between the Indian and Eurasian tectonic plates, according to the USGS. As India drives northward into Asia, it forces the Tibetan Plateau out of its way, eastward into China.
The geologic setting of the Szechuan Basin earthquake damage. As seismic waves travels across the basin’s deep pile of sediments, the waves slow down, spending more time shaking the area, according to a Caltech report prepared after the 2008 earthquake. Their strength also increases, compounding damage from shaking, the report said.
Sources:
- Strong quake hits southwestern China, killing at least 179 (Jethro Mullen and Steven Jiang, CNN, 20 April 2013)
- Earthquakes – 7 days, M2.5+ (USGS, 21 April 2013)
- What Caused The Deadly China Earthquake? (Becky Oskin, OurAmazingPlanet Staff Writer, LiveScience.com, Yahoo.com, 21 April 2013)
