Chen Lijun, Chen Xiaofeng, Wan Fangfang, Ouyang Chengxin
Earthquake Administration of Hunan Province, 410004 Changsha,China
Abstract:The precursors of seismic activity characteristics under crust before crust strong earthquake magnitude 7 and more in two districts of the west coast of theUnited States(San Francisco and Los Angeles) were studied in this paper according to the principle of Seismo-geothermics and the ANSS catalogue of earthquakes. An earthquake predictive method was also proposed by using under crust seismic activity characteristics as the precursors of crust strong earthquake. The tendency of future strong earthquake activity of the two districts can be forecasted based on the enlightenment and the train of thought which need to be the test of practice.
Keywords:Seismo-geothermics, earthquake, prediction method, west coast, theUnited States
*Thefunded projects subject of Old Experts Research Foundation of China Earthquake Administrationin , serial: 29.
1 Introduction
In recent decades, people accustomed to using the "collision" and "subduction" to explain the genesis of earthquakes and volcano. It’s not a truth.
By the research of global focal depth, a new Seismo-geothermics (Chen Lijun, 2000, ) was found deep earthquake activity in bottom-up layer-by-layer driven trends which composed of the main energy of strong earthquake and volcano activity. 24 seismic cylinders were defined and formed an M type global heat engine belt which was from the South Sandwich Islands to the Mediterranean, then Himalaya mountains,Indonesia,Tonga,Philippines, along the North Pacific Ocean to South America, return to the South Sandwich Islands, and this heat engine belt controls more than 90% of the shell earthquake and volcano activity on the Earth. The action of the seafloor spreading and the inheritance of the translational activity of the mid-ocean ridge by the function the change of angular velocity of the Earth rotation can only result in some shallow earthquakes and a little of volcano activity, forming a W type global cooling belt from the Atlantic Ocean to India Ocean and the Pacific Ocean. The global heat engine belt and the cooling belt buckle each other and a few centimetres per year of ground motion observed by global GPS network may regulate the running of two belts with the way of continental drift, see /seisman/ (Fig.1).
According to the principle of Seismo-geothermcs, the seismic activity under crust may become the precursors of strong earthquakes in the crust.
North America belongs to the heat engine belt and it is an alternative place to verify the above ideas because of the perfect earthquake catalogue and the crust strong earthquakes activity of magnitude 7 and more in North America.
Fig.1 The draft map of two systems of global tectonics
2 The selection of thestudy area
The study area in this paper is from 104º to 141º west and 0º to 70º north, respectively and the epicentre distribution map of magnitude 3 and more are shown in Fig. 2.
As can be seen in Fig. 2, there were two earthquakes above magnitude 7 along the northern coastline occurred in the early 1970s and the earthquake catalogue data before the earthquakes were not completed enough. Also, the activity zone of the 2 earthquakes above magnitude 7 or greater in southern tip had been out of the area. To carry out summarizing the seismic case, the seven earthquakes of magnitude 7 or greater were chosen only in yellow boxes and the catalogue of the seven earthquakes is shown in Tab.1.
It should be noted that the line of San Andreas fault (from http://pubs.usgs.gov/) existed exactly. For convenience to study, the action was divided into two regions called San Francisco district and Los Angeles district, respectively. The San Francisco area is from 120º to 130º W and 32º to 52º N, while Los Angeles area is from 110º to 120º W and 20º to 50º N. The two regions correspond to the north or south sections of the San Andreas fault and the seismic activity in 2 sections is slightly different.
Fig.2 The epicentre distribution map of magnitude 3 and more in the west coastline in North America.
(From ANSS catalogue, 1960.1～.12)
Tab.1 The catalogue of shell earthquakes magnitude 7 and more in California
Date
Time
Lat. (°)
Lon. (°)
Depth(km)
Magnitude
Mag Type
19801108
10:27:33
41.0842
-124.6157
14.64
7.20
Unk
19891018
00:04:15
37.0362
-121.8798
17.43
7.00
ML
19920628
11:57:34
34.2000
-116.4370
0.97
7.30
Mw
19940901
15:15:53
40.4020
-125.6800
10.00
7.00
Ms
19991016
09:46:44
34.5940
-116.2710
0.02
7.10
Mw
0615
02:50:54
41.2920
-125.9530
16.00
7.20
Mw
0404
22:40:41
32.2163
-115.3005
10.00
7.20
Mw
3The case summary and forecast analysis in the San Francisco district
Fig 3 shows the earthquake focal depth timing diagram in San Francisco. The crustal thickness of the west coast in theUnited Statesis approximately 20 ~ 30 km according to the W.D. Mooney ().
As can be seen in Fig.3, it indicated that the shell earthquakes mostly concentrated within 20km, under crustal earthquakes almost located under 35km, and the others can be seen as down crustal earthquakes.
Therefore, it suggests that there is a bottom-up layer-by-layer driven process of seismic activity under the depth of 35 km before each strong earthquake magnitude 7 since 1970. The four slashes showed in Fig.3 indicate the drive rate and the annual rate is several kilometres driven upward.
Fig.3 The earthquake focal depth timing diagram (M≥3.5) in the San Francisco district
Fig. 4 shows the spatial distribution of earthquakes over magnitude 3, or 3.5 under the depth of 35 km happened in 1980, 1989, 1994 and respectively in San Francisco.
