The cause of Wenchuan earthquake in Sichuan province

The Wenchuan earthquake was caused by the rapid uplift of the Qinghai-Tibet Plateau caused by the subduction of the Indian plate to the Asian plate. The focal depth is 10 km-20 km, which lasts for a long time and is extremely destructive.

First, the Indian plate subducted into the Asian plate, which led to the rapid uplift of the Qinghai-Tibet Plateau. The plateau material slowly flows eastward and squeezes eastward along the Longmenshan structural belt on the eastern edge of the plateau, encountering the tenacious resistance of the rigid block under the Sichuan Basin, resulting in the long-term accumulation of tectonic stress energy, and finally suddenly released in Beichuan-Yingxiu area of Longmenshan.

Second, thrust, dextral and compressional fault earthquakes. The seismogenic structure is the central fault zone of Longmenshan structural belt, which thrusts from southwest to northeast under the action of compressive stress. The earthquake was a one-way rupture earthquake, which moved from southwest to northeast, causing aftershocks to expand to northeast. After the main earthquake, the process of stress propagation and release is slow, which may lead to strong aftershocks and long duration.

The third is shallow earthquakes. Wenchuan earthquake does not belong to the deep plate boundary effect, but occurred in the brittle-ductile transition zone of the crust with a focal depth of 10 km-20 km, which is extremely destructive.

Blizzard and abnormal climate have two reasons.

The first reason is that we are in a La Nina state this year, that is, the SST in the equatorial eastern Pacific is below minus 0.5 degrees lower than normal, which has a very obvious impact on China's climate. Under the influence of La Nina phenomenon, the meridional circulation in East Asia is abnormal, which is very beneficial to the southward movement of cold air in northern China. It has given us a cold winter, so we can see that this cold winter has already appeared this year.

The second reason is that the two conditions that must be met when it snows or rains are 1. It comes from the warm and humid air flow in the tropics. There is cold air from high mountain area. The snowfall area in winter (the same as the rainfall area in summer) is distributed near the front, that is, the intersection of cold and warm air masses. This position is not fixed, but is determined by the strength of the two air masses. The cold air mass is weak, the front and precipitation areas have high latitudes, the cold air mass is strong, and the front and precipitation areas have low latitudes. The land cold high that affects China in winter is the Asian high centered on Mongolia and Siberia (also known as the Mongolian Siberian high), which has a very large sphere of influence and has a great impact on the weather in China, especially in the northern region. The cold air affecting our country in the early winter of this year is relatively weak, and the frequency is not much. Even with warm and humid airflow, it is not easy to snow without cold air. However, since 2008, the high pressure in Asia has been very active, and cold air masses have formed southward, affecting China and causing large-scale gale and cooling weather. However, due to the active warm air mass in the south this year, a large number of warm and humid air currents from the Pacific Ocean and the Indian Ocean frequently patronize the southern region. When the powerful cold air mass from Mongolia and Siberia quickly moved south to meet the warm and humid air mass, the cold and warm air just merged into one. Affected by these two air currents, there have been more rainy and snowy weather recently, especially in the Yangtze River basin, and the low temperature weather has lasted for a long time. If there is only a strong cold air mass without a large amount of water vapor provided by warm and humid air mass, there will only be strong winds and cool weather in the south; If there is only a large amount of water vapor provided by warm and humid air masses, there will be no disastrous weather at all without the arrival of cold air masses. When both are ready, disaster comes.