The coda attenuation of the Yao'an area in Yunnan Province

2000年1月15日云南姚安发生了6．5级地震．震后围绕震中区架设了一个由6套拾震器-记录仪组成的临时数字地震台网．在所记录的余震中，有402次余震有较精确的定位．依照Sato的单散射模型分析观测的尾波短记录，获得了姚安地区地壳的尾波平均品质因子Qc(f)=49f^0.95，f=1．5～20．0Hz，具有高构造活动性区域的衰减特征．

The coda attenuation of the Yao'an area in Yunnan Province

An earthquake with M=6.5 happened on January 15, 2000 in Yaoan of Yunnan Province. After the earthquake, a temporary digital network with 6 detectors around the epicenter area was set up. 402 aftershocks were located more precisely. According to coda short recording observed, the coda averaging quality factor has been acquired via Satos single scattering model analyses, Qc( f )=49f 0.95,f=1.5~20.0 Hz, which has the attenuation characteristics of high structural active region.

Three-dimensional seismic velocity tomography of the upper crust in Tengchong volcanic area, Yunnan Province

Based on data collected by deep seismic sounding carried out in 1999, a three-dimensional P wave velocity structure is determined with tomographic inversion. The tomographic result shows that there is a P wave low velocity zone (LVZ) in the upper crust beneath the Tengchong volcanic area. The LVZ is in the depth of 7~8 km and may be a smgma chamber or a partial melting body. The result also shows that the LVZ is in the northeastern side of the Rehai hydrothermal field, which is located in another LVZ near the surface. The shallow LVZ may represent a well-developed fracture zone. The strong hydrothermal activity in Rehai area can attribute to the existence of fractures between two LVZs. These fractures are the channels for going upwards of the deep hot fluid.

Seismological study on the crustal structure of Tengchong volcanic-geothermal area

Based upon the deep seismic sounding profile conducted in the Tengchong volcanic-geothermal area, a two-dimensional crustal P velocity structure is obtained by use of the finite-difference inversion and the forward travel-time fitting method. The crustal model shows that there is a low velocity zone in upper crust in the Tengchong area, which may be related to the volcanic-geothermal activities, and two intracrustal faults (the LonglingRuili fault and Tengchong fault) exist on the profile, where the Tengchong fault may extend to the Moho discontinuity. Meanwhile, based on teleseismic data recorded by a temporary seismic network, we obtained the S-wave velocity structures beneath the RehaiRetian region in the Tengchong area, which show the low S-wave velocity anomaly in upper crust. The authors discuss the causes of Tengchong volcanic eruption based on the deep crustal structure. The crustal structure in the Tengchong volcanic-geothermal area is characterized by low P-wave and S-wave velocity, low resistivity, high heat-flow value and low Q value. The P-wave velocity in the upper mantle is also low. For this information, it can be induced that the magma in the crust is derived from the upper mantle, and the low velocity anomaly in upper crust in the Tengchong area may be related to the differentiation of magma. The Tengchong volcanoes are close to an active plate boundary and belong to plate boundary volcanoes.

An experimental study of the dynamic features of shadow areas of caustics in response to loading/unloading fracture

Using a plexiglass sample and by means of real-time holographic interferometry and shadow optical method of caustics, the different features of dynamic variation in stress (strain) field, plastic area and nucleation zone (shadow area) when the sample fractures during loading (loading-fracture) and unloading (unloading-fracture) are studied visually. The results show that the strain nuclei (zones with dense fringes) appear first at the tips of prefabricated cracks at low stress, and then the shadow areas of caustics form with the increase of load. These nuclei and shadow areas can become larger, or smaller, when the process of loading, or unloading, goes on. When the stress is kept within a certain range, the shadow areas of caustics can become larger and smaller alternatively with repeated loading and unloading (cyclic loading). However, when loading and unloading at high stress, in particular when the macrofracture is about to appear, the variations of the shadow areas of caustics are irreversible and quite different. The shadow areas of caustics expand rapidly at an increasing speed when loading-fracture appears. In contrast, the shadow areas of caustics expand at a lower speed when unloading-fracture appears; besides, there is a circular shadow in front of the sharp-angle shaped area.

Physical meaning and prediction efficiency of the load/unload response ratio of rocks in strain-weakening phase before failure

Rock experiment results indicate that the load/unload response ratio (LURR) of rocks expressed via strain energy may have singular or negative value after the stress in the rock reaches its maximum before rock failure or when the rock goes into the strain-weakening phase. The universality of this phenomenon is discussed. Expressed via strain or strain energy and the travel time of P wave, the variation form of the reciprocal of LURR during the process of rock failure preparation is derived. The results show that after a sharp decrease the reciprocal of LURR reaches its minimum when the main fracture of the rock is about to appear. This feature can be taken as an indication that the rock main fracture is impending.

Application of Commensurability in Earthquake Prediction

This article introduces application of the expanding commensurability in earthquake prediction. The results show that most of the world’s major earthquake occurred at their commensurable points of time axis. An EQ 7.0 occurred in Lushan of China on 2013-04-20 and an EQ 8.2 occurred in Iquique of northern Chile on 2014-04-01 all occurred at their commensurable points of time axis. This once again proves that the commensurability provides an important scientific basis for the prediction of major earthquakes, which will occur in the area in future.

