Table of Content

09 March 2006, Volume 28 Issue 1

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Brief Report

DOES THE SUGGESTIVELY BURIED TAOYUAN FAULT IN CHANGDE REGION, HUNAN PROVINCE, REALLY EXIST?

HAN Zhu-jun, NIE Xiao-dong, ZHOU Ben-gang, MA Wen-tao, XIANG Hong-fa, CHEN Guo-guang

2006, 28(1):  1-11. 

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Geological, geomorphic and geophysical methods, including drilling and chronological dating, are applied to determine whether the suggestively buried Taoyuan fault exists. Stratum units at two sides of the fault are continuous. The “normal fault”, found at east side of Yuanjiang River, Yaohe town, is actually a fissure caused by un-loading. Weak cementation of the Eogene breccia is also favorable to formation of the extensive fissure. One meter of offset along the fissure is not the result of tectonic movement, but comes from up-plate falling under the gravitational action. Quaternary thicknesses at the two sides of Yuanjiang River show no abrupt change, but a normal sedimentation. According to the geomorphic feature and the fault location, suggested by previous work, three lines of shallow seismic survey are arranged at the two sides of Yuanjiang River. The sections of shallow seismic survey show that boundaries at different layers are clear and can be pursued continuously. There are no evidences to demonstrate that the suggestively buried Taoyuan fault may exist. Two drilling bores are arranged at Xunyangping Quaternary-covered area and they are located at two sides, 20m away from the suggestively buried fault. The drilling results show that the Quaternary layers are crossed almost at the same depths and the lower basal rocks are revealed, which are red clay-sand rocks of the Eogene. Thermoluminescence dating samples are collected respectively at depths of 4.5m, 9.8m and 16.8m. The experiment results are (2.2±1.8)×10⁴a, (2.9±2.5)×10⁴a and (13.1±11.0)×10⁴a, which shows that the Quaternary strata, formed at the end of mid-Pleistocene, are continuous at two sides of the suggestively buried fault. There is no neo-activity. In conclusion, there is no evidence to support the existence of the suggested Taoyuan fault. The Taiyangshan fault zone, on which the 1631 M6³/₄ earthquake occurred, is bounded at the north of Changde-Yeyang-Changsha fault zone. It provides a reasonable geological background for division of seismic belts and potential seismic sources and is also important for better understanding of structural conditions of the 1631, M6³/₄ Changde, Hunan, earthquake.

THE DISCUSSION ON SOME PROBLEMS OF THE M_s7.5 TUOSUOHU LAKE EARTHQUAKE IN 1937

LI Chen-xia, DAI Hua-guang, CHEN Yong-ming, XU Xi-wei, DAI Wei

2006, 28(1):  12-21. 

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The East Kunlun active fault zone, which lies in the valley of the Kunlun Mountains above the elevation of 4,000 meters, is an important active fault in the Northeast Tibetan Plateau. The Tuosuohu Lake earthquake of magnitude 7.5 in 1937 occurred in the eastern segment of the East Kunlun active fault zone. Four field investigations have been launched on this seism in 1963,1971 and between 1986 and 1990 respectively, and four different conclusions have been gained. From the length aspect of the surface deformation zone of this earthquake, it is commonly recognized that its east end lies in the west side of the main Ridge of Animaqing Mountains; the opinion about the west end and the location of the macro-epicenter is different. Based on our investigation and comprehensive study, a series scientific problems like geometric and kinetic characteristics, the length of the rupture zone, the maximum sinistrally horizontal displacement and the macro-epicenter were reestimated. It is considered that the total length of this zone should be at least 240km; the maximum sinistrally horizontal displacement is 8m, the maximum vertical displacement is 3.5m; the macro-epicenter is in Sanchakou.

SOME ANALYSES ON EFFECTS OF SITE CLASSIFICATION ON GROUND MOTION CHARACTERISTICS IN CHI-CHI, TAIWAN EARTHQUAKE

DONG Di, ZHOU Xi-yuan, XU Guo-dong, JI Jin-bao

2006, 28(1):  22-36. 

