Earthquakes in Record and Earthquake Damage in the Past
1. Earthquakes in record (see the chart)
2. The characteristics of earthquake disasters .,
2-1 For there are three faults developed through the city proper, the earthquakes occurred were classified as right beneath the city type. And many cases, the macroseismic epicenters were close or overlapping. For instance, the M5.0 earthquake in 1954, the M4.6 earthquake in 1965 and the M5.0 earthquake in 1985 were all occurred beneath the downtown area with high-density population and building. The distances between three epicenters above were within 5 kilometers (Fig. 2). The overlapped VI degree area of three quakes was 8.62 square kilometers. The overlapped VII degree area of M5.0 quakes was 1.7 square kilometers. In many occasions, the earthquakes led to such secondary geological disasters as ground fissure and collapse, for example, a landslide caused by the M5.0 earthquake in 1985 blocked up the road (south entrances into city) for several hours.
2-2 Shallow hypocenters, low Magnitude, high Intensities, serious disaster damage
In Zigong, the sedimentary cover is only 6-7 kilometers thick and the focal depths are generally less than 10 kilometers. The landform of the city is valley-hill. These disadvantageous topographic and geological conditions led to various types of disaster damage and aggravate the damage. For instance, in M5.0 earthquake on March 29,1985, there were 278 people injured and 2 people died. The economic loss was 1.06 hundred million RMB.
2-3 Widespread quasi-resonate phenomena
Because the predominant periods of sandstone and chalkstone ground are approximate to those of most building in the city. It is apt to result in quasi-resonate phenomena and aggravate the damage.
Fig.2 Seismic Intensity Distribution in Zigong Area
Earthquakes above 4.0 during last 100 years and the disasters in ZiGong
| Date | M1. | Epicenter | Situation of Disasters | |||||||
| Northern Latitude | Eastern Longitude | Location | ||||||||
| 1896/2/14 |
|
2923 | 104.67 | YuanTan | Over 90 houses damaged, over 20 people died, 12 people injured | |||||
| 1905/11/9 | 5 | 29.4 | 104.7 | ZiGong | Several houses damaged, hill slipped. 13 people died | |||||
| 1927/5/22 |
|
29.4 | 104.7 | ZiGong | Strong feel, Houses collapsed | |||||
| 1947/10/17 |
|
29.4 | 104.8 | ZiGong | Strong feel, Houses collapsed | |||||
| 1954/10/24 | 5 | 29.4 | 104.8 | DongZiJing Da'an |
31people injured,
67houses collapsed, 1296 houses haven damaged. Economic loss 452,900yuan. Surface fractured, highway bed subsided, ground sunk. brick plume tilted and broke, level and density of salt water changed, output of natural gas decreased |
|||||
| 1959/11/13 | 5.0 | 29.4 | 105.0 | YongFeng FuShun | No historical recording | |||||
| 1965/3/31 | 4.0 | 29.3 | 104.7 | ZiGong | Widely felt, wall fractured, tile and brick fallen, 12people injured | |||||
| 1965/4/11 | 4.6 | 29.3 | 104.8 | DouYaWan ZiGong | 422 stovepipe damaged, 487 barrier damaged, 12people injured by fallen tile and brick | |||||
| 1967/7/29 | 4.0 | 29.6 | 104.4 | Northern RongXian | No historical recording | |||||
| 1972/11/6 | 4.0 | 29.22 | 104.48 | Goujia'Ao ZiGong |
Tile fallen, factories an mines affected | |||||
| 1985/3/29 | 5.0 | 29.22 | 104.49 | LiaoGaoShan Da'An | 279people injured, 2people died, Economic loss 1.06 hundred million Chinese yuan | |||||
Data source (Country report)
1. Name: He YULIN
2. Organization: Earthquake Engineer, Seismological Bureau of Sichuan Province
3. Course: 1998 Sm
4. Title: SEISMIC HAZARD AND COUNTERMEASURES IN ZIGONG CITY, CHINA
