德国南部地区Love波相速度分布

在利用远震面波资料研究小区域内的地壳上地幔速度结构时，传统的面波层析成象所依据的大圆路径和平面波入射假设不能成立．本文利用德国区域地震台网记录的Love波资料，根据Friederich和Wielandt提出的面波波场和速度结构联合反演方法，对德国南部地区的Love波相速度横向不均匀分布作了初步研究．反演得到各个周期面波相速度分布的主要特征是稳定的，不随资料选取而改变．30s左右Love波相速度主要受地壳厚度控制，反演得到的相速度分布与该区域已知的莫霍面深度分布有很好的对应关系．39-66s周期的Love波相速度图像随周期逐渐改变，过渡到一个主要受岩石圈下部上地幔构造活动控制的格局．在75-113s周期范围内的相速度分布图像表明，莱茵地堑等构造活动区为明显的低速区．在研究区域东北部的构造稳定地区，从20-113s周期始终显示为高速区．

Cascaded Evolution of Mantle Plumes and Metallogenesis of Core- and Mantle-derived Elements

Mineral deposits are unevenly distributed in the Earth's crust, which is closely related to the formation and evolution of the Earth. In the early history of the Earth, controlled by the gravitational contraction and thermal expansion, lighter elements, such as radioactive, halogen-family, rare and rare earth elements and alkali metals, migrated upwards; whereas heavier elements, such as iron-family and platinum-family elements, base metals and noble metals, had a tendency of sinking to the Earth's core, so that the elements iron, nickel, gold and silver are mainly concentrated in the Earth's core. However, during the formation of the stratified structure of the Earth, the existence of temperature, pressure and viscosity differences inside and outside the Earth resulted in vertical material movement manifested mainly by cascaded evolution of mantle plumes in the Earth. The stratifications and vertical movement of the Earth were interdependent and constituted the motive force of the mantle-core movement. The cascaded evolution of mantle plumes opens the passageways for the migration of deep-seated ore-forming material, and thus elements such as gold and silver concentrated in the core and on the core-mantle boundary migrate as the gaseous state together with the hot material flow of mantle plumes against the gravitational force through the passageways to the lithosphere, then migrate as the mixed gas-liquid state to the near-surface level and finally are concentrated in favorable structural expansion zones, forming mineral deposits. This is possibly the important metallogenic mechanism for gold, silver, lead, zinc, copper and other many elements. Take for example the NE-plunging crown of the Fuping mantle-branch structure, the paper analyzes ductile-brittle shear zone-type gold fields (Weijiayu) at the core of the magmatic-metamorphic complex, principal detachment-type gold fields (Shangmingyu) and hanging-wall cover fissure-vein-type lead-zinc polymetallic ore fields (Lianbaling) and further briefly analyzes the source of ore-forming material and constructs an ore-forming and -controlling model.

Tomographic investigation of the upper crustal structure and seismotectonic environments in Yunnan Province

Investigation has been made for the upper crust structure and seismotectonic environments in Yunnan Province using the plentiful DSS data of the four profiles. The derived velocity model has a good relationship with the ex-posed basins, uplifts and faults. The low velocity anomaly corresponding to the volcano also has been revealed. There exists a prominent lateral inhomogeneity within the upper crust of Yunnan region. The depth of crystalline basement generally ranges from 0 km to 5 km, and the bedrocks are exposed on the ground directly in some places, nevertheless the thickness of sedimentary cover also can reach to 8 km or even 12 km at some large depressions. Although the Changning-Shuangjiang fault is a boundary between two first class tectonic units, its incision depth within the crust maybe shallow. On the other hand, known as the plates seam, the Honghe fault has a distinct evi-dence of extending into the mid-lower crust. The widely spread activity of the volcanoes in the geological era has a close relationship with the earthquakes occurrence nowadays. Despite of the ceasing of the volcanoes in some places on the ground, the material in the mid-lower crust is still active, and there still exists strong upward stress. As the ceasing of the volcanoes on the surface, most parts of the power from the lower crust and the upper mantle cannot be released; therefore it accumulates at some appropriate tectonic locations. Moreover, the saturation of the water from the basin, the action of other fluids, and the effects of the outer stress maybe another direct reason ac-count for the strong earthquakes occurrence in Yunnan region.

