Wol.15 No.6 (595-606)
ACTA SEISMOLOGICA SINICA
Nov., 2002
Article ID: 1000-9116(2002)06-0595-12
The seismicity research in the sub-regions of Chinese mainland using strain accumulating and releasing model* MAHong-sheng(~_)
LIUJie(J~J
~)
ZHANGGuo-min(~)
LILi(@
ffff)
Center for Analysis and Prediction. China Seismological Bureau, Beij'ing 100036, China Abstract
The sub-regions are divided for the seismicity of the Chinese mainland based on the hypothesis of the active crustal blocks and the division of the active boundaries. On this result, the seismicityof each active crustal blocks are studied by calculating the accumulated and released strain of the earthquakes based on strain accumulating and releasing model, and the different seismicity stages of the sub-regions are discussed basically. Finally we have discussed the premise of the model application and the potential problems of the model results. Key words: strain accumulation and release; active crustal block; seismicity; seismic active period CLC number: P315.72"7 Document code: A
Introduction Lots of researches suggest that the seismicity is irregular in the space and unsteady on the time. The former behaves as that the earthquakes usually are distributed in bands or zones, the latter behaves as that the seismicity has the active and placid alternant stages (high and low). Analyzing the seismicity of Chinese mainland shows that the distribution of strong earthquakes indicates different distributing pictures in space in different periods. According to strain releasing plot, the activity of strong earthquakes could be divided into some periodic cycles. Every cycle includes one active stage of strain releasing and one low stage of strain releasing. The figure is rather steady, and each cycle has its relatively stable main region. The strain accumulating and releasing with the time decides the active period of the strong earthquakes. QIU and GAO (1986) had not only plotted out seismicity phases of the Chinese mainland and sought after the transitional character of the main regions of strong earthquakes in every phase, by means of analyzing systematically the seismicity parameters (frequency, energy, strain release and b value etc) of the strong earthquakes with magnitude above 6, but also proposed her opinion on the earthquake tendency in future. HUANG and CHEN (1996) had also used the strain accumulating and releasing curve to discuss the tectonic movement and the relationship of the placid-active phenomena of every main seismic zone in China. In this research, we have divided the seismicity of Chinese mainland into several sub-regions, which is based on the hypothesis of
" Receive date: 2001-07-13: revised date: 2002-03-25; accepted date: 2002-04-08 Foundation item: The Developmentand Planning Project of National Important Base Research on the Mechanism and Forecast for Continental Strong Earthquake (G 19980407)
596
ACTA SEISMOLOGICASINICA
Vol.15
the active crustal blocks and the division of the active boundaries. On this result, we have used the strain accumulating and releasing model to study the seismicity of the divided sub-regions by calculating strain accumulation and release of the earthquakes. We have studied the different seismicity of the divided sub-regions and compared the seismicity of each sub-region. Finally we have discussed the earthquake tendency of every sub-region in future.
