Earthquake and Tsunami of July 18, 1969 in the Bohai Sea,
George Pararas Carayannis
On July 18, 1969 a major earthquake occurred in the middle of Bohai Sea. The North China basin where the 1969 Bohai Sea earthquake occurred, is a densely populated region - thus very vulnerable to earthquakes.A relatively small tsunami was generated. No details about the tsunami are available.
Date and Time of Origin: July 18, 1969
Epicenter: 38.2 N, 119.4 E> (see diagram on historic earthquakes).
Magnitude: M 7.4 on Richter Scale
Focal Depth: Shallow km.
Afteshocks: Numerous large aftershocks in the hours and days after the main earthquake.
Main Earthquake of July 18, 1969 and major aftershocks in the Bohai Sea.
Srike f=195°; Dip angle d=85 degrees; Slip angle l=65 degrees ; Seismic Moment M o=0.9x10 raised to the 19th power Nm; Rupture Length L=59.9km; Rupture propagation speed Vr=3.5km/s; Angle from the strike to the propagation direction L R =160 (Wu & Zang, 1989, 1992).
Seismotectonic Setting of the Bohai Sea Basin
The collision of India with the Asian mainland during the earliest Eocene (~50 Ma) has resulted in the growth of the world's largest orogenic belt, the Himalayas and the associated Tibetan plateau. The seimotectonic evolution of China is characterized by the merger of several microcontinents throughout the entire Phanerozoic (Zhang et al., 1984; Hendrix and Davis, 2001). The collision and the associated convergence and extension have created 64 major tectonic zones in China, which can be subdivided into a smaller number of tectonic "regions" (Zhang et al.,1984; Yin and Nie,1996).
The Bohai Sea is part of an inner-land sea basin that was formed during the Late Quaternary to the east of the Cenozoic rift basin of North China and it is a part of the Mongolian accretionary fold belt - an apparent collage of island arcs and possible microcontinental blocks (Davis et al., 2001). Both India-Eurasian tectonic collision and Pacific plate subduction may be responsible for the structural changes in the Bohai Basin and the formation of several dense seismic zones. The seismotectonic setting of this region is complex. The regional principal compressive stress - with an apparent NEE-SWW orientation - has formed a series of NE-trending active tectonic zones which form a group of conjugated shear fracturing systems. The Zhangjiakou-Bohai Sea is the seismotectonic zone controlling the present-day strong earthquake activities in the northern part of the North China region.
Other major active tectonic zones in the region are the northern section of the Northeast trending Yingkou-Weifang and Miaoxibei-Huanghekou-Linyi fault zones, and the Northwest striking Beijing-Penglai fault zone, which intersect at the center of the Bohai Sea basin. These tectonic zones subdivide the sea area into four secondary neotectonic areas, which are subject to a dominant horizontal, or nearly horizontal, compressive stress field in the direction NE60°–90, while the tensional stress in a NS-NW30° direction (Chen et al., 2007).
Most of the recent small earthquakes in the Bohai Basin had ruptures with prominent NE orientation, although there is also a seismic dense zone that has NW direction. The long-term crustal deformation pattern determined from GPS measurements exhibits a relatively complete left-lateral strike-slip movement along the active fault zone. However, studies on crustal deformation by stages (Chen et al., 2007) indicate that a series of NE-trending large-scale anomalous gradient zones have appeared along the Zhangjiakou -Bohai Sea fault zone.
Seismicity of the Bohai Sea Basin Region
The seismicity of the basin is stronger south of the 39°N parallel - and this is the area where most of the larger earthquakes have occurred. Almost all of the strong earthquakes and the dense seismic zones are concentrated in the southern part of the Bohai Sea. According to historical records there have been 6 earthquakes of Ms 8 and 16 earthquakes of Ms 7 in the area, in the past 2000 years (Gu, 1983; Ma, 1988). These large earthquakes generally have occurred along major active faults that bound the Bohai basin. Numerous strike-slip and normal faults on land in the Liaoning and Hebei Provinces are the predominant active structures where destructive earthquakes occurred in recent times. As previously indicated, the fault-plane solutions of earthquakes in the area usually show right-lateral strike-slips with prominent NE orientation, although some had NW orientation with a normal dip-slip component.
Historical Earthquakes in the Bohai Sea and Adjacent Regions
There have been several major earthquakes in the Bohai Sea region prior to the 18 July 1969 Bohai earthquake.