Three-dimensional P velocity structure in Beijing area

A detail three-dimensional P wave velocity structure of Beijing, Tianjin and Tangshan area (BTT area) was deter-mined by inverting local earthquake data. In total 16 048 P wave first arrival times from 16048 shallow and mid-depth crustal earthquakes, which occurred in and around the BTT area from 1992 to 1999 were used. The first arrival times are recorded by Northern China United Telemetry Seismic Network and Yanqing-Huailai Digital Seismic Network. Hypocentral parameters of 1 132 earthquakes with magnitude ML=1.7~6.2 and the three-dimensional P wave velocity structure were obtained simultaneously. The inversion result reveals the com-plicated lateral heterogeneity of P wave velocity structure around BTT area. The tomographic images obtained are also found to explain other seismological observations well.

Cepstrum analysis of seismic source characteristics

This paper introduces the concept of cepstrum. By investigating the difference in source characteristics between earthquakes and explosions the paper infers the manifestation of source difference in various variable domains, and seeks for effective means to express such source difference. Extending the approach of source discrimination from time and frequency domain to the cepstrum domain, the paper proposes a method of cepstrum analysis for recognizing the characteristics of seismic sources and establishes criteria for identifying the type of seismic sources. Cepstrum analysis on some recent earthquakes and explosions has been made, and the result shows that the method is quite effective in practice.

Experimental Research on the Low Frequency Wave That Radiates into the Air before the Failure of Rock

Experiments on sonic transmission show that a slabstone can directly transmit part of the energy of a wave excited by knocking or by a transducer into the air. The other part of the wave energy can generate the normal mode of vibration on the slabstone and excite measurable acoustic signals in the air. The dominant frequency is related to the size of the slabstone. These results indicate that the acoustic emission (AE) in rock also displays similar behavior if the source is shallow. It is demonstrated that with the nucleation and propagation of cracks, the dominant frequency of the radiated wave will be lower. When the frequency becomes very low, the wave can be transmitted through the rock into the air and be received by a microphone. According to the theory of similarity of size, there will be low-frequency waves before strong earthquakes because of nucleation of cracks, which can be received by special low-frequency transducers or infrasonic detectors. Before earthquakes, the mechanism of precursors could be very complicated. They might be produced by plastic creep or attributed to liquids but not brittle fracture in most cases. So the periods of the produced waves will be longer. This perhaps accounts for the lack of foreshocks before many strong earthquakes.

Nonlinear Inversion of Potential-Field Data Using an Improved Genetic Algorithm

The genetic algorithm is useful for solving an inversion of complex nonlinear geophysical equations. The multi-point search of the genetic algorithm makes it easier to find a globally optimal solution and avoid falling into a local extremum. The search efficiency of the genetic algorithm is a key to producing successful solutions in a huge multi-parameter model space. The encoding mechanism of the genetic algorithm affects the searching processes in the evolution. Not all genetic operations perform perfectly in a search under either a binary or decimal encoding system. As such, a standard genetic algorithm (SGA) is sometimes unable to resolve an optimization problem such as a simple geophysical inversion. With the binary encoding system the operation of the crossover may produce more new individuals. The decimal encoding system, on the other hand, makes the mutation generate more new genes. This paper discusses approaches of exploiting the search potentials of genetic operations with different encoding systems and presents a hybrid-encoding mechanism for the genetic algorithm. This is referred to as the hybrid-encoding genetic algorithm (HEGA). The method is based on the routine in which the mutation operation is executed in decimal code and other operations in binary code. HEGA guarantees the birth of better genes by mutation processing with a high probability, so that it is beneficial for resolving the inversions of complicated problems. Synthetic and real-world examples demonstrate the advantages of using HEGA in the inversion of potential-field data.

The Statistical Analysis of Migration of Strong Earthquakes─Taking the North China Region as an Example

The migration of strong earthquakes is an important research topic because the migration phenomena reflect partly the seismic mechanism and involve the prediction of tendency of seismic activity. Research on migration of strong earthquakes has mostly focused on finding the phenomena. Some attempts on getting regularity were comparatively subjective. This paper suggests that there should be indices of migration in earthquake dataset and the indexes should have statistical meaning if there is regularity in the migration of strong earthquakes. In this study, three derivative attributes of migration, i.e., migration orientation, migration distance and migration time interval, were statistically analyzed. Results in the North China region show that the migration of strong earthquakes has statistical meaning. There is a dominant migration orientation (W by S to E by N), a dominant distance (≤100km and on the confines of 300～700km), and a dominant time interval (≤1a and on the confines of 3～4a). The results also show that the migration will differ slightly with different magnitude range or earthquake activity phase.

