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Description: Graphics and Scientific Information regarding China Earthquakes, Historical China Earthquakes, China Earthquake of 1556, China Earthquake of 1975, Chinas Earthquake of 1976, China Earthquake of 2008.
On February 4, 1975, a strong earthquake struck the Chagou township of Haicheng City in the Liaoning Province of northeast China.
Haicheng (at 40.83N, 122.75E) is a densely populated, industrialized city of about 1 million. However, the affected region had a population of more than 3 million. Although the earthquake was extremely damaging to property and caused heavy economic losses. the death toll was relatively low as this event had been predicted and evacuation had been ordered.
The Haicheng earthquake was the first earthquake to be predicted with some degree of accuracy. The following is an overview of the parameters and of some of the extraordinary precursor phenomena that proceeded this event - which were widely observed or recorded, thus contributing to a successful prediction. A detailed report on this event has been compiled by the Earthquake Administration of the Liaoning Province. The following is a brief overview.
Fault Plane. Coseismal intensity lines, aftershock distribution and surveys of deformation patterns indicate that the main rupture plane of the earthquake involved a left-lateral strike slip with a NWW orientation (strike = 288°, dip = 78° N, rake = 342°) .
The total affected area was about 760 square Kms. The major axis of the affected area was elliptical and had N65°W orientation. The major axis of highest intensity (IX) was estimated to be 51km long and about 22km long. However, the region with lesser intensity (VII) was about 165km long and And the isoseismal curves also expanded towards NE direction, with 157km in length and 9,000k? in area. There were general surface cracks and spurted sand and water in plain land areas, but seldom in mountainous areas.
Felt Reports and Intensities: Ground motions from the Haicheng earthquake were extensively felt in the adjacent provinces of Suihua, Mudanjiang and Nenjiang, as well as in the Heilongjiang, Huaiyin, Suqian and Jiangsu provinces.
According to official reports 2,041 people were killed and 27,538 were injured. The number of fatalities was relatively low for an earthquake of this size in a densely populated area. It was estimated that the number of fatalities and injuries would have exceeded 150,000 if no earthquake prediction and evacuation had taken place. However, the earthquake was extremely damaging and caused heavy economic losses . 90% of the structures in Haicheng were severely affected. Homes, transport pipelines and more than 2,000 bridges were damaged.
Precursor Observations and Phenomena - There were numerous precursor events and unusual animal behavior that helped predict the occurrence of this earthquake. As early as 1970, the State Seismological Bureau had identified the Liaoning Province as an area of high seismic risk. According to the Earthquake Administration of Liaoning Province, beginning in September of 1973, there had been numerous anomalies in short term water levels, seismicity and radon gas content in groundwater, which developed in Jin County.
In June 1974, a little more than six months before the earthquake struck, there was a flurry of small earthquakes in the region . Based on this activity, a medium term prediction was made that a magnitude 5-6 earthquake might occur in the northern Pohai area in the next 1-2 years. Also, gravimeter surveys that had been carried out in the region earlier in 1972 and 1973 (Chen et al. 1976) , had revealed considerable variations in gravity values - however with no explanation of their significance.
In the next few months of 1974, there were numerous additional precursor phenomena and deformation in near heliozoan Peninsula area, such as changes in land elevation and in ground water levels. The regional increase in seismicity (which later was recognized as foreshocks) triggered a low-level alert. This activity occurred near the cities of Haicheng and Yingkou. The most important precursors were additional foreshock sequences.
On January 13, 1975, at a State Seismological Bureau conference, a shorter-term prediction was made that there would be an earthquake of about 5.5-6 magnitude in the Yingkou-Dairen - Tantung region of Liaoning Province in the first six months of the year. The predicted area included the cities of Yingkou (40.67N, 122.25E), Dairen (38.92N, 121.58E) and Tantung (40.17N, 124.34E), all somewhat south of Haicheng (40.83N, 122.75E) - which was not included.
Earthquake Warning Issued - Precursor earthquake activity in the Haicheng area intensified on February 3,1975. On February 4 - the day of the earthquake - based primarily on the observed unusual behavior of animals, a local county government authority issued a specific evacuation order for the immediate area. Subsequent actions that were taken, effectively constituted an imminent (and successful) prediction that an earthquake would strike. Based on these warnings that were issued about 5 1/2 hours prior to the event, a massive evacuation begun in the afternoon and early evening of February 4". However, the evacuation was extremely uneven across the region, as critical decisions to evacuate or not were made unilaterally by the local government authorities and by individual citizens acting spontaneously and independently. Nonetheless, these evacuation actions helped save thousands of lives. Also, the timing of the earthquake at 19:36 in the evening contributed to minimizing the overall death toll.
Following the disaster, there was some criticism about the effectiveness and validity of the short-term prediction. The short- term prediction - six months earlier - had left Haicheng as being out of risk on the basis that no earthquake had occurred before and there were no known seismic gaps in this area. Thus, when the earthquake finally occurred in Haicheng , it was a surprise.