1 The model The strain of a block is a physical word closely to the tectonic stress and the seismic process, which is often used in the research of seismic stage division (XIA, 1987). The strain released by one earthquake is based on the experiential formula between energy and magnitude by Gutenberg, Richter (1956) and Kanamori (1977) lgE =1.5Ms + 4.8
(1)
The strain can be got by the square root of the energy. E means the energy (unit in J), and Ms means the magnitude by surface wave. When we study strain accumulation and release in one region, we must consider the integrality of the seismic data in the region. It involves two aspects. One is the relative integrality in time, which means that the data cover at least one complete seismic cycle. The other is the relative integrality on space, which means that the data should match with the seismogenic tectonic block (seismic zone) on the space. By analyzing the earthquake serial character in time, the seismicity has the character of relative placidity and notable activity altering. Thus, we should take into account this character when we consider the integrality of the seismic data. As the data being relatively integrate, we propose that the total accumulated strain should be equal to the total released strain in an independent and complete system for one or several seismicity cycles. In the process of crust movement, the strain of the active tectonic block (equal to a seismogenic system) is accumulated with time. When the strain reaches the utmost intensity of the rock, the strain may be released as the earthquakes in order to get another new balance. The seismic placid phase is the accumulating strain phase, whose character is that the accumulated strain is far greater than the released; for the active phase, the character is that the released strain is far greater than the accumulated. But, in a complete earthquake cycle, the total accumulated strain should be generally accord with the released. Based on these characters, we use the strain accumulating and releasing model to discuss the seismicity of each earthquake sub-region based on the results by strain accumulating and releasing curve. The reason that the placid phase is taken as the beginning of a cycle is that there are fewer strong earthquakes in the placid phase and the strain can be accumulated. When the strain is accumulated to some degree, earthquakes begin to occur and then work up to climax. The stain released in the active phase is related to the strain accumulated in the placid phase to some extent. So, it is quite reasonable taking the placid phase as the beginning o f a seismicity cycle (SHI, et al, 1974). ZHANG, et al (1993, 1995) and ZHANG and LI (1997) have particularly studied the grouping seismogenic model of tectonic blocks in detail, and given theoretic curve as Figure 1, which includes the level change curve of the total strain with time in seismogenic system (Figure l a), M-t plot of seismicity temporal distribution in seismogenic system (Figure lb), in which t is the experiment time of grouping seismicity simulated by computer model. In Figure 1, we take the beginning of the first cycle as the start and the end of the last cycle as the terminus, calculating the
No.6
MA Hong-sheng,et al: SEISMICITY RESEARCH IN SUB-REGIONS
597
total time of the whole process. Then we count the total strain released zx/-E-~-~,and the rate of the strain released in some time interval can be #- Y~' T
(2)
where T is the total time. Considering T includes several cycles, the accumulated strain is generally equal to the released. It is necessary to point out that ~ -
represents the released strain s
(Benioff, 1951), which is an approximate express method. Actually, E, oc/~oe2/2, where/~ is elastic coefficient. In our research, we take the/~ of one block as an constant, and use x ~ / t o represent the strain released of the i-th earthquake. This parameter just shows comparative value of strain releasing by earthquakes with different magnitude. There are some differences in the obtained results of different blocks. So s can be taken as the average rate of the strain accumulating in formula (2). Having the accumulated strain kt detract the practical released strain 3- x/~+, i
Nt,>
(3) i=1
we can get the G) which reflects the strain level in the time t. N ( t ) is the occurred earthquake number before the time t. By formula (2) and (3), we can work out the curve of G) changing with t. This curve is similar to the theoretic curve in Figure 1. It is clear that there are periodic fluctuations of seismicity. When the trend of the curve is up, it means that the strain energy is in an accumulating phase, 16.5;
(a)
/;
i
]6.0:
,+ t5.5 .E t4.5
14.0 1450
I
I
1500
1550
1500
1550
I
Year
I
I
1600
165,
1700
(b)
3
1450
I
Year
~
600
'
iI,,lll ,ul i
f
I
'
1650
v
i
r
I
i
1700
Figure ! The strain releasing curve and the M-t plot of the model (a) The strainreleasingcurvefrom 1450to 1730;(b) M-t plotfrom 1450to 1730
598
ACTA SEISMOLOGICASINICA
Vol.15
and the accumulating strain is larger than the releasing, which can be taken as a placid phase. When the trend of the curve is down, it means the strain energy is in a releasing phase, and the releasing strain is larger than the accumulating, which can be taken as an active phase.
