Analysis of Geological Background of Seismic Activity in the Chengdu Plain from Data of Seismic Prospecting for Oil

Summarizing the existing data of seismological and geological investigations and of strong and intermediate-strong earthquakes in‘ the Sichuan basin and its adjacent areas accumulated by the seismological and petroleum organizations in Sichuan and of the results of seismic prospecting and detailed exploration in Chengdu depression during the last 20 years permitted us to studythe types and distribution of hidden structures in Chengdu depression and its adjacent areas, in particular, to identify in, detail the “hidden faults” in the Chenngdu-Deyang area on the one hand; The obtained data indicate that the NE-trending Xinjin fault ruus northward and dies out in the south of Penzhen town of Shuangliu County; Meanwhile, we studied genetic relations of seismic activity to active faults and their corresponding movernent charaeteristics on the other hand, Moreover, the Surface faults and deep-seated faults are clearly defined and outlined,and 5 types of seismogenic faults suggestd. The knowledge thus obtained enables us to delimit the focal zones for potential strong earthquakes in Chengdu depression. The study suggests that a zone of 40 km wide and more than 100 km long on sides along the Chengu Deyang lim bas a stable seismogeological background and good engineering-seismological conditions.     

Passive Seismic Experiment “13 BB Star” in the Margin of the East European Craton,Northern Poland

The lithosphere-asthenosphere boundary (LAB) is investigated recently very effectively, mostly using seismic methods because of their deep penetration and relatively good resolution. The nature of LAB is still debated, particularly under “cold” Precambrian shields and platforms. Passive experiment “13 BB star” is dedicated to study deep structure of the Earth’s interior in the marginal zone of the East European craton in northern Poland. The seismic network consists of 13 broadband stations on the area of ca. 120 km in diameter. The network is located in the area of well-known sedimentary cover and crustal structure. Good records obtained till now, and expected during next 1-year long recording campaign, should yield images of detailed structure of the LAB, ?410”, “?520”, and ?660” km discontinuities, as well as mantle-core boundary and inner core.     

Seismic Data Acquisition Techniques on Loess Hills in the Ordos Basin

High-resolution exploration for lithologic targets confronted with difficulties due to the original brought out from geophysical and geologic characteristics of the loess hills and the very thick deserts in Ordos. Scientific research since mid 1990s has conducted three acquisition techniques including the high-resolution crooked line survey in valleys, high-resolution multiple straight line survey and 3D survey, under different surface conditions and for different geological targets.     

Seismic Monitoring of Poland–Description and Results of Temporary Seismic Project with Mobile Seismic Network

The paper describes a temporary seismic project aimed at developing the national database of natural seismic activity for seismic hazard assessment, officially called “Monitoring of Seismic Hazard of Territory of Poland” (MSHTP). Due to low seismicity of Poland, the project was focused on events of magnitude range 1–3 in selected regions in order to maximize the chance of recording any natural event. The project used mobile seismic stations and was divided into two stages.Five-year measurements brought over one hundred natural seismic events of magnitudes M_L range 0.5–3.8. Most of them were located in the Podhale region in the Carpathians. Together with previously recorded events this made it possible to conduct a preliminary study on ground motion prediction equation for this region. Only one natural event, of magnitude M_L = 3.8, was recorded outside the Carpathians in a surprising location in central-west Poland.     

Discussion on the Relation Between the Probabilistic Distribution of Magnitude in a Seismic Province and That in an Area with Potential Seismic Source

According to the joint probabilistic distribution model of magnitude and space,the author discusses the relationship between the probabilistic distribution of magnitude in a seismic province and that in an area with potential seismic sources.The results show that if the magnitude probabilistic distribution follows the truncated exponential form in a seismic province,there must be some potential source in which the magnitude probabilistic distribution does not conform to that form.The result is consistent with the concept of "characteristic earthquake" derived from the study of actual records of seismicity and the study of geology.The author suggests that the relationship between the probabilistic distribution of magnitude in a seismic province and that in a seismic potential area must be considered in the study of the analysis of seismicity,seismic zonation and engineering seismology,for the purpose of the evaluation of the probabilistic distribution of magnitude correctly in every area with potential s     

Seismic Data Processing and Interpretation on the Loess Plateau, Part 2： Seismic Data Interpretation

The loess plateau covering the North Shaanxi slope and Tianhuan depression consists of a regional monocline, high in the east and low in the west, with dips of less than 1^0, Structural movement in this region was weak so that faults and local structures were not well developed. As a result, numerous wide and gentle noses and small traps with magnitudes less than 50 m were developed on the large westward-dipping monocline. Reservoirs, including Mesozoic oil reservoirs and Paleozoic gas reservoirs in the Ordos Basin, are dominantly lithologic with a small number of structural reservoirs. Single reservoirs are characterized as thin with large lateral variations, strong anisotropy, low porosity, low permeability, and low richness. A series of approaches for predicting reservoir thickness, physical properties, and hydrocarbon potential of subtle lithologic reservoirs was established based on the interpretation of erosion surfaces.     