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According to the epicenter distance and the site classification, the 404 groups of earthquake recordings of the main shock of Chi-Chi, Taiwan, China earthquake in 1999 are sorted out in this paper. Based on these data, we analyze the statistic features of duration, PGA, envelopes and response spectra ratio of horizontal and vertical component of the acceleration recordings. The results of analyses show that the effect of site classification on characteristics of various components in acceleration time history is obvious; furthermore, fault direction also has certain effects on the characteristics of horizontal component of ground motion acceleration. The detailed research results are: 1) the duration of horizontal component of acceleration records increases with the softening of site; 2) the direction of fault slip has some effects on PGA’s attenuation features; 3) the average envelopes of acceleration records at different distances and site class basically are single peak functions of time and the envelopes of horizontal and vertical components of ground motion are obviously different; 4) with the same epicenter distance, EW/SN response spectrum ratios tend to approximate to 1.0 as site becomes softer and period shorter. V/H response spectrum ratios in short periods (<0.1s) increase with the softening of site, however, V/H ratios within long-period range (>characteristic period) decrease with the softening of site, and the decrease of V/EW ratio speeds up relatively.

STUDY OF THE SEISMICITY OF STRONG EARTHQUAKES IN YUNNAN AREA

HUANGFU Gang, QIN Jia-zheng

2006, 28(1):  37-47. 

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Yunnan locates in the east margin of the collision zone between the Indian Plate and the Eurasian Plate in the Chinese continent, where the crustal movement is violent and the moderate-strong earthquakes are frequent. In addition, the area is featured with marked active block movement. Therefore, Yunnan is a perfect place for the research on strong earthquake activity. Through the study on the temporal and spatial distribution of the M>6.7 earthquakes and the related earthquake dynamics in Yunnan in the last century, we conclude that the four seismically active periods which are characterized by the alternative activity in the east and the west part of Yunnan possibly result from the combination of the active and quiescent periods in each of the east part and the west part. And for every 100 years, there may be a period in which strong earthquakes occur in the east and the west parts simultaneously. Besides, the seismicity of strong earthquakes in Yunnan corresponds well to the one in the peripheral region. The seismicity of the great earthquakes in the Andaman-Burma Tectonic Arc Belt indicates, to some extent, the beginning of seismically active period in Yunnan. The seismicity of strong earthquakes in east Yunnan is closely related with the one in Sichuan. The strong earthquakes in Sichuan often occur later than the ones in Yunnan. Further, in the east part of Yunnan, the three procedures including continuous occurrence of moderate-strong earthquakes, quiescent period, and the occurrence of the first strong earthquake may be the style of the beginning of the earthquake active period. The above cognition is helpful to the study of earthquake prediction, seismogenic mechanism, and the dynamics of the plate margin in Yunnan.

RESEARCH ON THE CHARACTERISTICS OF LARGE EARTHQUAKE ACTIVITY ON THE ACTIVE TICTONIC BOUNDARIES IN CHINESE MAINLAND

MA Hong-sheng, ZHANG Guo-min, LIU Jie, WANG Hui

2006, 28(1):  48-60. 

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Based on the research and the division of the active tectonic blocks and their boundaries in Chinese mainland, the feature of the large earthquake activities in the 24 boundaries between the 6 grade Ⅰactive tectonic block regions and the 22 grade Ⅱ active tectonic blocks are studied. The seismicity levels on the active tectonic block boundaries are discussed considering the large earthquake frequency and the released strain energy in unit distance and time. And then, the theoretic maximal magnitude and the recurrence period of each boundary are calculated from the G-R relation. By comparing with the actual earthquake records, it is found that the intensities of the earthquake deduced from the seismic activity parameter (a/b) in the main active boundaries in Chinese mainland are consistent with that of the nature earthquakes. Meanwhile, an inverse relation is found between the recurrence period of large earthquake and the tectonic motion rate on the boundaries. These results show that the a, b value of each boundary obtained in this paper is valuable. In addition, the present seismic activities and hazards of these boundaries are also probed into with the historical data and their elapsed time on each boundary based on the hypothesis that the large earthquakes satisfy Poisson distribution.