2 The active crustal blocks in Chinese mainland and the division of seismicity sub-regions in our research The division of seismicity sub-regions in the research is based on the research of active crustal blocks. In Academic Progress on the Mechanism and Forecast for Continental Strong Earthquake in the First Two Years (ZHANG, ZHANG, 2000), Chinese mainland is divided into 5 first order active crustal blocks and 19 second order blocks. The 5 first order active crustal blocks include Qingzang plateau, Xinjiang, North China, South China and Northeast China. The 19 second order blocks include Tianshan, Junggar, Altay , Tarim, Qilian, Qaidam, Kunlun, Qiangtang, Lhasa, Himalaya, Chuan-Dian, Alxa, Erdos, North China, Yanshan, Northeast China, South China, Jiaodong and Southeast China Coast, which belong to the first order active crustal blocks. in our research, we divide Chinese mainland into 6 seismicity sub-regions, which are North China, Xinjiang, Southeast China seashore, Chuan-Dian, Tibet and Northwest China, which is showed in the thick lines in Figure 2, according to the first order crustal blocks. The seismicity sub-regions of North China, Xinjiang and Southeast China seashore are generally corresponding to the first order active crustal blocks of North China, Xinjiang and South China. Chuan-Dian sub-region includes the second order active crustal block of Chuan-Dian blocks and the southwest part of Yunnan province. In this sub-region, earthquake occurs frequently, and its tectonic background complex, so we regard it as one integrity. Tibet sub-region includes the second order active crustal blocks of Himalaya block in China, Lhasa block and Qiangtang block. Northwest sub-region consists of the second order active crustal blocks of Kunlun block, Qaidam block, QilJan block and AIxa block. 70*E
80 °
90"
t00 ~
110 °
120 °
130 °
I Figure 2
The seismicitysub-regions in Chinese mainland
140 ~
No.6
MA Hong-shenget al: SEISMIC[TY RESEARCH IN SUB-REGIONS
599
These 6 seismicity sub-regions basically contain all the shallow earthquakes with Ms>6 in Chinese mainland, but the accumulating and releasing strain of each sub-region are quite different in aspect of the deep structure, deformation process and geodynamics. This is just the reason that
why we study the seismicity in Chinese mainland by sub-regions.
3 The seismicity analyzing of each sub-region in Chinese mainland Because of the difference of seismogenic surrounding and earthquake record in different subarea, we adopt different starting time to calculate and analyze different sub-region considering the seismic data integrity. Based on this, we will discuss the phase of each sub-region, and analyze the seismicity of each sub-region by strain releasing rate g'. We shall approach these of every sub-region in the following.
In North China sub-region, the data of earthquake with Ms>6 are relative integrity since 1480 (HUANG, et al, 1994). One Ms=8.0 earthquake occurred in 1303, and in 1556 another Ms=8.3 occurred. When we choose the starting time, we have considered the strain accumulating process and the influence of large releasing. We regard the starting time as 1400 more reasonable, and its result is showed in Figure 3a. The accumulating-releasing curve approximately reflects two placid-active cycles, which count up to 600 years. In the first cycle, the strain had been fully released about 1700, and its strain value had reached to the lowest. The sum was 300 years from accumulating to releasing. In the second cycle, the strain has been releasing almost completely 8 . 0 X 10°
4. 0 ×
(a)
1o'i 0,0
- - .t. O X IOa
i {500
14 O0
8. OX IOJr
I {600
Year
f {700
J ]800
{ {900
i 2000
(b)
/
- - 4 . ON l0 s
--8. 0>~ 10d
J i 500
I I g00
i 1700
Year
I 1800
,/rI,lIll
~7
{300
I 4100
I 1500
L.