1548, September 22 - Estimated magnitude M 7.0 and epicenter at about 121.0 E.
1597, October 6 - Estimated magnitude M 7.0 and epicenter at about 38.5 N. 120.0 E. The strength of this event in the Bohai Sea was doubted (Wang, 2007).
1888, June 13 - Estimated magnitude M 7.5 and epicenter at about 38.5 N, 119.0 E. (Wu and Zang, 1989).
Historical earthquakes in the Bohai Sea and in Northeast China.
Recent major earthquakes with mostly land impact in the region include:
1975, February 4 - TheHaicheng earthquake of February 4, 1975 has magnitude M 7.3 had epicenter at 40.6 N, 122.8 E.
1976 July 28 - The main Tangshan earthquake had magnitude of M 7.8 and epicenter at 39.4 N. 118.0 E., The major aftershock on the same day had magnitude M 7.1 and epicenter at 39.7 N., 118.5 E.
Earthquake Recurrence Frequency
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.
The Tsunami of July 18, 1969
The earthquake of July 18, 1969 in the middle of the Bohai Sea, reportedly generated a tsunami with a height above normal tide level ranging from 1~2 m. No details are available as to the height of the tide at the time of the earthquake and whether the 1 to 2 meter tsunami that was reported occurred at high or low tide. The tsunami was responsible for losses in the coastal region near Tangshan, in the Hebei province, but no details are available.
Potential for Tunami Generation in the Bohai Sea
The half-enclosed Bohai Sea surrounds one of China's most populous and highest economic value regions. Along the shores of the Bohai Sea and along the Yangtze and the Pearl River Deltas, there are the most developed regions of Shandong, Hebei, Liaoning and Tianjin. Thus, marine disasters, such as tsunamis or hurricane surges, can have a significant impact on China's coastal populations and economy. Recetn earthquakes on land have had great impact. Tunamis do not pose as much of a threat, but locally destructive tsunamis could be generated in the future.
As indicated, earthquakes in the Bohai Sea involve primarily crustal movements with right-lateral strike-slips. Such earthquakes do not generate large tsunamis. However, strong motions from such events could trigger submarine landslides that could contribute to destructive local tsunamis.
Major rivers deposit large loads of sediments in the the Bohai and Yellow Seas and have created unstable slopes on the shelf that could become potential sources of landlside generated tsunamis.
Submarine Landslides - The Bohai Sea is a shallow marginal sea fed by sediments carried by major rivers such as Huang He, Luan He, Liao and alu Jiang. The mean depth of the Bohai is about 20 m, with the deepest region of about 70 m located near the northern coast of the Bohai Strait.
Geological structure plays an important role in the development of the palaeochannels in the North China Plain and in the offshore areas. Mountain uplift, subsidence of the plain, and tectonic movement of the basement since the Cenozoic, have interacted with the flashy fluvial regime involving high sediment loads and frequent channel changes (Xu et al, 1996).
The structure of the crustal basement has controlled the scale of palaeochannel development and the tectonics of the region have influenced changes of the ancient river systems and channels which, although now buried by sediments, continue into the Bohai and Yellow seas.
Thus, the entire Bohai and Yellow Seas are loaded with sediments. However, since both the Bohai and Yellow Seas are relatively shallow and the underwater slopes are not steep, tsunamis generated from submarine landslides (triggered by earthquakes or other disturbances) would tend to be localized.
Satellite photo showing the heavy load of sediments from major rivers flowing into the the Bohai, Yellow and South China Seas.
Oil platform in the Bohai Sea. Numerous more oil platforms exist in the Yellow as well as the South China Seas. At least 7 nuclear power plants are either operating or under construction along China's east coast, thus the vulnerability to earthquakes and marine disasters (including tsunamis from local or distant sources), is substantial.
References and Additional Reading
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.
Chen Guo-guang 1, Xu Jie 1, Ma Zong-jin 1, Deng Qi-dong 1, Zhang Jin 1 and Zhao Jun-meng, 2007. Recent tectonic stress field and major earthquakes of the Bohai sea basin, Acta Seismologica Sinica, Volume 17, Number 4 / July, 2004, pp.438-446, Published by Springer in Earth and Environmental Science, 2007.
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.
