Crustal Stress Evolution over the Past 700 Years in North China and Earthquake Occurrence

Fault interaction and earthquake occurrence have attracted much attention in seismological community during recent years. Many studies have shown that the rupture of one fault could encourage or discourage earthquake nucleation on a neighboring fault, depending on the relative geometry of the two faults and the earthquake rupture mechanisms. In this paper, we simulate the evolutionary process of cumulative Coulomb failure stress change （ CCFSC ） in North China since 1303, manifested by secular tectonic stress loading and occurrence of large earthquakes. Secular tectonic stress loading is averaged from crustal strain rates derived from GPS. Fault rupture parameters of historical earthquakes are estimated as follows： the earthquake rupture length and the amount of slip are derived based on their statistical relationships with the earthquake intensity distribution and magnitude, calibrated using parameters of instrumentally measured contemporary earthquakes. The earthquake rake angle is derived based on geologically determined fault orientational parameters and seismically estimated orientation of regional tectonic stresses. Assuming a layered visco-elastic medium, we calculate stress evolution resulting from secular tectonic loading and coseismic and postseismic deformation. On the eve of each large earthquake, the accumulated stress field is projected to the fault surface of that earthquake and the CCFSC is evaluated to assess the triggering effect of CCFSC. Forty-nine earthquakes with M≥6.5 have occurred in North China since 1303. Statistics shows that 39 out of the 48 subsequent events were triggered by positive CCFSC, yielding a triggering rate of 81.3%. If we use the accumulative stress field to evaluate the CCFSC for the M ≥ 5.0 earthquakes that occurred in North China since 1303, we find that 75.5% of those events were triggered. The triggering rate for the M ≥ 5.0 earthquakes after the 1976 Ninghe earthquake is up to 82.1%. The triggering rates can be higher if corrections are made for some aftershocks which were wrongly identified as occurring in stress shadow zones because of errors in parameter estimates of historical earthquakes. Our study shows a very high correlation between positive CCFSC and earthquake occurrences. Relatively high CCFSC in North China at present is concentrated around the Bohai Sea, the west segment of the Northern Qinling fault, the western end of the Zhangjiakou-Bohai Sea seismic zone, and the shiyuan basin, Shanxi graben, suggesting relatively higher earthquake potential in these areas.

Study on the Triggering Effect of the October, 2005 Pakistan M_W7.6 Earthquake on Its Aftershocks

The influences upon aftershocks of Coulomb failure stress change (CFSC) generated by the main-shock of the October 8, 2005, Pakistan earthquake are calculated and analyzed. The following factors are included in the calculation: (1) the difference between the pore fluid pressure and the medium elastic constant in the fault plane area and those of its surrounding medium; (2) the tectonic stress direction of the seismic source area; (3) the aftershock failure mechanism of aftershocks is calculated by stacking the tectonic stress with the stress change generated by the main-shock. Our study, which includes many factors, fits fairly well with the aftershock distribution. It indicates that most of the aftershocks were triggered by the Pakistan main-shock that occurred on October 8, 2005.

On the Consistency of Large Earthquake Moment and Strain Rate Inferred from GPS Data in North China

The new GPS data can map crustal strain rates over large areas with a useful degree of precision. Stable strain measurement results open the door for improved estimates of earthquake occurrence. The Kostrov’s formula (1974) translates the smoothed strain rates in North China into geodetic moment rates. In North China, the ratio of seismic moment released to moment accumulated from GPS measurement is 60.6% in NS direction, 68.9% in EW direction, and 104.1% in NE shear direction. The near unit ratio points to the reliability of GPS measurements there. The combination of historical seismicity and GPS measurement offers a powerful attack on earthquake hazard.

Co-seismic Slip Distribution of the 2001 Kokoxili Earthquake Inverted by the GPS Data

The authors analyze co_seismic displacement field derived from the Global Position System (GPS) observations collected before and after the 2001 Kokoxili earthquake, western China. Using the co_seismic displacement data, and constrained with surface rupture data, they invert co_seismic slip distribution along the seismic fault. Their result shows that the earthquake ruptured the upper crust down to a depth of 13.1～22km (at 70% certainty), with its optimal estimate at 16.5km. A 2～3m left_lateral strike slip is resolved between the Sun Lake segment and the west end of the main rupture zone, although surface rupture has not been observed there. The surface rupture of this earthquake is ended at the Sun Lake to the west, but left_lateral slip of 1.5～2.0m seems to exist beyond the east end of surface rupture observed from field geology. Seismic moment release estimated using GPS and surface rupture measurement is 6.0×10 20 N·m, which is in good agreement with the result obtained from seismic wave inversion.

