Seismic characteristics near the epicenter of the 1303 Hongtong M=8 earthquake, Shanxi Province and its implication

In this paper, we calculated the seismic pattern of instrumental recorded small and moderate earthquakes near the epicenter of the 1303 Hongtong M=8 earthquake, Shanxi Province. According to the spatial distribution of small and moderate earthquakes, 6 seismic dense zones are delineated. Temporal distribution of ML≥2 earthquakes since 1970 in each seismic dense zone has been analyzed. Based on temporal distribution characteristics and historical earthquake activity, three types of seismicities are proposed. The relationship between seismic types and crustal medium is analyzed. The mechanism of three types is discussed. Finity of strong earthquake recurrence is proposed. Seismic hazard in mid-long term and diversity of earthquake disaster in Shanxi seismic belt are discussed.     

Spatial damage distribution of August 16, 2003, Inner Mongolia, China, M S=5.9 earthquake and analysis

The spatial damage distribution of August 16, 2003, Inner Mongolia, China, M _S=5.9 earthquake is summarized through field investigation. The moment tensor solution and focal mechanism are inverted using the digital long-period waveform records of China Digital Seismograph Network (CDSN). The relation between the spatial damage distribution and focal mechanism is analyzed according to the focal mechanism, the aftershock distribution and the spatial damage distribution. The possible relation between the characteristics of ground motion and the tectonic background of the source region is discussed in terms of the global ground motion records, historical earthquake documents and the damage distribution. Investigation reveals that the meizoseismal region is in east-west direction, which is consistent with the nodal plane of focal mechanism inversion. The meizoseismal area is relatively large and the damage of single-story adobe houses or masonry houses is more severe. This may have relations with local seismotectonic environment. Foundation item: The Special Funds for Major State Basic Research Project (2002CB412706). Contribution No. 05FE3009, Institute of Geophysics, China Earthquake Administration.     

Observation and analysis of geomagnetic abnormity associated with the Ms=5.7 Jiujiang-Ruichang earthquake

A three-component geomagnetic survey was carried out during the period from 2002 to 2004 in China including Jiujiang-Ruichang region. Comparing the ＂2005.0 surface spline model of China geomagnetic field＂ created on the basis of the survey data with the ＂1970.0 surface spline model of China geomagnetic field＂, we can see an obvious abnormity in the geomagnetic horizontal component within a range of about 100 km around the epicenter of the Ms=5.7 Jiujiang-Ruichang earthquake occurred on November 26, 2005. After the earthquake, we carded out a repeated geomagnetic survey at 21 stations in the Jiujiang-Ruichang region and created a corresponding ＂2005.0 partially revised surface spline model of China geomagnetic field＂. By comparing the above three models, analyzing the geomagnetic horizontal component at the profile in the Jiujiang-Ruichang region and quantitatively studying the geomagnetic data of every stations around the Ms=5.7 earthquake, we have obtained the geomagnetic abnormity associated with this earthquake. Then the geomagnetic abnormity and its relation with seismic activity are discussed in this paper.     

Earthquake probabilities and magnitude distribution ( M ≥6.7) along the Haiyuan fault, northwestern China

In recent years, some researchers have studied the paleoearthquake along the Haiyuan fault and revealed a lot of paleoearthquake events. All available information allows more reliable analysis of earthquake recurrence interval and earthquake rupture patterns along the Haiyuan fault. Based on this paleoseismological information, the recurrence probability and magnitude distribution for M≥6.7 earthquakes in future 100 years along the Haiyuan fault can be obtained through weighted computation by using Poisson and Brownian passage time models and considering different rupture patterns. The result shows that the recurrence probability of M _S≥6.7 earthquakes is about 0.035 in future 100 years along the Haiyuan fault. Foundation item: Joint Seismological Science Foundation of China (103034) and Major Research “Research on Assessment of Seismic Safety” from China Earthquake Administration during the tenth Five-year Plan.     