Davis, G. A., Zheng, Y., Wang, C., Darby, B. J., Zhang, C., and Gehrels, G., 2001, Mesozoic tectonic evolution of the Yanshan fold and thrust belt, with emphasis on Hebei and Lianoning provinces, northern China: Memoir - Geological Society of America, v. 194, p. 171-197.
Hendrix, M.S., and Davis, G.A., 2001, Paleozoic and Mesozoic tectonic evolution of central Asia: from continental assembly to intracontinental deformation: Boulder, Colo., Geological Society of America, vi, 447 p.
Keilis-Borok, V. I. and Soloviev, A., (Edis.), 2003. Nonlinear Dynamics of the Lithosphere and Earthquake Prediction. Springer-Verlag, Berlin-Heidelberg.
Ma, L. and Gao, X., 1996. The state of intensive monitoring and prediction at the Metropolitan Area before Asian Game in 1990. He, Y. N. (Ed.), The Selected Papers of Earthquake Prediction in China, Dedicated to the 30 th International Geological Congress, Seismological Press, Beijing, 255-259.
Mei, S. R. (Ed.), 1982. Tangshan Earthquake in 1976. Seismological Press, Beijing (in Chinese).
Yin, X. C., Wang, Y. C., Peng, K. Y. and Bai, Y. L., 2000. Development of a new approach toearthquake prediction: Load/Unload Response Ratio (LURR) theory. Pure Appl. Geophys. 157, 2365-2383.
Yin, A., and Nie, S., 1996, A Phanerozoic palinspastic reconstruction of China and its neighboring regions, in Yin, A., and Harrison, T. M., eds., The Tectonic evolution of Asia: Cambridge [England] ; New York, Cambridge University Press, p. 442-485.
Zhongliang Wu and Shaoxian Zang, 1989. Source parameters of bohai earthquake, July 18, 1969 and yongshan earthquake, May 11, 1974 determined by synthetic seismograms of teleseismic P waves. Acta Seismologica Sinica. Seismological Society of China. Volume 5, Number 1 / February, 1992, pp. 1993-1344 (Online) Issue
Zhang, Z.M., Liou, J.G., and Coleman, R.G., 1984, An outline of the plate tectonics of China: Geological Society of America Bulletin, v. 95, p. 295-312.
Zhang, G. M. and Ma, L. (Eds.), 1993. Study on the Datong-Yonggao Earthquake. Seismological Press, Beijing (in Chinese).
Zhang, Y. X., Liu, G. P., Chen, Q. F., Ma, L. and Yang, W. Z., 1998. The feature of anomaly evolution before Shunyi M S 4.0 earthquake and estimation for the tendency of the quake by LURR. Earthquake 18(1), 49-56 (in Chinese).
Zhang, Y. X. and Liu, G. P., 2000. Study on characteristics of anomalies near by epicenter of Zhangbei M S 6.2 earthquake and their spatial and temporal evolution. Earthquake 20(1), 53-58.
Zhu, F. M. and Wu, G., 1982. The Haicheng Earthquake in 1975. Seismological Press, Beijing (in Chinese - English abstract).
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.
Wang Jian, 2007. Historical earthquakes and a tsunami in Bohai Sea. Journal Acta Seismologica Sinica. Publisher Seismological Society of China ISSN 1000-9116 (Print) 1993-1344 (Online), Volume 20, Number 5 / September, 2007.
Xu Qinghai, Wu Chen, Yang Xiaolan and Zhang Ningjia, 1996. Palaeochannels on the North China Plain: relationships between their development and tectonics. Studies of the Palaeochannels on the North China Plain, Geomorphology, Volume 18, Issue 1, December 1996, Pages 27-35
Zhonghao Shou, 1999. "The Haicheng Earthquake and Its Prediction", Science and Utopya 65, page 34, November 1999" (in Turkish, English abstract)
Wu and Shaoxian Zang, 1992, Seismological
Society of China (Acta
Seismological Sinica Publisher), ISSN
1000-9116 (Print) 1993-1344 (Online) Issue Volume
5, Number 1 / February, 1992
Each Asian marginal sea is fed by a river system, many of which have their head-waters in the Tibetan Plateau. These are some of the largest rivers in the world, including the Yellow, Yangtze, Pearl, Red, Mekong and Irrawaddy.