I
f 600 Year 1700
I 1900
,
I 2000
I,II,,II,ilI},,
I 8100
I 1900
t 2000
Figure 3 The strain releasing curve and the M-t plot in North China sub-region (a) The strata releasing curve from 1400 to 2000; (b) The strain releasing curve from 1480 to 2000: (c)M-t ptot from 1300 to 2000
600
ACTA SEISMOLOGICASINICA
Vol.15
since 1700 up to now. Having the two relatively integrate records, we can review the seismicity of North China sub-region to other sub-regions by comparing its k. In North China sub-region, =5.9x 106 JI/2/a, which is equal to occur 0.7 earthquakes with Ms=6 each year. We should point out that the et,~is an comparative value, of which et0~=0. The data of earthquake with Ms=5 in Southeast China Seashore sub-region is comparative complete since AD 1500. At the same time, because there had been no earthquake of Ms=5 from AD 1300 to AD 1400, we choose 1400 as the starting time in Figure 4. Its earthquake data are quite complete and its two cycles are clear as well. Especially in the second one, the strain has been accumulated quite a long time and released quite completely, so the seismicity is rather low now. Its k=l.6×106 J=/2/a, which is equal to occur 0.2 earthquake with Ms=6 every year. Comparing with the average strain releasing rate of North China sub-region, we can obtain the conclusion that the strain accumulating of North China sub-region is a little more rapid than that of Southeast China Coast sub-region, and the seismicity of North China sub-region is also a little more active. 4. OX
tO~ - -
(a)
3.0>~ I 0 '
i
~. ON 10' 0.0 -- 1,0)t:10
1400
I
I
1500
IgO0
I
I
I
I
1700
1800
1900
2000
Year
(b)
I
1,100
15100
,,I,JiF,,, lllll I 1600
I 1700 Year
tSO0
,nllil,,li,i 1900
2000
Figure 4 The strain releasing curve and the M-t plot in Southeast China seashore sub-region (a) T h e strain r e l e a s i n g c u r v e f r o m 1400 to 1730; ( b ) M - t Plot f r o m 1400 to 2 0 0 0
In Northwest China, the historical seismic data betbre 1900 is seriously insufficient. Considering the influence of the Haiyuan great earthquake in 1920, we regard the starting time as 1800 and its result is showed in Figure 5b. In addition, in order to validate the rationality of choosing 1800 as the starting time, we have also chose 1500 as the starting time and its result is in Figure 5a. In Figure 5a, we can see that the period from 1500 to 1750 is a placid-active cycle, which is quite different from the cycle from 1750 to 2000. This difference maybe account for that in the first cycle the strain had not been released completely, which can explain the unreasonable result of the deficient data and can prove the starting time selection in Figure 5b reasonable. That is to say the result in Figure 5b is correct. The active period of Northwest China has been nearly over, and now the strain is accumulating. In Northwest China, /'=1.33xl07 J~/2/a, which is equal to occur 1.68 earthquakes with Ms=6 every year. The seismicity of this sub-region is more active than that of North China and Southeast China seashore.
No.6
MA Hong-sheng. et al: SEISM1CITY RESEARCH IN SUB-REGIONS
601
In Xinjiang sub-region, the historical seismic data since 1900 is sufficient. Considering the influence of strong earthquakes in 1812 and 1902, we regard the starting time as 1890, and its result is in Figure 6a. In Xinjiang sub-region, earthquakes occur frequently and the strain has been accumulated to a high degree at present. In future, the possibility of strain releasing swiftly is rather high. In Xinjiang sub-region, ~=2.61×107 JI/2/a, which is equal to occur 3.29 earthquakes with Ms=6 every year. The seismicity of Xinjiang sub-region is rather more active. 2. OX 10'J -
(a)
I. 6X 10~ I. 2 X 109 '~_
8. OX 106
,~, 4. OXIO~ 0.0
-- 4. OX 108 500
1"6×109 F I. 2 ~
I
I
1600
1700
Year
I
I
I
1800
1900
2000
(b)
I0~ -
1800
1840
~880
Year
1920
1960
2000
(e)
1400
1500
lli [II
16~00
17100
Year
I
1800
fl
,ll/is
1900
- -1
2000
Figure 5 The strain releasing curve and the M-t plot in Northwest China sub-region (a) The strain releasing curve from 1500 to 2000; (b) The strain releasing curve from1800 to 2000: (c) M-t plot from 1400 to 2000