The November 14, 2001 west of Kunlun Mountain Pass earthquake: An earthquake with unsaturated surface wave magnitude

Introduction According to the Rapid Earthquake Information Release of CNDSN (Department of Earth- quake Monitoring and Prediction, China Earthquake Administration, 2002), an earthquake with surface wave magnitude MS=8.1 shook west of Kunlun Mountain Pass (KMP) at the juncture of Xinjiang, Qinghai and Xizang on November 14, 2001. This is the largest and the only MS>8.0 earthquake in Chinese mainland over 50 years since the August 15, 1950 MS=8.6 (MW=8.6) Chayuearthquake in Tibeta…     

Stochastic spatial analysis of earthquake sequence

In this paper, by means of the statistical analysis method of stochastic spatial point process, statistical analysis of spatial distribution of earthquakes in the large northern region of China is made. Emphasis is on the test and analysis of the complete spatial randomness, correlation of earthquake distribution in the different magnitude interval and random labeling. It is shown by the analysis that the spatial distribution of earthquakes in the large northern region is “clustered”, the distributions of earthquakes in different magnitude interval are positively correlated and can be modeled by a two-dimensional process. The results obtained in the paper can be used for the establishment of a reasonable spatial distribution model and have some application in the reasonable estimation of seismic hazard. The Chinese version of this paper appeared in the Chinese edition ofActa Seismologica Sinica,15, 129–135, 1993.     

The GIS and analysis of earthquake damage distribution of the 1303 Hongtong <Emphasis Type="Italic">M</Emphasis>=8 earthquake

The geography information system of the 1303 Hongton M=8 earthquake has been established. Using the spatial analysis function of GIS, the spatial distribution characteristics of damage and isoseismal of the earthquake are studies. By comparing with the standard earthquake intensity attenuation relationship, the abnormal damage distribution of the earthquake is found, so the relationship of the abnormal distribution with tectonics, site condition and basin are analyzed. In this paper, the influence on the ground motion generated by earthquake source and the underground structures near source also are studied. The influence on seismic zonation, anti-earthquake design, earthquake prediction and earthquake emergency responding produced by the abnormal density distribution are discussed.     

Ionospheric Ne disturbances before 2007 Pu’er,Yunnan, China,earthquake

Selecting three half orbits near the epicenter of Pu’er earthquake, we analyzed the Ne data recorded in their revis-ited orbits during a year before this earthquake, and extracted Ne precursors. The results show that: ① There are significant seasonal variations of ionospheric Ne in night time, which exhibit different shapes respectively in four seasons; ② There are three main shapes of Ne: single-peak, saddle-shaped and even-shaped, all of which may oc-cur in four seasons, but each season with its typical shape relatively; ③ Spatial images of Ne showed high values near the epicenter in 30 days before the earthquake, and there is a good correlation between anomaly and distribu-tion of earthquake in space and time, which reflects that these spatial anomalies were indeed concerned with the earthquake; ④There shows a certain similarity of the Ne curves among revisited orbits, which can provide back-ground information for distinguishing and identification of seismic anomaly.     

The December 26, 2004, off the west coast of northern Sumatra, Indonesia, M W=9.0, earthquake and the critical-point-like model of earthquake preparation

Long-term seismic activity prior to the December 26, 2004, off the west coast of northern Sumatra, Indonesia, M _W=9.0 earthquake was investigated using the Harvard CMT catalogue. It is observed that before this great earthquake, there exists an accelerating moment release (AMR) process with the temporal scale of a quarter century and the spatial scale of 1 500 km. Within this spatial range, the M _W=9.0 event falls into the piece-wise power-law-like frequency-magnitude distribution. Therefore, in the perspective of the critical-point-like model of earthquake preparation, the failure to forecast/predict the approaching and/or the size of this earthquake is not due to the physically intrinsic unpredictability of earthquakes. Foundation item: Ministry of Science and Technology Project (2004CB418406). Contribution No. 05FE3010, Institute of Geophysics, China Earthquake Administration.     