Application of the Wavelet Packet Method in Discrimination Between Nuclear Explosion and Earthquake

Although the CTBT (Comprehensive Nuclear Test Ban Treaty) was passed in 1996, it is still necessary to develop new and highly efficient methods (Wu Zhongliang, Chen Yuntai, et al., 1993; Xu Shaoxie, et al.1994; Richard L. Garwin, 1994) to monitor possible events. Many discrimination criteria (Xu Shaoxie, et al.,1994; Institute of Geophysics, Chinese Academy of Sciences, 1976; Richard L. Garwin, 1994) have been put forward since the 1950s. The results show that each of the existing criteria has its own limitation, but the seismological method is an important and efficient method in the discrimination between nuclear explosion and earthquake. Especially in recent years, because of the little and little equivalent as well as the increasing hiding steps used in the test, a number of more efficient seismological methods have been worked out. In this paper, a new discrimination method, the Wavelet Packet Component Ratio (WPCR) method, is put forward. This method makes full use of the difference in variation with time between the spectra of nuclear explosions and earthquakes. Its discrimination efficiency is rather high.

Centroid Depth Versus Hypocentral Depth: Their Distribution and Depth/Mechanism Dependence

The Harvard Global CMT catalogue from 1977 to 1998 is analyzed to investigate the relation between the centroid depth and the hypocentral depth. It is observed that for shallow earthquakes, the hypocentral depth is systematically larger than the centroid depth, while for deep_focus earthquakes there is no statistically significant difference between the distributions of centroid and hypocentral depth. A detailed look at the result reveals that such a systematic difference is mainly from the contribution of thrust and normal earthquakes, while strike_slip earthquakes have no such regularity. It turns out that for shallow thrust and normal earthquakes, seismic rupture tends to initiate from the deeper part.

Influence of uncertainty in delimitation of seismic statistical zone on results of PSHA

The seismic hazard of research area is evaluated by probabilistic analysis method for three different seismic statis-tical zone scenarios. The influence of uncertainty in seismic statistical zone delimiting on the evaluation result is discussed too. It can be seen that for those local sites along zone's border or within areas with vast change of upper bound magnitude among different scenarios the influence on seismic hazard result should not be neglected.

A study on relation between acoustic emission and characteristic displacement field on the sample with multi en echelon structures——The theoretic and experimental explorations of strain gap

Based on the phenomena that the deformation gap was observed before the great Tangshang earthquake, this paper discusses the strain gap according to test and theory. The (strain) patterns were recorded photographically by real-time holographic interferometry and shadow optical method of caustics, as soon as the loading process started. In the meantime, the AE (acoustic emission) signals were recorded by a micro crack information storage-analysis sys-tem. According to damage theory and location of micro fracture, we have studied the stain gap and gained: a) It is necessary that strain gap appears under the condition of linear elasticity theory, and its situation is relatively stable, corresponding to stress concentration. b) Micro fractures, which appear initially at area of high stress, occur rarely at the strain gap, and their locations are finally in the zone between the stress concentration area and the strain gap, which indicate the clusters or groups. However, the major macro fracture (final rupture) started from the shadow areas, and then grew quickly towards the strain gaps, which resulted in failure of sample.

Lateral variation of Pn velocity beneath northeastern marginal region of Qinghai- Xizang plateau

Pn arrival time data are collected from the bulletins of both national and regional seismological network in China. These data are tomographically inverted to map the lateral variation and anisotropy of Pn velocity in the northeast-ern marginal region of Qinghai-Xizang plateau. The average Pn velocity in this region is 8.09 km/s, being a little higher than the average for whole China. Higher velocity is found in tectonically stable Qaidam basin, while lower velocity is seen in and around tectonically active Shanxi graben. The region where the 1920 Haiyuan great earth-quake occurred shows a slightly low Pn velocity. A noticeable result is that, differing from the tectonically com-pressive Tianshan region, where Pn velocity is low, the Qilianshan region, where the Neotectonic deformation is also primarily compressive, shows high Pn velocity. In the uppermost mantle beneath the Ordos plateau Pn veloc-ity is inhomogeneous, varying from higher velocity in southwestern part to lower one in northeastern part. This may be attributed to possible movement of the Ordos block, as there are strong earthquakes all around the block.