RELATIONSHIP BETWEEN REGIONAL SEISMIC ACTIVITY EVOLUTION AND ACTIVE BLOCK IN THE SEISMOGENIC PROCESS OF STRONG SHOCKS

CHEN Yu-wei, ZHANG Jun, YAN Su-ping, QING Mei

2006, 28(1):  61-70. 

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Through systematic analysis of the whole seismic data in the 4 first class active blocks in Chinese continent and its neighbouring regions from 1972 to 2003, we get the typical mid-term seismicity evolution patterns of strong earthquake, i.e. the moderate-size earthquakes cluster and the earthquake density and specific rate increase in the future epicenter area prior to strong earthquake. This paper uses moderate earthquake growth rate to depict the acceleration growth of moderate earthquake activity in the seismogenic process of strong shocks,and the results show that the growth rate of moderate earthquake activity density can well reflect the anomaly variation character before strong shock. Analysis of each active crustal block indicates that when the moderate earthquake growth rate of the North China block is up to 180%, a strong shock will happen in the moderate earthquake anomaly concentration zone and its adjacent regions in the coming 1～3 years;and when the moderate earthquake growth rate of the West reaches 250%,we have to be alert to the occurrence of strong shock in the moderate earthquake anomaly concentration zone and its adjacent regions. Therefore,moderate earthquake growth rate can be used as a quantitative index of medium-term earthquake prediction.

CHARACTERISTICS OF RECENT EJECTA OFTHE CHANGBAISHAN TIANCHI VOLCANO,CHINA

YANG Qing-fu, SHI Lan-bin, CHEN Xiao-de, CHEN Bo, ZHANG Yu

2006, 28(1):  71-83. 

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The Changbaishan Tianchi volcano on the border between China and North Korea (42? N,128? E) is the most dangerous one with high destructive eruption potential in China. In the research of recent eruption history of the Tianchi volcano, a set of recent ejecta were recognized through field investigation, grain size analysis and petrochemistry analysis. The new ejecta were found on the northeast side of the Tianchi Lake. It is a set of multi-layered pyroclastic deposits of 9.2m thick overlying the 1668 AD airfall deposit. Grain size analysis shows that the ejecta are composed mainly of fall deposit with an interbed of surge deposit, and the type of eruption is phreatomagmatic. Fractal dimension value of the surge deposit is 2.7113, while that of the fall deposits ranges from 2.3028 to 2.4627, having an average value of 2.36. In the microscope, skeleton vitric fragments are observed but clay mineral is not found in the deposits, indicating that they are primary deposit produced by explosive eruption. Petrochemistry analysis of pumice component indicates that the magma can be assigned to trachytic magma. Based on historical records, stratigraphic correlation and features of the deposits, it is estimated that the ejecta are the product of 1903 AD eruption.

THE APPLICATION OF REFRACTION METHOD TO SHALLOW EXPLORATION OF WESTERN ZHENGZHOU AREA

WU Yi, JIA Shi-xu, DUAN Yong-hong, XU Chao-fan, YANG Zhuo-xin

2006, 28(1):  84-92. 

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Seismic refraction method is tentatively used in the exploration of urban active faults where strong interference of surface waves exists and it is difficult to use seismic reflection survey. Original seismic refraction data are calculated and inversed by using time-terms, curve of differential time-distance and finite-difference tomography, to investigate the effect of the new technique in the exploration of urban active faults.In this paper, velocity structures and interface structures are obtained after the shallow seismic refraction data in the western segment of Xushui fault of western Zhengzhou are calculated and inversed by using the above-mentioned three calculation methods, and structural characteristics and depths of main geologic strata are got by integrating inversion results and features of seismic phases. The results of these three methods are similar, and they are confirmed by drilling data in the profile. The seismic refraction method can be used in the exploration of urban active faults.