In Tibet sub-region, considering the influence of strong earthquake Ms=8 in 1833, we regard the starting time as 1900 and its result is in Figure 7. In Tibet sub-region, the active period was over in 1950. At present, the strain is accumulating. In Tibet sub-region, ~=3.34×107 J~/2/a, which is equal to occur 4.2 earthquakes with Ms=6 every year. The seismicity of Tibet sub-region is the most active one in Chinese mainland. In Chuan-Dian sub-region, we regard two different starting times as 1630 and 1900. Then we get the results in Figure 8a and b. It can be seen that the historical seismic data is insufficient and earthquakes after 1920 occur densely and fast. The loss comes to being that the strain has been released cosmically in recent fifty years. In Figure 8b, the climactic phase of strain releasing has passed now. The total strain is in a low phase and just accumulating. But, earthquakes occur actively even in the accumulating phase, in Chuan-Dian sub-region, ~=2.69x107 J~/2/a, which is equal to occur 3.4 earthquakes with Ms=6 every year. From the above results, we can get the following conclusions: The tectonic activity of Tibet sub-region is the most active in Chinese mainland. Earthquakes
602
ACTA SEISMOLOGICA SINICA
Vol. 15
2.OXI0m (a~
.-.E o'~
O.0
~
2.0)<10 a
1
1,0~i0 ~
1900 8.0X
108[ .--
1920
1940
1960
Year
1980
2000
(b')
6.O×I0"~:. t. o× ,o,I-
/
o:,oO: 1860
I ,
,
,
1880
1900
1920
1940
Year
1960
1980
2000
tc)
:l I
1750
Figure 6
L
~
1800
/
!850
I
Year
Jklhllild,llli, ihLk t
I
I 00
I
1950
I
2000
The strain releasing curve and the M-t plot in Xinjiang sub-region
(a) The strain releasing from 1860 to 2000; (b) The strain releasing from 1890 to 2000: (c) M-t plot from 1750 to 2000
8.0Y
l&
4.0)< I01 r, ,7,
0. C -
4,0YlO ~
-
8. 0>~ 10 1900
I
I
1920
5,
1840
Figure 7
1880
I
I
1940
I
Year
19'20 Year
I
1960
t
I
I
I
1980
I
2000
lIIltliJIIIl
19'~o
'
20'00
The strain releasing curve and the M-t plot of Tibet sub-region
occur rather frequently and the strain accumulates promptly. The seismicity level o f Tibet sub-region is the most active one. The second active one is the Chuan-Dian sub-region. The tec-
No.6
MA Hong-sheng, et al: S E I S M I C I T Y R E S E A R C H IN S U B - R E G I O N S
603
tonic activity of Chuan-Dian subarea is quite active. The third active one is the Xinjiang sub-region. The tectonic activity of Xinjiang sub-region is as well active and earthquakes occur frequently. The tectonic movement of Northwest China is just ordinary, but there are more earthquakes with Ms=6 at present. The tectonic activity of North China and Southeast China sub-region is weak. Especially, the seismicity of Southeast China is rather low at present. Comparing the strain accumulating and releasing curve of Tibet sub-region with that of Chuan-Dian sub-region, we find that the strain of Tibet sub-region is in the stage of accumulating and the strain of Chuan-Dian sub-region is in the stage of the remnant releasing. Comparing the strain accumulating and releasing curve of south China seashore sub-region with those of North China sub-region, we find that the strain of South China seashore sub-region is in the ending stage of releasing, and the strain of North China sub-region is probably in the final stage of releasing. In North China sub-region, there may be another middle strong earthquake process in future. The strain of Northwest China sub-region has been released on large scale, and now it is in the stage of accumulating. The strain of Xinjiang sub-region has been accumulating to a quite high stage. In future, there may occur some strong earthquakes, so we must give sufficient attention. 1.6xio' F- (~) 1.2X 109 r
8. o×,o' I-
4o×,081--
8o?,7,
1650
6. O× 108 F
,
,
1700
1750
,
,
1800 YearIS50
,
,
,
1900
1950
2000
(b)
,/'-
"
h
0.0~Z ''~ -2.0×1081
I 1900
I 1920
I
r
I
1940 Year
I 1960
I
I 1980
I
I 2000
(c)
i! I,rtJbl+llr,I,+rlixJfl/!!iJi 7
1500
I
1600
17~o 0
~
Year
' 1800
] 9LO0
I " 2000 1--
Figure 8 The strain releasingcurve and the M-t plot of Chuan-Dian sub-region (a) The strain releasing from 1630 to 2000; (b) The strain releasing from 1900 to 2000; (c) M-t plot from 1500 to 2000
4 Discussion and conclusions In our research, we pay much more attention to analyses of the earthquake placid-active phenomena in different sub-regions using the strain accumulating and releasing model, and dis-
604
ACTA SEISMOLOGICAS1NICA
Vol.15