China is situated at the west bank of the Pacific Ocean
with a shoreline measuring 18,000 kilometers. The tsunami
has a little influence on the coastal areas due to the
holding back by the Ryukyu Islands and the Southeast
Asian countries and the broad continental shelf.
Since the founding of new China three times of tsunami have been monitored in the coastal areas of China.
The first is the tsunami occurred on July 18, 1969 in the middle of the Bohai Sea caused by a strong earthquake with a magnitude of 7.4 bringing a certain losses to Tangshan, Hebei province.
The second is the tsunami occurred on January 1-2, 1992 at the southern tip of the Hainan Island. The tidal height was 0.78 meters measured by Yulin Tidal Gauge Station while the tidal height was 0.5-0.8 meters at the Sanya port, causing certain losses. The third was occurred at the Taiwan Straits in 1994 with no losses.
Earthquake and tsunami hazards exist in the Indian Ocean, Andaman Sea, the Philippine Sea, Bohai Sea, East China Sea, South China Sea, Java Sea, Sulawesi [Celebes] Sea, Mindanao Sea, and Sulu Sea. The tsunami travel times across these seas are, in many cases, on the order of only an hour or two and consequently require a dense network of instrumentation and real or near real time data
Earthquakes in the Beijing Area - According to the historical records, there have been 41 earthquakes with magnitude larger than M S 5 (including aftershocks) in the metropolitan area around Beijing since 1900(Figure 4).
From Figure 4, we can see an interesting phenomena that the interval betweeneach two neighboring earthquakes(or earthquake groups) with magnitude more than 5.0 was about 11 years, which reflects the earthquake cycle of about 11 years in this region. Figure 4. Time series of earthquakes larger than M S 5 in China Metropolitan Area around Beijing (including aftershock of Tangshan M S 7.8 earthquake)
From 1970, the seismic network has been set up gradually and we have obtainedearthquake catalogue with magnitude bigger than M L 2.0 (Figure 2). According to thecatalogue, 1094 earthquakes with magnitude larger than M L 4.0 were recorded in this region (including aftershocks).
Figure 5a shows the distribution map of earthquakes larger than M L 4.0 in andaround the metropolitan area (including aftershocks) since 1970. There are three significant earthquake clusters in this map. The first one was the Tangshan M S 7.8 earthquake (39.41°N, 118.00°E) series from July 28, 1976, which lies in the east region.
The second one was the Datong-Yanggao M S 6.1 earthquake (39.95°N,113.82°E) series from October 18, 1989, which lies in the west region.
The third onewas the Zhangbei M S 6.2 earthquake (41.1°N, 114.30°E) series from January 10, 1998, which lies on the north-west edge of the metropolitan area. Figure 5(a) Distribution of earthquakes larger than M L 4.0 in and near the Metropolitan Area from 1970 4.0?4.95.0?5.96.0?6.97.0?7.9
Figure 5b is the time series of earthquakes larger than M L 4.0 in Figure 5a. We cansee in this figure that there were many aftershocks of the Tangshan M S 7.8 earthquake during the periods from July 28, 1976 to 1979, and many aftershocks of the Datong-Yanggao M S 6.1 earthquake from October 18, 1989 to 1991, as well as many aftershocks of the Zhangbei M S 6.1 earthquake from January 10, 1998 to 1999.
If we only considerthe mainshocks, about 2 earthquakes larger than M L 4.0 occurred in this area every year.In recent ten years, about 20 earthquakes with magnitude bigger than M L 3.0,about 200 earthquakes with magnitude bigger than M L 2.0, and about 600 earthquakeswith magnitude bigger than M L 1.0 occurred in this region every year.
Figure 5(b) Time series of earthquakes larger than M L 4.0 in and near the Metropolitan Area around Beijing from 1970 3. Review of the Practice and Test of Earthquake Prediction The practice and test of earthquake prediction in China began from 1966 after the Xingtai M S 7.2 earthquake (the 9th earthquake in Table 1). From then on, North China underwent a period with high seismicity ever since 1900 (the 9 th , 10 th , 11 th and 12 th earthquakes occurred successively, as shown in Table 1). The fortunate thing is that,there were many foreshocks several days before the Haicheng M S 7.3 earthquake in1975 apart from other seismicity, geophysical and geochemical anomalies (Zhu andWu, 1982), so a successful prediction was made by seismologists and issued by the local government of Liaoning Province at that time, which reduced the disaster and saved thousands of lives.
the Tangshan M S 7.8 earthquake occurred one and ahalf
years later on July 28, 1976, despite many abnormal variations
of geophysical and geochemical parameters had been obtained
before the quake, seismologists still expected the foreshocks
which were taken as a prerequisite induced from the experience
of the Haicheng M S 7.3 earthquake prediction. Unfortunately,
there wereno foreshocks but earthquake quiescence before
the Tangshan earthquake, hence the failure of prediction
before the Tangshan M S 7.8 earthquake and the failure
456 more than 240000 deaths (Mei, 1982).