浅析嵩明县农村生活垃圾治理

文章以云南省嵩明县农村生活垃圾处理现状为对象,通过调查嵩明县农村生活垃圾处理存在的问题,结合国内各地在垃圾处理方面的先进经验以及嵩明县农村生活垃圾增量趋势及处理模式、地理环境,从农村生活垃圾处理资源化、减量化、无害化的角度出发,探索了一种符合嵩明县农村生活垃圾治理需求的垃圾处理模式。

GPS-constrained inversion of present-day slip rates along major faults of the Sichuan-Yunnan region, China

A linked-fault-element model is employed to invert for contemporary slip rates along major active faults in the Sichuan-Yunnan region (96°-108°E, 21°-35°N) using the least squares method. The model is based on known fault geometry, and constrained by a GPS-derived horizontal velocity field. Our results support a model attributing the eastward extrusion of the Tibetan Plateau driven mainly by the north-northeastward indentation of the Indian plate into Tibet and the gravitational collapse of the plateau. Resisted by a relatively stable south China block, materials of the Sichuan-Yunnan region rotate clockwise around the eastern Himalayan tectonic syntaxis. During the process the Garzê-Yushu, Xianshuihe, Anninghe, Zemuhe, Daliangshan, and Xiaojiang faults, the southwest extension of the Xiaojiang fault, and the Daluo-Jinghong and Mae Chan faults constitute the northeast and east boundaries of the eastward extrusion, with their left slip rates being 0.3-14.7, 8.9-17.1, 5.1 ± 2.5, 2.8 ± 2.3, 7.1 ± 2.1, 9.4 ± 1.2, 10.1 ± 2.0, 7.3 ± 2.6, and 4.9 ± 3.0 mm/a respectively. The southwestern boundary consists of a widely distributed dextral transpressional zone other than a single fault. Right slip rates of 4.2 ± 1.3, 4.3 ± 1.1, and 8.5 ± 1.7 mm/a are detected across the Nanhua-Chuxiong-Jianshui, Wuliangshan, and Longling-Lancang faults. Crustal deformation across the Longmenshan fault is weak, with short-ening rates of 1.4 ± 1.0 and 1.6 ± 1.3 mm/a across the Baoxing-Beichuan and Beichuan-Qingchuan segments. Northwest of the Longmenshan fault lies an active deformation zone (the Longriba fault) with 5.1±1.2 mm/a right slip across. Relatively large slip rates are detected across a few faults within the Sichuan-Yunnan block: 4.4±1.3 mm/a left slip and 2.7±1.1 mm/a shortening across the Litang fault, and 2.7±2.3 mm/a right-lateral shearing and 6.7±2.3 mm/a shortening across the Yunongxi fault and its surrounding regions. In conclusion, we find that the Sichuan-Yunnan region is divided into more than a dozen active micro-blocks by a large number of faults with relatively slow slip rates. The eastward extrusion of the Tibetan Plateau is absorbed and adjusted in the region mainly by these faults, other than a small number of large strike-slip faults with fast slip rates.

Far-field coseismic displacements associated with the 2011 Tohoku-oki earthquake in Japan observed by Global Positioning System

Analysis of GEONET observations covering the entire territory of Japan shows that the great Tohoku-oki earthquake that occurred on March 11, 2011 off the east coast of Honshu in Japan caused an eastward movement of the northern part of the island by as much as 5.3 m. The GPS data from TEONET in China were used to derive far-field coseismic displacements and to assess the impact of the Tohoku-oki earthquake on crustal deformation in eastern China. The results reveal that the coseismic horizontal displacements induced by the earthquake are the level of millimeters to centimeters in North and Northeast China, with a maximum of 35 mm. Strain analysis also indicates that the earthquake resulted in an increase in the tensile strain on the north-northeast trending faults in North and Northeast China. The tensile strain imposed on the Yilan-Yitong and Dunhua-Mishan faults is more significant than that imposed on the faults in North China; the maximum normal strain reaches about 40 nano-strain. Considering that the static Coulomb stress loaded on the faults is limited, its effect on the regional seismic activity may not be significant.

Influence of the March 11,2011 M_w 9.0 Tohoku-oki earthquake on regional volcanic activities

Two days after the March 11,2011,Mw 9.0 Tohoku-oki earthquake,Shinmoedake volcano,located on the Japanese island of Honshu,erupted.Was this eruption triggered by the Tohoku-oki earthquake?Could Mount Fuji and Changbaishan volcanoes also be triggered to erupt?By calculating changes in the regional stress-strain field that resulted from the earthquake,we find that Mount Fuji,Shinmoedake and Changbaishan volcanoes are all located in regions of volumetric expansion.The volumetric expan-sions at a depth of 10 km are up to～220 nano-strain,～8 nano-strain,and～14 nano-strain,respectively,for the three volcanoes. The strain changes inferred from GPS co-seismic displacements also suggest that these three volcanoes are located in regions with surface areal expansion.Considering that the expansional stress may cause the opening of magma channels,exsolution of CO2 gases stored in magma,and a series of positive feedback effects,the Tohoku-oki earthquake may result in an increase in the activ-ity of these volcanoes.Attention should be paid to potential triggering of volcanic eruptions by stress changes induced by the Tohoku-oki earthquake.

Far-field coseismic displacements associated with the great Sumatra earthquakes of December 26,2004 and March 29,2005 constrained by Global Positioning System

Based on continuous GPS observations within China as well as global GPS tracking network, a calculation has been made of far-field coseismic displacements associated with the December, 2004 (Mw = 9.3) and March, 2005 (Mw = 8.7) earthquakes. The far-field coseismic displacements are associated with the 2004 shock range more than 6000―7000 km in both north-south and east-west dimensions, and depict an undulated wave pattern of contraction and extension. The coseismic displacements associ-ated with the 2005 event, however, are distributed near the epicentral region, and the event itself may be an aftershock of the 2004 earthquake.