Unusual Animal Behavior and Other Specific Precursor Phenomena - There were widespread reports of unusual animal behavior in the Haicheng region as early as mid-December of 1974. Near the end of December 1974, these observations were succeeded by a swarm of earthquakes. During the following month, January 1975, thousands of reports of unusual animal behavior were being received from the general area. In the days before the earthquake struck, the unusual animal behavior intensified. In the first three days in February the activity intensified even more. There were reports of unusual behavior involving larger animals, such as cows, horses, cats, dogs and pigs. An apparent increase in the ground temperature was also observed. The most unusual circumstance of animal behavior was that snakes came out of hibernation but subsequently died on the frozen ground. Also a group of rats appeared in the area.
Additional precursory phenomena were also observed and reported. For example, two hours before the earthquake struck, water fountains of up to 2.3 meters in height were observed, as well as an increase of pressure at an oil well. Reportedly, just a minute or more prior to the earthquake there were emissions of sulfurous gas. Also, just a few seconds prior to the earthquake, bright purplish red flashes were seen in the night sky at the Tang-Wang-Shan train station near Haicheng. Following this Haicheng earthquake, Chinese scientists began to study systematically the unusual animal behavior as a way of forecasting earthquakes.
Regardless of the significance of the Haicheng earthquake prediction in the long run, preparedness and public education were the key factors that kept the death toll relatively low. Government authorities were fairly well prepared. They had distributed educational brochures to the public about earthquakes and how to observe and report precursory phenomena so that predictions could be made.
As previously indicated, the coseismal intensity lines, the aftershock distribution and subsequent surveys of crustal displacement patterns indicate that the main rupture plane of this event involved a left-lateral strike slip with a NWW orientation (strike = 288°, dip = 78° N, rake = 342°) .
Subsequent studies of the seismic waves estimated the seismic moment to be at 3 x 1026 dyne-cm and the source duration 7 sec. Since the fault length of this earthquake was about 22 km, the observed P waves supported a rupture velocity of about 3.2 km/sec. The average dislocation was computed to be 2.8 m and the stress drop about 53 bars (Cipar, 1979) .
The seismicity of the entire region is the result of extension caused in part by the southeastward extrusion of Southeastern Asia. (Tapponnier and Molnar, 1977; Peltzer and Tapponnier, 1988) . However, large earthquakes in the North China region also appear to be associated with some mechanism of extension that results in shallow crustal mass transfer. Such shallow seismic activity in densely populated areas such as Haicheng or Tangshan can be extremely damaging.
The region where the 1975 Haicheng earthquake occurred is characterized by an active structural system, not only in Haicheng-Yingkou region but also along the entire South Liaoning Province . According to the Earthquake Administration of Liaoning Province, the seismic activity is mostly concentrated along a belt region bounded by the Liao River depression and the Liaodong Peninsula uplift. The activity of the tectonic structure is oriented in NW direction and has formed a series of active faults and new folds.
Active faults in the region with a NE orientation include the Niuju-Youyangou, the Jinshanling, the Shuangtaizihe-Zhaojiabaozi fault and the Jinzhou. Other faults in the area include the Dayanghe, the Ximuhe, the Zhuanghe and the Yalujiang.
The epicenter of the Haicheng earthquake was located in the region where faults with the NE and NW directions converge, but do not intersect (Earthquake Administration of Liaoning Province ) . Stress along the Dayanghe fault - which has a NW orientation - was apparently released by the Haicheng earthquake.
The North China basin where the February 4, 1975 Haicheng earthquake occurred, is a densely populated region and thus very vulnerable to earthquakes. According to historical records there have been 6 earthquakes of Ms 8 and 16 earthquakes of Ms 7 in this region during the past 2000 years (Gu, 1983; Ma, 1988) . These large earthquakes generally have occurred along major active faults that bound large basins.
Numerous strike-slip and normal faults are the predominant active structures in the region. Fault-plane solutions of these earthquakes usually show right-lateral strike-slips with a normal dip-slip component. Every earthquake of Ms 6 or more has the potential for causing serious loss of life and economic damage (Ma et al. 1989) .
Although earthquake recurrence intervals along any individual fault are relatively long (usually in the range of several thousand years), the composite recurrence interval for the whole region is in the order of a few decades ( Ma et al. 1989) . Five earthquakes with Ms > 7 occurred in this region between 1966 and 1976. These earthquakes resulted in hundreds of thousands of casualties and in significant economic damage. Worse of all was the 1976 Tangshan earthquake in the Hebei Province, a year after the Haicheng event.
Earthquake Administration of Liaoning Province Quan Yingdao, "An Earthquake of MS7.3 in Haicheng, Liaoning Province on February 4, 1975", World Data Center for Seismology, Beijing
Chen, Yun-Tai; Gu, Hao-Ding; Lu, Zao-Xun "Variations of gravity before and after the Haicheng earthquake, 1975, and the Tangshan earthquake, 1976", Physics of the Earth and Planetary Interiors, Volume 18, Issue 4, p. 330-338.
Cipar John 1979, "Source processes of the Haicheng, China earthquake from observations of P and S waves", Bulletin of the Seismological Society of America; December 1979; v. 69; no. 6; p. 1903-1916
K. Wang, Q.-F. Chen, S. Sun, and A. Wang, 2006, Predicting the 1975 Haicheng Earthquake, Bulletin of the Seismological Society of America, June 1, 2006; 96(3): 757 - 795.
Zhonghao Shou, 1999 "The Haicheng Earthquake and Its Prediction", Science and Utopya 65, page 34, November 1999" (in Turkish)
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