ANALYSIS OF RELATION BETWEEN BLOWOUT OF OIL AND GAS WELL AND EARTHQUAKE

GAO Xiao-qi, ZHU Cheng-ying, GAO Guo-ying, XU Qiu-long, YANG Zhu-zhuan, CHEN Mei-hua

2006, 28(1):  93-98. 

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The new No.5 well is a petroleum well with 2260m depth, and it spewed nine times from 1978 to 2004. During a blowout, a lot of natural gas with a little of oil and oil wax were spewed together with underground water; the tiptop height of water column was more than 10m. Based on the statistics, the blowout phenomenon of well did not have obvious cycle characteristics.Based on the analysis of earthquake cases, the authors selected the earthquakes that occurred in the half year after the No.5 well had spewed to study the relation between earthquake and blowout of well. The result shows that the corresponding rate for M5 earthquake is 33.3% in the range of 100km, 0 for M5 earthquake in a range of 100km to 300km, 0 for M6 earthquake in the range of 500km, and 60% for large earthquake or strong earthquake swarm in the range of 1000km.The probable reason was explained. Finally, the authors raised their standpoint about earthquake tendency concerning the blowout of No.33 well in Wusu and the new No.5 well again in 2005.

APPLICATION OF SATELLITE THERMAL INFRARED REMOTE SENSING IN DETECTION OF VOLCANO ACTIVITY

QU Chun-yan, SHAN Xin-jian, MA Jin

2006, 28(1):  99-110. 

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The paper first summarizes the advances in detection of volcano activity using satellite thermal infrared remote sensing and discusses the feasibility and means to monitor the thermal anomaly caused by volcano activities through satellite thermal infrared remote sensing technology. Then, some applied methods are put forward to remove the influences of geological environments and meteorological variation on earth surface thermal infrared radiation for extracting volcanic thermal anomaly. These methods include getting rid of the influences of ground environment factors, such as terrain, vegetation and rock types by establishing brightness temperature variation models of volcanic region and eliminating the influences of weather by difference calculation of brightness temperature between volcanic region and adjacent contrast region. Finally, the paper gives a study case of Changbai Mountains volcano. By using NOAA AVHRR data of the three years of 1999, 2003 and 2004, the authors analyzed and interpreted the thermal infrared brightness temperature images of Changbai mountain volcano region, and calculated the annual variations of brightness temperature of Changbai Mountains Tianchi Lake and adjacent contrast region. The result shows that the spatial distribution of brightness temperature in Changbai mountains volcano area is mainly controlled by hypsography and physiognomy, and presents a “tundish” shape. From Tianchi Lake to its peripheral places, the brightness temperature increases gradually, but the Tianchi Lake is a clear hot spot in cold background. The temporal variation of brightness temperature in this region is mainly influenced by seasons and presents seasonally changeable characteristics. The comparison analyses of annual variations of brightness temperature between Tianchi Lake and contrast region reveal that the brightness temperature of Tianchi Lake in 2003 and 2004 increased markedly with a magnitude about 2K compared with that in 1999. We suppose this elevated temperature is likely to be a reflection of increasing activity of Tianchi volcano in recent years. Furthermore, this result is consistent with that obtained by Changbai Mountains Tianchi Volcano Observatory in the past 4 years. These indicate that the satellite thermal infrared remote sensing is a feasible and effective measure for detecting volcano activity, and its application in detection of volcano activity deserves more detailed research.

APPLICATION OF SPACEBORNE SYNTHETIC APERTURE RADER INTERFEROMETRY ON MORPHOTECTONIC RESERCH IN BENGCUO AREA OF TIBET

NING Shu-zheng, REN Jin-wei, SHAN Xin-jian, TAO Wei, ZHOU De-min

2006, 28(1):  111-118. 