. From then on, two major earthquakes with magnitude larger than M S 6 occurred in this region, the Datong-Yanggao M S 6.1 earthquake in 1989 and the Zhangbei M S 6.2 earthquake in 1998 (Figure 5a). In addition, there were 10earthquakes of M S 5.05.9 in this region, two of them are late aftershocks of the Tangshan earthquake, six of them are foreshocks and aftershocks of the Datongearthquake, and one of them is aftershock of the Zhangbei earthquake.
is onlyone independent earthquake among the 10 earthquakes
of M S 5.05.9 in this regionfrom 1980, the Fengzhen M
S 5.6 earthquake in 1981 (Table 2). Table 2. Earthquakes
larger than M S 5 in the Metropolitan Area around Beijing
from 1980 No. Earthquake Datea-m-d Latitude ( ° N)Longitude( ° E)
M S 1 Fengzhen 1981-8-13 40.51 113.40 5.6 2 Datong 1989-10-18
39.51 113.40 5.7 3 Datong 1989-10-19 39.96 113.72 6.1
4 Datong 1989-10-19 39.51 113.40 5.6 5 Datong 1989-10-19
39.51 113.40 5.1 6 Datong 1989-10-23 39.51 113.40 5.2
7 Datong 1991-3-26 40.01 113.81 5.8 8 Tangshan 1991-5-30
39.51 118.21 5.1 9 Tangshan 1995-10-6 39.81 118.50 5.0
10Zhangbei 1998-1-10 41.1 114.3 6.2 11Zhangbei 1999-3-11
41.2 114.6 5.6 12Datong 1999-11-1 39.8 113.0 5.6 Among
these twelve earthquakes, we take number 1?2, 7?12 earthquakes
asindependent events those could be tested whether they
were forecasted or not.Among these eight strong earthquakes,
only the Zhangbei earthquake wasforecasted in medium-term
scale in official document. Figure 6 is the annual PotentialSeismic
Regions (shadows) for 1998 and earthquakes larger than
M S 5(solid circles) in 1998. From this figure, we can
see that the Zhangbei earthquake occurred at the edgeof
a potential region forecasted beforehand. Many anomalies
were detected in different time and space scale before
thisearthquake (Zhang, 1999), such as earthquake belt
of M4 during 1995?1997 (south-east of the epicenter),
high seismic swarms (6 in 1996 and 11 in 1997 in north
China),seismic quiescence in north China (none earthquake
of M4 occurred in north China during 110 days before
the quake), high weekly frequency of anomalies in
457 metropolitan area two months before the quake, a few number of abnormal suddenchanges of observatory curves in the metropolitan area. Figure 6. Annual potential seismic regions (shadows) for 1998 and earthquakes larger than M S 5 (solid circles) in 1998 For example, the cumulative number of anomalies increased to 46 out of thetotal number of 225 observatory items in the metropolitan area before the Zhangbei M S 6.2 earthquake (Figure 7), and the anomalies distributed mainlyaround the epicenter (Zhang, 1999; Zhang and Liu, 2000). The anomalies include georesistivity, crust deformation, ground water level, water radon content, watermercury content, etc. The imminent earthquake anomalies were generally the sudden change of water level, soil CO 2 content and the damaged tidal shape of cubic strain, and so on. Figure 8 shows the soil CO 2 curve of Huailai station (40.33°N, 115.53°E), whichis about 150km from the epicenter of Zhangbei M S 6.2 earthquake and 500km fromBaotou M S 6.4 earthquake (40.8°N, 109.6°E). Figure 7. Weekly frequency curve of real time anomalies in metropolitan area
458 Figure 8. Density of soil CO 2 in Huailai station about 150km fromthe epicenter of Zhangbei M S 6.2 earthquake From another point of view, there were two earthquakes (Nos.11 and 12 in Table 2) in 1999, but no related annual potential seismic regions were identified for this year. Several months before these two earthquakes, some kind of seismic anomaliesand geophysical anomalies were detected, and some rough forecasts were made byseveral researchers, but the relationship between these anomalies and these twoearthquakes was still unknown. The fact shows that we have not obtained the essenceof