cuss the seismicity changes of each sub-region in Chinese mainland. When we use the strain accumulating and releasing model, we have to consider the difference on the seismic data of different area and stage. In the model, we make the earthquakes of different stage and different magnitude in one sub-region convert to a uniform measure of strain. According to the net effect of the accumulated and released strain, namely the tectonic strain ascending and descending of the sub-region, we can judge the stage of placidity and activity, which reduces some of the subjectivity in the research. From the above result, we can say the model possesses a certain practical value. The average velocity of the strain accumulating ~" can determine the average seismicity level of a block. But, to make sure the stage of the seismicity at present, we must know how about the strain release. For several placid and active alternant seismicity cycles, the accumulated and released strain should be equal as a whole. In a block, if the released strain is much less than the accumulated strain, there would be some excessive and strong earthquakes to eliminate this departure in future~ and there is no other parameter with this function. In this research, we have divided Chinese mainland into several sub-regions in seismicity, which is based on the hypothesis of the active crustal blocks, thus the rationality of the division can endure oppugning. In addition, we point out that the model application premise is that we assume the accumulated and released strain is equal as a whole in an independent and complete system with one or several seismicity cycles. But in the practice, we pay attention to the following problems: l) The influence of choosing the starting time to the strain accumulating and releasing curve. In Figure 3a, the released strain level of the third active cycle is higher than that of the fourth active cycle in the North China sub-region, i.e., the activity of the third active stage is strong and the activity of the fourth active stage is weak. The earthquake activity also proves this point (JIANG, MA, 1985). But in Figure 3b, the released strain level of the fourth active cycle is higher than that of the third active cycle, and the strain level is still high up to now. This is not consistent in the real-life seismic activity. We take this instance for not considering the strain accumulating process at the starting time of the third active cycle. In this stage the strain accumulating is far faster than the releasing, so we get the result that the annual average velocity of the strain releasing is faster than that of the real-life strain releasing, which makes the strain of the sub-region have a system deviation against the real-life strain, and the strain ascend by the time passing. Thus, when we choose the starting time, we have to consider the consumed time of the strain accumulating, or else we will get the faster strain rate. To get a further research, we compare Figure 6a with Figure 6b. in Figure 6a, there is an ascending trend after the Ms=8.3 earthquake in 1902; but in the Figure 6b, there is a steady trend after the Ms=8.3 earthquake in 1902. So we think the influence of the Ms=8.3 earthquake in 1902 is very huge, and when we calculate the strain accumulating velocity, we must take it into account. Its prophase is the phase of strain accumulating, and because of the deficit of data, we cannot easily make sure the starting time. In our research we choose different starting time to calculate. Because there is a strong earthquake cycle of about one hundred years in Xinjiang sub-region, it is reasonable that we take 1890 as the starting time. On the contrary, if we take the starting time as 1860, as Figure 6b, for the strain accumulating velocity being too slow, the strain level we get is in a low phase, which is different from the real situation. Therefore, choosing the starting time is the key of using this model. When choosing, we need consider not only the integrity of the data, but also the consumed time of the strain accumulating. 2) The change influence of the strain releasing rate on the strain accumulating and releasing
No.6
MA Hong-sheng, et al: SEISMICITY RESEARCH IN SUB-REGIONS
605
curve. In the real-life earthquake catalog, there is the problem that the historic earthquakes are absent or the historic earthquakes magnitude marked higher. To solve this problem, we choose North China sub-region to do an experiment. We get a result by changing the strain releasing rate as Figure 9a. When all the terms unaltered and only reducing the strain releasing rate, we find the shape of the curve is changeless, but the total trend changes to descend. When increasing the strain releasing rate, as Figure 9b, we find the shape of the curve is also changeless, but the total trend changes to ascend.