Changes in the Frequency-Energy Distribution of Seismic Events During Mining in the Ostrava-Karviná Coal Field

The relation between the number of seismic events N and their magnitude and/or energetic magnitude is one of the basic relations in the statistics of earthquakes and mining-induced events. A detailed analysis of the b-values in the relation log N =a–b logE for the induced seismic events occurring in the Ostrava-Karviná Coal Basin is given in this paper. The least-squares method, as well as the maximum likelihood method were applied in solving this problem mathematically. Based on the results of frequency-energy distribution analysis, it was proved that the variations of b-values in space and time do exist, and that these values are inversely proportional to the level of induced seismicity influenced by the various mining activities being carried out in-situ. This statement could, in general, be supported by the fact that lower b-values correspond to higher seismic activity, while higher b-values correspond to low and moderate seismic activity.     

Reconstruction of the Solar Activity in 1000–1700 Based on Auroral Data with Allowance for the Contribution of the Main Magnetic Field of the Earth

Geomagnetism and Aeronomy - A new reconstruction of the number of sunspots (SN) in 1000–1700, along with possible errors, has been obtained based on an analysis of auroral observations at...     

A Preliminary Investigation of the Application of Modern Crustal Deformation Data in Seismic Zonation

INTRODUCTIONAs a high precision and lowcost tool,the global positioning system(GPS)allows easy andversatile observation anditis suitablefor dense deployment.Because of these merits,it has been usedto monitor crustal deformation andtostudytectonic movement on various scales,fromlocal segment offaults to global plates(Gan Weijun,2001).In recent years,GPS observation data has beenunceasingly enriched.Thus,it would be a very worthwhile effort to analyze the features of earthquakeoccurrence…     

Characteristic Features of Solar Cosmic Rays in the 21st–24th Solar-Activity Cycles According to Data from Catalogs of Solar Proton Events

Geomagnetism and Aeronomy - Homogeneous series of solar cosmic-ray events for four solar-activity cycles against the background of decreased activity in cycles 23 and 24 are considered. The number...     

Research on the Result of Calibration for the Location of the Seismic Array in Shanghai

The paper proposes the calibration theory and methods for the Shanghai seismic array and analyzes the calibration results. As a result, the calibration results for the seismic array based on 2 typical earthquakes have been drawn; the difference of calibration results between Hokkaido and Honshu region in Japan is investigated. And calibration results of different directions, different epicenter distances and different magnitudes are probed into. The result shows that the location of earthquakes on the Shanghai seismic array is greatly improved.     

The Results and Comparison of "Logical-Tree" Seismic Zoning in the Panxi Area

On the basis of the technological route of seismic hazard analysis,the methods for determining seismicity parameters,such as b value,annual occurrence rate,and the seismic spatial distribution function,are discussed.Then,the seismic intensity zoning in Panxi area in Southwest China is carried out by applying the "logical-tree,"which is made up of multi-parameter schemes.It is clearly shown from the results that seismic intensity zoning is influenced by many uncertain factors and it is necessary to seek a certain balance between seismic safety and investment interest and a good way,with the present limited knowledge level,to obtain seismic intensity zoning is through the "logical-tree" method.     

Research on the Seismic Vulnerability of Building Structure in Sichuan Province

Research on the seismic vulnerability of building structures is very important for the work of earthquake disaster preparedness and mitigation.On the basis of the related studies over a long time,this paper provides several seismic vulnerability matrices of building structure in different regions of Sichuan Province,Poor anti-seismic capability is one of the factors resulting in the earthquake disasters in the past.We can reduce economic losses caused by earthquake through improving the anti-seismic and prevention level of building structures in Sichuan Province.     