seismogenic process at present. Although a lot of anomalies in different time andspace scale were recorded, we are not able to tell the difference between medium-term anomalies and short-term anomalies. Comparing the locations of the eight strong earthquakes in Table 2 and the distribution map of observational station in Figure 3, we can see that Nos.1?4 andNo.10?12 earthquakes located in the west part of the Metropolitan Area with lowermonitoring capacity, and Nos.8?9 earthquakes located in the east part of the Metropolitan area with higher monitoring capacity. All these strong earthquakes werenot surrounded by well-distributed observatory network, so we could only obtain lesspart of earthquake anomaly information when these strong earthquakes occurred. Thismight be one of the reasons of the difficult earthquake forecast. However, manyanomalies were recorded before and after these earthquakes although no exact prediction was issued (Zhang and Ma, 1993; Zhang, 1999). An obvious phenomenon is that the late aftershocks of the Tangshan M S 7.8 earthquake are more difficult to forecast because there were less anomalies before them.For example, before the No.9 earthquake in Table 2, few earthquake anomalies weredetected, as shown in Figure 7 (Tangshan M L 5.4 earthquake). Some mechanics weresupposed for this phenomenon. One of the supposed mechanics is that the Tangshanarea is a cracked region after the Tangshan M S 7.8 earthquake, and lower stress couldbe accumulated in the cracked region, hence the less earthquake anomalies before the late aftershocks.
459 However, several successful earthquake forecasts have been made by CAP, CSB before M L 4?5 moderate earthquakes in this area. The famous one is the Changping(40.08°N, 116.37°E) M L 4.5 earthquake on September 22, 1990 (Beijing Time), whichis the nearest earthquake with magnitude bigger than M L 4.0 apart from Beijing since 1980, as shown in Figure 9. This earthquake happened just on the Opening Ceremony of the 11 th Asian Games in Beijing. Abnormal phenomena around the epicenter weredetected several weeks ago and the number of the precursors increased before thequake. A formal report of earthquake forecast was submitted to the government one week before the Ceremony (Ma and Gao, 1996). Figure 9. Earthquakes with magnitude bigger than M L 4.0 in the Metropolitan area from 1980 Other successful cases are the Shunyi (40.17°N, 116.50°E) M L 4.5 earthquake onDecember 16, 1996 (Zhang, et al, 1998); the Zhangjiakou (40.70°N, 114.87°E) M L 4.7earthquake on May 25, 1997; the Shacheng (40.48°N, 115.53°E) M L 4.4 earthquakeon August 3, 2002, etc. The significant abnormal phenomena before each of these moderate earthquakes are different. For example, the main anomaly before the ShunyiM L 4.5 earthquake on December 16, 1996 is an obvious north-south earthquake belt; the main anomaly before the Zhangjiakou M L 4.7 earthquake on May 25, 1997 is theincrease of weekly anomalies (as shown in Figure 7), and the main anomaly beforethe Shacheng M L 4.4 earthquake on August 3, 2002 is the earthquake belt and seismic gap near the epicenter (as shown in Figure 10).Comparing Figure 9 with Figure 3, we can see that most of the successfulforecasted moderate earthquakes were surrounded by well-distributed station network.This might be one reason why we could make relative successful forecasts. Anotherreason is that there were 2?4 earthquakes with magnitude bigger than M L 4.0 everyyear in the metropolitan area, so we have more chances to diagnose the abnormalchanges of seismicity and observed parameters before these earthquakes, and obtainmore experiences to judge the earthquake precursors. However, these forecasts are not accurate ones because that the forecasted time,location and magnitude are not accurate but approximate.
