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.

Detection of ULF electromagnetic emissions as a precursor to two earthquakes in China

The geomagnetic data recorded by Kashi and Jinghai observatories in China were analyzed with improved polarization method. We compared the result around 0.01 Hz which is thought to be useful to detect the ULF anomaly with the result around 0.1 Hz which was inferred from the earthquake depth according to the skin effect, and found that 0.1 Hz is more proper to detect the ULF anomaly for both earthquakes studied in this paper.

The Characteristics of Seismic Activity Before the Devastating Earthquake with M_W9.0 Off the West Coast of Northern Sumatra

The characteristics of seismic activity in different time-spatial domain before the M_W9.0 earthquake were studied. The results are as follows:The activity of the deep earthquakes in the north boundary zone of the Australian plate had been evidently strengthened since 1994, showing an increased frequency, magnitude and depth, especially in regards to the heterogeneous distribution of the earthquake depth (namely between 500km and 689km). Meanwhile the shallow earthquakes of M≥7.0 in the Sumatra island and its vicinity had been obviously strengthened too, and formed a strengthening area with a length of about 1000 km and width 300 km. ②The time distribution of global strong earthquakes with M≥7.0 shows that the character of anomalous seismic quiescence-activity one year before the M_W9.0 earthquake and during its active period, the strong earthquakes formed a seismic belt striking in NWW direction. At the same time, there is a seismic gap formed by earthquakes of M≥5.0 in the epicenter and its neighboring region. ③Two deep earthquakes of M≥7.0 occurred in the west and in the east of the north boundary zone of the Australian plate half year ago. It is notable that one of them occurred in the Sumatra island where no deep earthquake with M≥6.0 has occurred in the past thirty years. ④The space distribution of moderate shocks occurring three days ago exhibited a NWW-strike seismic belt along the north boundary zone of the Australian plate. ⑤The activity of volcanoes distributed in the north boundary zone of the Australian plate had been strengthened in the past 4 years, especially several months before the occurrence of the M_W9.0 earthquake.

3-D rheologic model of earthquake prepa-ration (III): Precursor field

On the basis of the theory of viscoelastic displacement and strain field for the three-dimensional rheologic model of earthquake preparation, this paper mainly studies the theoretical solution of precursor field for the three-dimensional rheologic model of earthquake preparation. We derive the viscoelastic analytical expressions of the ground tilt, underground water level, earth resistivity at an arbitrary point （x, y, z） in the rheologic medium, and analyzed the earth resistivity preliminarily, providing a certain theoretical basis for the precursor analysis of seismogenic process.

Characteristics of seismic activity before the M_S8.0 Wenchuan earthquake

The characteristics of spatio-temporal seismicity evolution before the Wenchuan earthquake are studied. The results mainly involve in the trend abnormal features and its relation to the Wenchuan earthquake. The western Chinese mainland and its adjacent area has been in the seismically active period since 2001, while the seismic activity shows the obvious quiescence of M≥7.0, M≥6.0 and M≥5.0 earthquakes in Chinese mainland. A quiescence area with M≥7.0 has been formed in the middle of the North-South seismic zone since 1988, and the Wenchuan earthquake occurred just within this area. There are a background seismicity gap of M≥5.0 earthquakes and a seismogenic gap of ML〉4.0 earthquakes in the area of Longrnenshan fault zone and its vicinity prior to the Wenchuan earthquake. The seismic activity obviously strengthened and a doughnut-shape pattern of M≥4.6 earthquakes is formed in the middle and southern part of the North-South seismic zone after the 2003 Dayao, Yunnan, earthquake. Sichnan and its vicinity in the middle of the doughnut-shape pattern show abnormal quiescence. At the same time, the seismicity of earthquake swarms is significant and shows heterogeneity in the temporal and spatial process. A swarm gap appears in the M4.6 seismically quiet area, and the Wenchuan earthquake occurred just on the margin of the gap. In addition, in the short term before the Wenchuan earthquake, the quiescence of earthquake with ML≥4.0 appears in Qinghai-Tibet block and a seismic belt of ML〉3.0 earthquakes, with NW striking and oblique with Longmenshan fault zone, is formed.

Envelope Functions of Time Histories in Seismic Safety Evaluation and Scenario Earthquakes

It has been a period of time since the concept of scenario earthquake was proposed, but this concept has rarely been used in seismic safety evaluation in China since then. Meanwhile, because of the uncertainties of magnitudes-distances pairs, there is large arbitrariness while determining the envelope function of time histories in seismic hazard analysis. In this paper, we describe a method to control the envelope functions of the time histories by introducing the most-likely combinations of magnitude and distance of the scenario earthquakes based on a probabilistic method, revise the software of the ellipse model for seismic hazard analysis, and give a computation example.