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Using ERS-1/2 radar satellite data, we generated the Digital Elevation Model by Interferometric Synthetic Aperture Radar, and the ERS-1/2 DEM that we generated is obviously superior to the 1/25 ten thousand-scale DEM of the National Fundamental Geographic Information System of China and the 90 meter spatial resolution’s SRTM DEM that America published in 2004 when it shows the characteristics of tiny structure relief. By analyzing the relief characteristics of Bencuo fault zone based on ERS-1/2 DEM, we found that the relief on the connection location of Bengcuo and Pengcuo fault zones had complex characteristics. A structure relief that is similar to Pengcuo fault zone crossed through Dazi-Dasha fault on Bengcuo fault zone, while Dazi-Dasha fault crossed through a gully at this place. This indicated that Dazi-Dasha fault was active at this place in recent time, at the same time, Naka-Naduiduo fault severed by the gully which was cut through by Dazi-Dasha fault. Therefore, Naka-Naduiduo fault is formed earlier than Dazi-Dasha fault.

ANALYSES OF IMAGE FEATURE OF MAJOR ACTIVE FAULTS ALONG THE EASTERN MARGIN OF ALTAI MOUNTAINS

HONG Shun-ying, SHEN Xu-hui, LAI Mu-shou, CHEN Zheng-wei, JING Feng, OUYANG Xin-yan, E A Rogozhin

2006, 28(1):  119-128. 

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Using remote sensing (RS) data, the major active faults of the eastern margin of Altai Mountains——the Hovd Fault and the Har-Nuur Fault, are studied, the detailed rupture character is analyzed from a viewpoint of topographic features, and the fault geometry and kinematics characteristics are revealed. Preliminary researches indicate the scale, slip-rate and strong seismic activity of active faults along the eastern margin of Altai Mountains are not weaker than those of the southwest’s. The Hovd Fault is of NNW-direction right-lateral strike-slip, with the length of 600 km, the maximal right-lateral displacement of river system of 9km since mid-Pleistocene(Q_p²), the possible slip-rate of 3.8～12.3mm/a,and the approximate average slip-rate of 7.8mm/a; The Har-Nuur Fault is of NNW-direction right-lateral strike-slip, with the length of 480 km. The fault is obviously active since Holocene(Qh), and there are signs of the latest faulting on the alluvial fans of Quaternary. So, the intense neotectonic movement and seismic activity on the eastern margin of Altai Mountains are related to the collision of India-Eurasia plate and maybe to the regional kinematic process.

GEOMETRICAL CHARACTERISTICS OF FRACTURES AND ROCK QUALITY ASSESSMENT IN GRANITE IN THE BEISHAN AREA, GANSU PROVINCE

LI Ya-ping, XU Jian-dong, YU Hong-mei

2006, 28(1):  129-138. 

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Geometrical parameters of fractures developing in natural rocks, such as density, dominant orientations, length, fracture aperture, are long recognized by engineering scientists because they are not only important parameters to fluid dynamics of fracture systems but also main considering factors for large-scale projects during construction and stability analysis.In this thesis, as a candidate area for high level waste repository (HLW) in China, the rock mass fracture system of the Bantan unit granite of the Jiujing block in the Beishan area, Gansu province, is chosen as the study object. The fracture system is studied in detail by field bedrock outcrop fractures surveying and combining the completed regional geological survey results with acoustic borehole television measurements. Traditional probabilistic statistics and the fractal theory are used to analyze the fracture geometric parameters including fracture length, azimuth and density. Statistics and calculation using the ArcGIS software are made to study fracture distribution characteristics in the granite rock mass. Quantitative description of fracture geometrical parameters is performed in order to provide necessary basic data for the selection of HLW. In the same time, by combining fracture density with fracture network spatial structure and using fractal dimension, the quality of rock mass of the Bantan unit granite is assessed. Fractal dimensions not only describe fracture number of rock mass but also reflect homogeneous degree of fracture distribution and the intact and cracked conditions. So rock mass quality classified by fractal dimensions combined with RQD is more objective and efficient than single RQD index. Above research indicates that the fracture network is characterized by fractal distribution. Fractal dimensions of five sampling sites are in turn 1.636, 1.548, 1.596, 1.724, and 1.604, respectively, and fall into the range between 1.5 and 1.75. According to the rock mass quality classified by fractal dimensions, the Bantan unit granite belongs to rock mass with fracture well developed and normal quality.