Surface rupture zone of the 1303 Hongtong M=8 earthquake, Shanxi Province

Based on the latest displacement of Huoshan piedmont fault, Mianshan west-side fault and Taigu fault obtained from the beginning of 1990‘s up to the present, the characteristics of distribution and displacement of surface rupture zone of the 1303 Hongtong M = 8 earthquake, Shanxi Province are synthesized and discussed in the paper. If Taigu fault, Mianshan west-side fault and Huoshan piedmont fault were contemporarily active during the 1303 Hongtong M = 8 earthquake, the surface rupture zone would be 160 km long and could be divided into 3 segments, that is, the 50-km-long Huoshan piedmont fault segment, 35-km-long Mianshan west-side fault segment and 70-km-long Taigu fault segment, respectively. Among them, there exist 4 km and 8 km step regions. The surface rupture zone exhibits right-lateral features. The displacements of northern and central segments are respectively 6～7 m and the southern segment has the maximum displacement of 10 m. The single basin-boundary fault of Shanxi fault-depression system usually corresponds to M ≈ 7 earthquake, while this great earthquake (M = 8) broke through the obstacle between two basins. It shows that the surface rupture scale of great earthquake is changeable.     

Application of apparent stress in earthquake prediction

On the basis of the assumption that ω2 model accords with source displacement spectra of moderate-small shocks, we calculate the apparent stress values of 1 020 moderate-small shocks recorded by the Digital Seismic Network of Yunnan Province by using the low-frequency flat level and corner frequencies. The results show that the apparent stress is of good significance in earthquake prediction. The moderate-small shock with apparent stress larger than 0.9 MPa can be used as a referential index to predict moderate-strong earthquakes in Yunnan area. And its relevant predictability evaluation (R value) has a high confidence level.     

Application of scaling-rule theory in crustal rock fracture to studying characteristics of seismological precursors associated with M=6.1 Shandan-Minle earthquake

In the paper, we introduce Allegre＇s scaling-rule theory of rock fracture and the probability to develop a method for predicting earthquake occurrence time on its basis. As an example, we study the characteristics of seismological precursors （seismic spatial correlation length and coda Qc） associated with the earthquake （M=6.1） occurred in Shandan-Minle, Gansu Province. The results show an increasing trend of seismic spatial correlation length and coda Qc before the earthquake. And a power exponent relation is used to fit the increasing variation form of these two parameters. The study has provided a basis for creating a method and finding indexes to predict the earthquake occurrence time by using the monitored seismic spatial correlation length and coda Qc.     

The middle-long term prediction of the February 3, 1996 Lijiang earthquake (MS=7) by the "criterion of activity in quiescence"

IntroductionIn the book Future CataS~ologr published in 1992, we proposed a viewpoiflt on using the"criterion of activity in quiescence" to predict big eathquake (MsZ7) (GUO, et al, 1992), and predicted in the book that in futore several years or in ten years a big earthquake (Ms27) will be possible to occur in the Zhongdian and nearby in Yunnan Province. In the 1994 nation-wide earthquake tendency consultation meeting we pointed out, once more, in the Zhongdian region of Yunnan Province…     

The GIS and analysis of earthquake damage distribution of the 1303 Hongtong M=8 earthquake

Introduction The 1303 Hongtong earthquake is an important earthquake in the eastern China. There is a lot of information in historical documents about the earthquake and many traces destroyed by the earthquake in the southern Shanxi Province. Many scholars have studied the earthquake from dif-ferent aspects, but mainly limited the definitions of the isoseismal and three factors of the earth-quake. Owing to being limited by the analysis technique, many useful damage information of the earthqu…     

Study on the earthquake fault of the Lulong M L=6.2 earthquake by precise relocation of aftershock

We have selected 171 near-field records from 391 aftershock records of the Lulong, Hebei Province, earthquake in October 1982 and relocated the hypocenter of 45 aftershocks using the program Hypoinverse. The distribution of aftershocks reveals a set of earthquake faults: a WNW stretching fault truncates two NNE stretching faults. The two branches of faults show the conjugate structure which is often seen in brittle fracture. The NNE stretching faults are connected together. The Luanhe river valley near Lulong developed to a rudiment rift basin surrounded by a series of faults. The fault of Lulong earthquake is a strike-slip fault with tension component. This fault type matches with the activity of Zhangjiakou-Bohai seismic belt (Zhang-Bo belt) and also shows the action of Zhang-Bo belt as a boundary of two secondary active blocks that truncates the NNE fault. Foundation item: National Natural Science Foundation of China (40234038). Contribution No. 05FE3016, Institute of Geophysics, China Earthquake Administration.     