The velocity structure of crust and upper mantle in the Wudalianchi volcano area inferred from the receiver function

The Wudalianchi volcano is a modern volcano erupted since the Holocene. Its frequent occurrence of the small earthquake is considered to be indicator of active dormancy volcano. The S wave velocity structure is inferred from the receiver function for the crust and upper mantle of the Wudalianchi volcano area. The results show that the low velocity structure of S wave is widely distributed underneath the volcano area and part of the low-velocity-zone located at shallow depth in the Wudalianchi volcano area. The low velocity structure is related to the seismicity. The Moho interface is not clear underneath the volcano area, which may be regard to be an nec-essary condition for the lava upwelling. Therefore, we infer that the Wudalianchi volcano has the deep structural condition for the volcano activity and may be alive again.

Characteristics and Implication of the Earthquake Swarm Occurred in Fuzhou in September 1999

On September 23, 1999, an earthquake swarm occurred in Fuzhou. Because the swarm occurred in the region where earthquakes occurred scarcely before and very close to the center of the city as well as shortly after the Jiji earthquake with MS7.6 in Taiwan, September 21, 1999, has aroused interest broadly. In this paper, we analyzed the characteristics of spatial and temporal distribution of the earthquake swarm and validated magnitude-number constituent of the swarm is special. In present theory, the earthquake swarm means that a small scale macro original rupture has formed in the layer of the crust in Fuzhou region where moderately strong earthquake risk exists.

Deformation Pattern and Holocene Slip Rate Along the Fukang Fault in Eastern Tianshan, China

The deformation pattern and Holocene slip rate along the Fukang fault in Eastern Tianshan, China are analyzed and studied using the data obtained in field investigation. The result indicates that the Fukang fault consists of 4 low-angle south-dipping thrust faults with stepover, displaying recent tectonic activity. The movement along the termination parts of the fault is weaker, with an average vertical slip rate of 0 13～0 33 mm/a in Holocene, and along the middle part of the fault is stronger, with an average vertical slip rate larger than 1.42 mm/a in Holocene. The Holocene deformation pattern along the fault displays generally steady slip, multi-phase intermittent movement along its western segment, and persistent movement along its middle and eastern segments, which have caused rapid dislocation up to the surface in an earlier phase.

Statistical Analysis on the Corner Period of Site-Related Design Spectra

According to the results of site seismic hazard analysis accomplished in the past decades, 96 site-related design spectra are selected as samples in this study. The result shows that the value of the corner period (T g) of the design spectrum in GBJ11-89 (China Seismic Building Code, issued in 1989) is lower than the value obtained by site seismic hazard analysis. The same situation exists when we compare the design spectra of the Codes to the spectra according to the earthquake records. The value in current seismic design code, GBJ50011-2001 issued in 2001, is greater than that in GBJ11-89, but still less than the value obtained by site seismic hazard analysis. If we accept the value got by site seismic hazard analysis, we have a suspicion that 2/3 of buildings built according to GBJ11-89 will not be safe when an earthquake with 2% probability of exceedance in 50 years occurs.

The Time-Frequency Energy Attenuation Factor and Its Application on the Basis of Gauss Linear Frequency-Modulated Continuous Wavelet Transform

Based on the Gauss linear frequency modulated wavelet transform, a new characteristic index is presented, namely time frequency energy attenuation factor which can reflect the difference features of waveform in earthquake focus mechanism, wave traveling path and its attenuation characteristics in focal area or near field. In order to test its validity, we select the natural earthquakes and explosion or collapse events whose focus mechanisms vary obviously,and some natural earthquakes located at the same site or in a very small area. The study indicates that the time frequency energy attenuation factors of the natural earthquakes are obviously different with that of explosion or collapse events, and the change of the time frequency energy attenuation factors is relatively stable for the earthquakes under the normal seismicity background. Using the above mentioned method, it is expected to offer a useful criterion for strong earthquake prediction by continuous earthquake observation.