OSL DATING OF A SANDSTONE XENOLITH IN THE VOLCANIC ROCKS OF THE NANWAN VOLCANO, WEIZHOU ISLAND, BEIBU BAY

FAN Qi-cheng, SUN Qian, WANG Xu-long, YIN Gong-ming, LONG An-ming, YIN Ke-jian

2006, 28(1):  139-141. 

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The Weizhou Island is a volcanic island in the Beibu Bay. Volcanic activity on the island can be roughly divided into two stages, mainly in the Early-Middle Pleistocene and the Late Pleistocene separately. Eruptions of the Nanwan Volcano (late stage activity of Weizhou Volcanic Province) were typical phreatomagmatic eruptions, forming a big maar and thick ring walls of pyroclastics and debris. In this paper, we reported the OSL dating result of the sandstone xenoliths, which were trapped in the two volcanic pyroclastic layers of the Nanwan Volcano. The ages revealed that the activity of the Nanwan Volcano mainly occurred in ca 30ka ago, at the end of the Late Pleistocene.

INFLUENCE OF JINGBEI GEOTHERMAL FIELD EXPLOITATION ON SUBSURFACE FLUID BEHAVIORS

LIU Cheng-long, CHE Yong-tai, LÜ Jin-bo

2006, 28(1):  142-149. 

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Much interference has been found in seismic subsurface fluid behaviors. The interference of subsurface water resource exploitation is very universal, and that of hot water exploitation is severe. It affects the observation on subsurface fluid. So, the influence of ground water exploitation on subsurface fluid behaviors should be observed, investigated and researched. Based on hydro-geological settings, exploitation history and actualities of the Jingbei geothermal field, the influences of hot water production on subsurface fluid behaviors in observation wells, which have different hydro-geological settings and different intervals from exploitation wells, are analyzed. Discrepancies of the influence on different observation items are also discussed. Our result shows that disturbance distance of hot water exploitation on subsurface fluid behaviors is within 5km in the Jingbei geothermal field, and the influence on behaviors of the observation wells nearby the water-transmitting fault is most notable. As for the effects on observation items, those on water level and temperature rank first, the escape gas (Rn, Hg) comes second, and that on soil gas (CO₂) is inconspicuous.

DATABASE OF REGIONAL SEISMOTECTONIC MAP OF SOUTHWEST CHINA

SHA Hai-jun, LÜ Yue-jun, TANG Rong-yu, PENG Yan-ju

2006, 28(1):  150-156. 

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The assessment of regional seismotectonic environment is very important for seismic safety evaluation of engineering sites, and it is essential to compile a regional seismotectonic map for the region where engineering site is. For reusing the work products of seismic safety evaluations in past years and lessening repetitive hard work, it is a valuable work to build a database of regional seismotectonic map for regions where a number of seismic safety evaluation of engineering sites have been accomplished.In the past few years, we have accomplished many projects of seismic safety evaluation of engineering sites in southwest China. Combining with the work of other groups, it is possible to build the database of regional seismotectonic map in southwest China.As a useful desktop mapping software and GIS, MapInfo provides a powerful solution for mapping geographic information. It is selected as the platform to build our database. In database design of GIS, the spatial information and attribute information are usually separated considering the large quantity of data, efficiency and convenience in analysis and query of spatial information. Separate design of spatial database and attribute database is also convenient for extension and share of database. For meeting the requirement of seismic safety evaluation code, the regional seismotectonic map must include: 1) age, type and kinetic characteristic of faults in Qh; 2) active fault segment; 3) range and sediment thickness of active basin in Qh; 4) characteristic of modern tectonic stress field; 5) the epicenter distribution of earthquakes M≥4³/₄. This decides that the database of regional seismotectonic map is composed of multiple layers, multiple basic types and multiple relational tables.The database of regional seismotectonic map of southwest China on MapInfo platform is built by using the separate design of spatial database and attribute database with the structure of multiple layers, multiple data types and multiple relational tables; and basic function of the database and output method of regional seismotectonic map is showed in the end.