Application of Brownian model in the northwestern Beijing, China

The mathematic theory of Brownian passage-time model and its difference from other recurrence models such as Poisson, lognormal, gamma and Weibull, were introduced. We assessed and analyzed the earthquake probabilities of the major faults with the elapsed time much greater than the recurrence interval in the northwest region of Beijing (China) in 100-year by using both Brownian passage-time model and Poisson model, and concluded that the calculated results obtained from Brownian passage-time model is more reasonable. Foundation item: Joint Seismological Science Foundation of China (103034) and Key Project “Assessment of Seismic Safety” from China Earthquake Administration during the tenth Five-year Plan.     

Estimating the size of an earthquake using short-period seismograms of the first three seconds: A simulated experiment using the 1999 Chi-Chi earthquake sequence

Most of the present earthquake early warning systems are based on broadband or strong motion recordings. How-ever, the short-period instruments are still deployed. It is well-known that short-period recordings have saturation problems for large earthquakes when estimating the size of an earthquake. Thus, it is necessary to make clear the magnitude at which saturation starts to occur for the commonly used τc and Pd measurements, respectively. To investigate the possibility of using short-period seismic recordings for earthquake early warning, we conducted a simulated experiment using the strong motion data of the 1999 Chi-Chi earthquake sequence including its main shock and 31 aftershocks, with magnitude span from 4 to 7.6. The strong motion acceleration recordings were convolved with the instrument response of short-period seismographs in northern China to simulate short-period seismograms. Parameters τc and Pd from the first-three-second seismograms were calculated for the simulated short-period recordings and compared with that obtained by the original strong ground motion recordings. The result showed that to some extent, short-period recordings can be used for threshold earthquake early warning, while the magnitude saturation of Pd estimation can be up to 6.5, better than τc estimation.     

Study on rupture zone of the M =8.1 Kunlun Mountain earthquake using fault-zone trapped waves

The observation of the fault-zone trapped waves was conducted using a seismic line with dense receivers across surface rupture zone of the M=8.1 Kunlun Mountain earthquake. The fault zone trapped waves were separated from seismograms by numerical filtering and spectral analyzing. The results show that: a) Both explosion and earthquake sources can excite fault-zone trapped waves, as long as they locate in or near the fault zone; b) Most energy of the fault-zone trapped waves concentrates in the fault zone and the amplitudes strongly decay with the distance from observation point to the fault zone; c) Dominant frequencies of the fault-zone trapped waves are related to the width of the fault zone and the velocity of the media in it. The wider the fault zone or the lower the velocity is, the lower the dominant frequencies are; d) For fault zone trapped waves, there exist dispersions; e) Based on the fault zone trapped waves observed in Kunlun Mountain Pass region, the width of the rupture plane is deduced to be about 300 m and is greater than that on the surface. Foundation item: Joint Earthquake Science Foundation of China (201001). Contribution No. RCEG200305, Research Center of Exploration Geophysics, China Earthquake Administration.     

Magnitude and distance distribution of strong aftershocks in Sichuan-Yunnan region

Using the earthquake sequences data with MS≥6.5 since 1966 in Sichuan-Yunnan region, we research the charac-teristic of the magnitude difference distribution between main shocks and their strong aftershocks; and then study the spatial distribution characteristic of the strong aftershocks away from their main shocks. The result shows that the magnitude difference distribution obeys intercepted exponential distribution, while the spatial distribution of strong aftershocks obeys normal distribution and the dominated distribution area of strong shocks is 10~39 km away from main shock. Finally the probability density function of the magnitude difference distribution and the spatial distribution of strong aftershocks is deduced.     

Gravity evolution and earthquake activities of the northeastern edge of Qinghai-Xizang block

The relationship between temporal-spatial evolution of gravity and earthquake activity during 1992–2001 has been analyzed systematically by integrally adjusting the gravity observation data of the northeastern edge of Qinghai-Xizang (Qingzang) block. The result shows that the gravity observation data of the northeastern edge of Qingzang block obtained by using the uniform starting datum can completely reflect the precursory gravity information appearing during the seismogenic process. In the genesis stage of an earthquake, regional gravity anomaly appears in a large area, resulting in related local gravity anomaly. The dynamic image of gravity field can clearly reflect the orderly evolution and earthquake activity. Foundation item: Key Project of China Earthquake Administration during the tenth Five-year Plan (100501-05-05).