By comparing with two charts in Fig 4, it’s easy to find the locations of future earthquakes that likely to occur.
Therefore, we can estimate that the time of future earthquake may occur by using the timing diagram of focal depth, and the likely locations of a future earthquake by using the contrast diagram of the spatial distribution of a characteristic magnitude of earthquakes. The earthquake over magnitude 7 is the target and the three elements of earthquake prediction can bring an estimation with greater confidence.
Based on this idea, the distribution image of earthquakes under shell since can be proposed in Fig 5. As can be seen from the graph, the possibility of earthquake magnitude above 7 along the Northern San Andreas fault is very little in the next 1 ~ 2 years.
Fig.4 The contrast diagram of the spatial distribution of earthquakes magnitude 3 or 3.5 and more under the depth of 35 km
a) before the earthquake of magnitude 7.2 in 1980 in San Francisco(1970-1980).
b) before the earthquake of magnitude 7.0 in 1989 in San Francisco(1980-1989).
c) before the earthquake of magnitude 7.0 in 1994 in San Francisco(1981-1994).
d) before the earthquake of magnitude 7.0 in 1994 in San Francisco(1990-1994).
e) before the earthquake of magnitude 7.2 in in San Francisco(1995-).
Fig.5 The contrast diagram of the spatial distribution of earthquakes magnitude 3 (a) or 3.5 (b) more under the depth of 35 km in - in San Francisco.
4The case summary and forecast analysis in the Los Angeles district
Fig.6 shows the earthquake focal depth timing diagram in Los Angeles.
There is a bottom-up layer-by-layer driven process of seismic activity under the depth 35km before every strong earthquake magnitude 7 since 1980, which is similar to San Francisco. The three slashes in Fig.6 indicate that the drive rate and annual rate are several kilometres driven upward, and the rate-driven is a little bigger than San Francisco.
As can be shown in Fig.7, it indicates that the spatial distribution of earthquakes over magnitude 2 or 2.5 under the depth of 35 km happened in 1992, 1999 and in Los Angeles.
Compared with the two charts in Fig.7, the possible locations of the coming earthquake can be found easily. The characteristic of the area is that the strong shock always happens at the southern San Andreas fault no matter the distribution of under shell earthquake. It may contribute to choosing the possible place of a strong earthquake in the future.
After the powerful earthquake in , it should be noted that there still exists the earthquake activity beneath the crust which need be paid attention further (see Fig.6).
Fig.6 The earthquake focal depth timing diagram (M≥3.0) in the Los Angeles district
Fig.7 The contrast diagram of the spatial distribution of earthquakes magnitude 2 or 2.5 and more under the depth of 35 km
a) before the earthquake of magnitude 7.3 in 1992 in Los Angeles(1980-1992).
b) before the earthquake of magnitude 7.1 in 1999 in Los Angeles(1992-1999).
c) before the earthquake of magnitude 7.2 in in Los Angeles(1999-).
5Conclusions andAcknowledgment
According to the principle of Seismo-geothermics and the ANSS catalogue of earthquakes in this paper, an earthquake predictive method was studied based on the precursors of seismic activity characteristics under crust before crust strong earthquake magnitude 7 and more in two districts of San Francisco and Los Angeles in the west coast of the United States, some very good enlightenment and forecasted the future strong earthquake activity tendency of the two districts were obtained using the train of thought which need to be the test of practice.
Based on the analysis in this paper, because of California region in the global heat engine belt on the Earth with the maximum depth of up to 650km of earthquakes over magnitude 2, the energy of shell strong earthquake activities mainly comes from the deep Earth, and there is a bottom-up layer-by-layer driven. It is certainly that strong earthquakes can be affected by the control of surface fracture, the rising energy from deep Earth should find a location which is released and convenient for stress concentration. The surface motion of a few centimetres every year observed by GPS can contribute to the movement and stress accumulation of surface tectonics, which can play the only role of support and boost of a strong earthquake.
The earthquake catalogue ANSS in this paper is obtained from http: / / / web pager, we hereby express our thanks.
Reference
Chen Lijun. Research of earthquake focal depth and strong seismicity inChina. 2000, Seismology and Geology. Vol. 22, No. 360-370
Chen Lijun. Theory and Applications of The Seismo-Geothermics. Inland Earthquake, , Vol. 26, No. 2, In Press.
W.D. Mooney, Zheng Wenjun. The continental crust (two), Translated world seismology, , No.2, p79-84
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(The first draft, .1.6)
初见：《湖南地震》，总第35期，p.90-98
美国西海岸地震预测方法研究
陈立军 陈晓逢 万方方 欧阳承新
湖南省地震局，长沙，410004
摘要:本文采用ANSS地震目录，按照地震地热说的原理，研究了美国西海岸旧金山和洛杉矶两个分区壳内强震之前的壳下地震活动特征，提出了利用壳下地震活动作为壳内强震前兆的一种预测方法，得到很好的启示并按此思路分别对两个分区未来的强震活动趋势进行了预测，有待实践的检验。
关键词: 地震地热说，地震，预测方法，西海岸，美国