460 Figure 10. Seismic gap before Shacheng M L 4.4 earthquake on Aug.3, 2002. Gray circles:earthquakes during May16, 2002-July 1, 2002. Solid circles: earthquakesduring July 2, 2002-August 3, 2002. Dark dots: cities (Detected before the quake and taken as an evidence for the earthquake forecast) 4. Earthquake Prediction Approaches in the Metropolitan Area In Chinese mainland, earthquake monitoring and prediction is a routine daily work. All possible approaches are tried to apply in earthquake prediction, including seismicitypattern (seismic gap, belt, etc.), seismic parameters including LURR (Yin et al., 2000), b value, earthquake frequency, etc., geophysical parameters (V P /V S , crust deformation,gravity, cubic strain, georesistivity, geomagnetism, ground water level, etc.), geochemical parameter (water radon, water mercury, soil CO 2 , etc.). After more than 20 years of earthquake prediction practice and test in the Metropolitan Area, we have groped some phenomena related to future earthquake location, magnitude and time. 4.1. Phenomena related to the future earthquake locationEarthquake tends to occur near place with inhomogeneous structure;If an obvious earthquake occurs, it might be a foreshock with a successivemainshock in the same place; Earthquake tends to occur at places with anomalous seismic patterns: earthquakebelts; seismic gap;Earthquake tends to occur at or near the region with anomalous seismicparameters (e.g., b-value, earthquake frequency, LURR). For example, beforeZhangbei M S 5.6 earthquake on March 11, 1999 (No. 11 earthquake in Table 2), there existed an anomalous LURR region near the epicenter during the period from August,1998 to January, 1999. Figure 11 gives the spatial scanning contour of LURR in the Metropolitan Area during this period. 1.0?1.9 2.0?2.93.0?3.94.0?4.95.0?5.9
461 4.2. Evaluation of future earthquake magnitudeThe magnitude of the coming earthquake is about 2 larger than the foreshock oraverage magnitude on earthquake belt; The G-R relation after the former major earthquake could reflect the magnitudeof future earthquake; The magnitude of the coming earthquake is related to the last time, magnitude,and distribution scale of earthquake anomalies. Figure 11. LURR contour during the period from Aug. 1998 to Jan. 1999. Solid circles: the west one is Zhangbei M S 5.6 earthquake on March 11, 1999; The east one is Tangshan M L 4.4 earthquakeon Jan.9, 1999. Earthquake tends to occur near region with dense observed anomalies 4.3. Prediction of future earthquake time If there is foreshock, the major earthquake will come several days later; The macroscopic anomaly often occurs shortly before the future earthquake;Many ground water anomalies often occur simultaneously shortly before the future earthquake;Earthquake tends to be triggered by outside environment such as the Earth tides,Earth rotation and geomagnetic field;Time series of some seismic parameters show anomaly shortly before thecoming quake. 5. Discussion on the Feasibility of Earthquake Prediction The above retrospection of earthquake prediction in the China Metropolitan Area gives us a conception that earthquake prediction is just at the beginning of a longmarch. We have discovered some abnormal phenomena those might be related to
462 earthquake generation, but the abnormal phenomena before each earthquake might bedifferent. These might be caused by the complexity of the process of earthquakegeneration (e.g., Keilis-Borok and Soloviev, 2003). As revealed by rock mechanicsexperiments, the variation of stress and strain before the failure of the sample depends on the loading pattern, rock property, temperature, etc. The environment of the sourceis more complex, hence the complex feature of the anomalies before each kind ofquakes. Although the pattern of abnormal phenomena before each earthquake is different, there is also the common abnormal phenomenon before most of the quakes, for example, the number of anomalies increases before most of the shocks. These cases encourage us to persist in the practice and study of earthquake prediction in this area. Although we are not able to issue an exact earthquake prediction at present, we canmake an approximate forecast which is very important to reduce the earthquakedisaster. As more information of the seismogenis process be gathered by high technology such as GPS, RS, and more detailed structure, property, stress state of thecrust are revealed, the prediction of earthquake could be more quantitative.
Since the 1950s, 7 tsunami events have been recorded in China.
Date Origin Earthquake
Tsunami height above
normal tide level
5/11/1952 Kamchatka 9.0 0.15 m
23/5/1960 Chile 9.5 0.3 m
18/7/1969 Bohai Sea 7.4 1~2 m
4/3/1985 Chile 7.9 < 0.1 m
24/6/1988 Luzon Strait 5.7 0.3 m
4/1/1992 Hainan Island
3.7 0.8 m
16/9/1994 Taiwan Strait
7.3 0.5 m
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