g. O × IOs
(a)
10~1
4. O /
0.0 ._.E --4.0xlO
s
- - 8 . OX 108
-
-
[. 2 X lff
1400
t
t
I
I
I
I
1500
lG00
1700
1800
1900
2000
1500
1600
1700 Year
1800
]. 6 X 109
(b)
1.2× 109 8 . 0 × 10s-t
~
~
4.0× l0 B 0.0 1400
I
I
I
1900
I
2000
Figure 9 The experiment result by changing the strain releasing rate (a) Reducing strain releasing rate; (b) Increasing strain releasing rate
References Benioff H 195 I. Earthquakes and rock creep [J]. Bull Seism Sac Amer. 4 Ii 31-62. Gutenberg B, Richter C F 1956, Earthquake magnitude, intensity, energy and acceleration (second paper) [J]. Bull Seismol Soc Amer, 46: 1054145. HUANG Zhong-xian, CHEN Hong 1996. The seismicity changes with time in Chinese mainland and its relationship with tectonic movement [J]. Earthquake Research in China, 12(4): 403~410 (in Chinese). HUANG Wei-qiong, LI Wen-xiang, CAP Xue-feng 1994. Research on completeness of earthquake data in the Chinese mainland (II) The regional distribution of the beginning years of basically complete earthquake data [J]. Acta Seismologica Sinica, 7(4): 529~538 JIANG Ming, MA Zong-jin. 1985. The comparison between the third active cycle and the fourth active cycle in the North China sub-region [J]. Earthquake, (6): 5~11 (in Chinese). Kanamori H. 1977 The energy release in great earthquakes [J] ] Geophys Res, 82:2 981 ~2 987 QIU Jing-nan, GAP Xu 1986 The discusssion of the seismicity phases of the Chinese mainland [J]. Earthquake, (6): 41~47 (in Chinese)• SHI Zhen-liang, HUAN Wen-lin, CAP Xin-ling, et al 1974. Some characters of the seismicity in Chinese mainland[J] Chinese Journal of Geophysics, 17(I ): I~13 (in Chinese)• XIA Hao-mmg 1987. The character and the meaning of the seismicity phases division with Ms>4 in North China sub-region [J]. Chinese Journal of Geophysics, 30(3): 281 ~291 (in Chinese).
606
ACTA SEISMOLOGICA SINICA
Vol. 15
ZHANG Guo-min, GENG Lu-ming, SHI Yao-lin. 1993. The research of the strong earthquake active periods of Chinese mainland by computer model [J]. Earthquake Research in China, 9(1): 20-32 ZHANG Guo-min, GENG Lu-ming, ZHANG Yong-xian, et al. 1995. The grouping seismogenic model of tectonic blocks and the analyses of some precursor characters [J]. Acta Seismologica Sinica, 8( I ):1 ~10 (in Chinese). ZHANG Guo-min, LI Li. 1997. The research of the interaction influence of strong earthquakes grouping seismogene and grouping occurrence [J]. Earthquake, 17(3): 221~231 (in Chinese). ZHANG Guo-min, ZHANG Pei-zhen. 2000. Academic progress on the mechanism and forecast for continental strong earthquake in the first two years [J] China Basic Science, (10): 4-10 (in Chinese).
