The death toll has risen to 615 and more than 1,088,400 others have been affected by this 6.5-magnitude earthquake in Southwest China's Yunnan Province. Why has the Ludian Earthquake led to so many injuries and deaths? Experts with China and Yunnan Seismological Bureau explained its unique effect.

First of all, though Yunnan lies in an area where earthquakes are frequent, the 6.5-magnitude quake was the biggest in the past 2 millennia.

Unusually for an earthquake, the Ludian earthquake’s epicenter was only 12km (about 7.5 miles) deep, meaning it was a shallow earthquake and the shock was felt strongly by people on the ground. According to the records, the fastest speed of the seismic wave from east to west was 985 gal, which is why there were so many injuries and deaths. When a seismic wave reaches a speed of 1000 gal, everything on the ground will be flipped in the air, explained senior engineer Li Daogui with the Yunnan Seismological Bureau. 985 gal is already fast enough to cause serious injuries.

Another reason for the huge damage resulted from the high density of population in this area. Statistics shows there were 265 people per square kilometer, more than double the average for the province. Moreover, Ludian area is economically backward, and buildings were not solid enough to cope with a major earthquake - another major factor in the tragedy.

Ludian lies between several fracture zones, its complex geology, rugged terrain, and fragile ground layers regularly cause disasters like landslide, debris flows, and barrier lakes, especially during the rainy season.

Journalists arrived at Xinping Village early in the morning of August 6th. Xinping Village is typical of the areas that have suffered severely in the Earthquake. 21 people died - 13 of them crushed by collapsed houses. Journalists noted that most of the houses were built on slopes, and 95% of those houses were made of adobe and were completely destroyed by the earthquake. Older people in the village lived in even worse housing.

Even though Yunnan government has been runninng a project of Seismic Safety in rural areas from 2007, and was planing to help 1 million families rebuild their housing over a 5-year period, most people in Xinping Village still thought it was too expensive to rebuild houses even with the financial assistance from the government.