Analysis of Seismic Activity in the Middle Part of the North-South Seismic Belt—Joint Study on Deep Seismic Sounding Profile and Seismicity Parameters

Using the rich deep seismic sounding data recorded in the middle part of the North-South Seismic Belt in China, the horizontal and vertical profiles are constructed to obtain the seismic velocity structure, analyze the seismic distribution and calculate the seismic energy and the thickness of the seismogenic layer at the same time. On this basis, the seismicity parameters are calculated using the earthquake catalogue of the study area for the past 40 years, and the relationship between the b-value distribution and the velocity structure is analyzed. The results show an uneven b-value distribution in the study area and a segmented feature along the Longmenshan fault zone. Most of the earthquakes occur in the transition zone anomalies from the positive to the negative. In addition, the thickness of the crust drops from ~60 km to ~48 km from the Southeastern to the Northeastern Qinghai-Tibetan Plateau, but the thickness of the seismogenic layer increases gradually. It is speculated that the crustal composition of the Northeastern margin contains more felsic materials and has relatively stronger seismic activities than the Southeastern Qinghai-Tibetan Plateau, possibly associated with the subduction and compression of the Indian Ocean Plate.     

2D Seismic Data Processing for Straight Lines in the Loess Plateaus in Fuxian of Shanbei

The crooked seismic lines along valleys were irregular previously in Fuxian of Shanbei,showing an irregular branch in plane, and hard to complete close grids. Therefore, it‘s difficult to conduct reservoir inversion of 2D seismic data. In 2001, Zhongyuan Oilfield Company carried out the study on field acquisition methods and seismic processing technology in Fuxian. Straight lines were passing through plateaus and formed seismic grids by using flexible geometry with variable linear bins.Data processing involved model-inversion based refraction static correction, surface consistent amplitude compensation, deconvolution, and pre-stack noise attenuation. As the result, seismic data with a high fidelity was provided for the subsequent reservoir predictions, small-amplitude structure interpretation and integrative geologic study. Because all lines were jointed to form grids, comprehensive interpretation of reservoir inversion could be finally implemented by using the pseudo logging method to control lines without wells.     

Estimation of Seismic Velocities from Deep Reflections in the τ-p Domain

—In deep reflection seismics the estimation of seismic velocities is hampered in most cases due to the low signal level with respect to noise. In the τ-p domain, it is possible to perform the velocity analysis even under such unfavorable signal conditions. This is achieved by making use of special properties of the transform, which enhance the signal-to-noise ratio. Further noise suppression is realized by incorporating filter procedures into the transform algorithm. The velocity analysis itself is also done in the τ-p domain by calculating and evaluating constant velocity gathers. The results can be directly used in the time domain. A mute algorithm, implemented into the τ-p velocity analysis procedure, further reduces noise. This velocity estimation method is discussed with synthetic data and applied to DEKORP data.     

Preliminary Study on the Effect of Borehole on Seismic Waves in the Deep Borehole Observation System

There has been an increasing tendency to adopt the deep borehole technique for seismic observation.This paper deals with the effect of borehole on seismic waves in the deep borehole system and obtains the conclusion that,within the frequency range of seismic waves,the existence of a borehole has no effect on the horizontal component of a three-component seismometer in the borehole and has only a limited effect on the vertical component.To the first approximation,the difference between the borehole record and ground surface record of seismic waves can be attributed to the difference in seismometer deployment. This conclusion would be useful for the integrated utilization of borehole records and ground surface records of seismic waves.     

Reconstruction of Heliospheric Modulation Potential Based on Radiocarbon Data in the Time Interval 17 000–5000 Years B.C.

Geomagnetism and Aeronomy - The results of reconstruction of the heliospheric modulation potential based on radiocarbon data for the time interval 17 000–5000 years B.C. are presented....     

Seismic tomography and anisotropy in the source area of the 2008 Iwate–Miyagi earthquake (M 7.2)

In order to understand the generation mechanism of the Iwate–Miyagi earthquake (M 7.2) that occurred on 14 June 2008 in Northeast Japan, we determined high-resolution 3D seismic velocity (Vp, Vs) and Poisson's ratio (σ) structures as well as P-wave azimuthal anisotropy in and around the source area using 246,623 P-wave and 189,153 S-wave high-quality arrival times from 1941 aftershocks of the 2008 Iwate–Miyagi earthquake as well as 4878 shallow and intermediate-depth earthquakes in this area recorded by the dense High-Sensitivity Seismic Network (Hi-net) and the seismic stations of Tohoku University. Our results show that hypocenters of the mainshock and three large aftershocks are located in a boundary zone where both seismic velocity and Poisson's ratio change drastically in a short distance. A zone with pronounced low-velocity and high Poisson's ratio is revealed in the lower crust and uppermost mantle under the source area, which may reflect the arc magma and fluids ascending from the upper-mantle wedge. The P-wave azimuthal anisotropy is complex under the study area, which may also indicate the complex crustal structure there. These results indicate that the generation of the 2008 Iwate–Miyagi earthquake was influenced by the ascending arc magma and fluids associated with the dehydration reactions of the subducting Pacific slab under Northeast Japan.