Study on Correlation of Tidal Forces with Global Great Earthquakes

The correlation between the celestial tidal forces and earthquakes has been a controversial problem, although its research history is very long. This paper analyzes the relation between the tidal forces and all the earthquakes of magnitudes no less than 7.0 which occurred in the entire world from year 1900.0 to 2000.0 by calculating tidal forces and the run tests which yields the runs of earthquakes near the extreme and non-extreme values of the tidal forces. It is shown that the occurrence of an earthquake is relevant to the tidal forces. From the analysis of the relation between the ecliptic longitudes of the lunar ascending node and the seismic activities of the principal seismic belts and regions in the world, it is also shown that the lunar node tide is possibly one of the important astronomical contributing factors of the seismic activities there. The results enrich and support the relevant study of the relation between celestial tidal forces and earthquakes.

A GREAT OFFSET VALLEY IN JINSHA RIVER NEAR QIAOJIA,YUNNAN PROVINCE

Ⅰ. INTRODUCTION It is R. E. Wallace et al. who successfully used the concept of offset valley in measuring fault slip in the world. G. Ding et al. noticed and used the concept to study the active faults in China. An offset valley implies that a moving strike slip fault gradually offsets the geomorphological units over the fault, such as the valleys,

射电脉冲星搜寻工作的进展

评述了射电脉冲星搜寻及观测研究的巨大贡献和重要意义，分析了影响脉冲星搜寻工作的几个关键因素（如灵敏度、色散、观测频率及设备等），着重介绍和分析了自发现脉冲星（特别是发现第一颗毫秒脉冲星）以来所进行的卓有成效的脉冲星搜寻工作（包括脉冲星的早期搜寻、毫秒脉冲星的初期搜寻、高银纬脉冲星搜寻、定向搜寻以及进一步的广域深空搜寻等）的情况、结果、意义和进展。

THE LATERAL INHOMOGENEITY IN YUNNAN PROVINCE, CHINA

Images of the velocity cross--section at 10 different depths in Yunnan Province have been suc-cessfully reconstructed, using the principle and method of seismic tomography (ST). These velocitycoss-sections are consistent with the results of six velocity profiles of deep seismic sounding. The reconstruction method of ST used in this paper has two advantages: (i) The velocity modeli determined by spe cifying node--velocities of hexahedron and linear interpolation through knownbasic function. A velocity field with lateral continuous velocity value and vertical discontinuitiesis established. This model is obviously better than the block model of constant velocity. The verticaldiscontinuities allow the model to simulate velocity discontinuities in the crust and upper mantle. (ii)The velocity and hypocenter parameters are separated by introducing an orthogonal projection oper-ator. Sequential orthogonal triangularization and modified singular decomposition are adopted.These measures reduce the RAM

High-precision thermal ionization mass spectrometry dating of young volcanic rocks by using U-series method

A high precision thermal ionization mass spectrometric (HP-TIMS) technique is used to determine 238U,234U,232Th,230Th concentrations and their ratios in whole rocks and minerals separated from Ouaternary Maanshan, Dayingshan and Heikongshan volcanic rocks of Tengchong volcanic field .Yunnan Province, China. The 238U-230Th isochrons are given, yielding four age values (227 ? 20) ka (D-1, Dayingshan), (79.6 ±5.5) ka (D-7, Dayingshan), (21.9 ± 3.0) ka (h-1, Heikongshan), and (7.5 ± 1.0) ka (M-1, Maanshan). The result is not only consistent with but also preciser than those measured by the K-Ar method and the alpha spectrometry U-series method, indicating that the HP-TIMS method is reliable and has high precision. Besides, a procedure of HP-TIMS analysis of young volcanic rocks in China is set up preliminarily.

Longling-Lancang fault zone in southwest Yunnan, China——A newly-generated rupture zone in Continental crust

The Longling-Lancang fault zone, consisting of sets of en echelon or clustered faults, is a newly-generated rupture zone. it is characterized by the distribution of active faults, earthquake faults and earthguakes in zones. Formed in the Early-Middle Pleistocene, stili active in the late, it moves dextrally and extensionally. it tends to cut off the locked segments and discontinuous segments at first, then pervades totally along the zone, accompanied by strong earthguakes.

FLUIDS AT THE ACTIVE PORTIONS OF FAULTS

The major zones of seismic activity are closely related to active deep faults. Great earthquakes often occur at the intersections of several active faults, their branching, turning and at the places where further developments

Average slip-rate and recent large earthquake ruptures along the Garzê-Yushu fault

Our field investigation obtains new evidence of the later Quaternary activity and recent large earthquake ruptures of the Garzê-Yushu fault. The average left-lateral slip-rate along the fault is determined to be (12 ± 2) mm/a for the last 50000 years from both offset landforms and ages of the correlative sediments. This result is very close to the estimated average left-lateral slip-rate for the Xianshuihe fault, suggesting that the horizontal movement along the northern boundary of the Sichuan-Yunnan active tectonic block and the northeastern boundary of the Qiangtang active tectonic block has been basically harmonious during the later Quaternary period. Remains of ground ruptures of recent large earthquakes have been discovered along all 3 segments of the fault, of which, the 1896 rupture on the northwestern segment is at least 70 km long, and its corresponding earthquake could be of moment magnitude 7.3. The latest rupture on the middle segment of the fault has a length of about 180 km, and was produced by an unknown-age large earthquake that could have a moment magnitude of about 7.7. Along the southeastern segment of the fault, the latest unknown-age rupture is about 65 km long and has a maximum left-lateral coseismic displacement of 5.3 m, and its corresponding earthquake is estimated to be as large as about 7.3 of moment magnitude. Based on relevant investigation, an inference has been drawn that the later two large earthquakes probably occurred in 1854 and 1866, respectively. These demonstrate that the individual segments of the studied Garzê-Yushu fault are all able to produce large earthquakes.