Support vector machine method for fore-casting future strong earthquakes in Chinese mainland

Statistical learning theory is for small-sample statistics. And support vector machine is a new machine learning method based on the statistical learning theory. The support vector machine not only has solved certain problems in many learning methods, such as small sample, over fitting, high dimension and local minimum, but also has a higher generalization （forecasting） ability than that of artificial neural networks. The strong earthquakes in Chinese mainland are related to a certain extent to the intensive seismicity along the main plate boundaries in the world, however, the relation is nonlinear. In the paper, we have studied this unclear relation by the support vector machine method for the purpose of forecasting strong earthquakes in Chinese mainland.

Primary component analysis method and reduction of seismicity parameters

In the paper, the primary component analysis is made using 8 seismicity parameters of earthquake frequency N (ML≥3.0), b-value, η-value, A(b)-value, Mf-value, Ac-value, C-value and D-value that reflect the characteristics of magnitude, time and space distribution of seismicity from different respects. By using the primary component analysis method, the synthesis parameter W reflecting the anomalous features of earthquake magnitude, time and space distribution can be gained. Generally, there is some relativity among the 8 parameters, but their variations are different in different periods. The earthquake prediction based on these parameters is not very well. However, the synthesis parameter W showed obvious anomalies before 13 earthquakes (MS≥5.8) occurred in North China, which indicates that the synthesis parameter W can reflect the anomalous characteristics of magnitude, time and space distribution of seismicity better. Other problems related to the conclusions drawn by the primary component analysis method are also discussed.

The characteristics of Quaternary activity of faults in the sea area near the Yangtze River mouth

By shallow seismic prospecting, it is showed that the faults in the sea area near the Yangtze River mouth are mainly the NE and NW-trending faults. The main activity time of fault is Pliocene to Early Pleistocene, and the latest activity is up to Middle Pleistocene. The maximum of fault is generally several tens meters with the throw decreased upward. The dislocation near the bottom of Middle Pleistocene is 12~13 m. The average vertical dis-placement rate is on a level of 10-3 mm/a.

Performance Metrics and Delay Thresholds for Multi-Link Cluster Monitoring in Seismic Profession

Seismic cluster nodes can be monitored by monitoring system,but thresholds for link failure alarm in monitoring systems are not determined presently,especially in different types of cluster links.Communication link types are discussed in seismic profession.By analyzing the characteristics of various links,the main performance metric,network latency,was proposed,which influenced states of communication links and gave the monitoring results deviation formula for judging the cluster monitoring system at different delay thresholds settings based on multiple-link delay error ratio analysis algorithm we offered.From the final experimental data of the monitoring system,fault alarm thresholds settings were posed under five different communication links,which had the instruction significance to the cluster monitoring in seismic profession.

Levels of Probability of Exceedance for Current Code Spectra in China

Long-period acceleration spectra determined by seismic safety evaluation for project sites are generally lower than that given by relative code spectra.In this paper,we discuss the recurrence periods corresponding to the code spectra of different periods,by using ground motion attenuation laws for sites of types Ⅰ and Ⅲ.We show the results that the longer the periods of code spectra are commonly the more conservative the seismic level is.As for the project examples in this paper,when the periods are longer than 3.7 or 5.2 seconds for sites of types Ⅰ or Ⅲ,the recurrence periods corresponding to the code spectra are longer than 5000 years.We suggest that some problems need to be further discussed,including the reliability of the present attenuation laws,the performance of those project structures that suffer long period seismic waves and have been designed according to the conservative codes,and the effects of ground motion parameters such as velocity and displacement on seismic design.

Discussion of rupture mechanisms on the seismogenic fault of the 2008 M_s8.0 Wenchuan earthquake

The May 12, 2008, Ms8.0 Wenchuan earthquake was the outcome of a recent movement of an active intra-continental thrust fault zone. The seismogenic fault of this earthquake underwent oblique-slip faulting along the central fault and pure thrust faulting along the range-front fault of the Longmenshan fault zone. The former had a steep dip and large vertical displacement, and the latter had a gentle dip and little vertical displacement. The fault zone consisted of compressive double fault ramps rup turing with right-lateral strike-slip components resulting from strain partitioning of a deep oblique slip fault in the brittle zone of the upper crust. The kinematic pattern and rupture mechanisms are complex for the seismogenic fault, as indicated by the geometric pattern of its surface ruptures, the coseismic displacement distribution and focal mechanisms of the main shock and aftershocks. As a tear fault, the NW-trending, left-lateral, strike-slip Xiaoyudong fault zone has accommodated NE-trending displacements with different shortening amounts. However, because of intense compression on the southwestern segment of the seismogenic fault, the left-lateral, strike-slip Xiaoyudong fault also carries a clear compression component. Normal faulting with a strike-slip component controls the formation of a fault-trough along the central fault, which is characterized by thrusting with a strike-slip component and strike-slip with thrusting. The fault-troughs are the product of the interaction of slip and grav ity on the seismogenic fault under specific geological and geomorphic conditions. Gravitational force exaggerated the vertical component of fault displacement, which by no means represents the actual maximum vertical displacement of the seismogenic fault.

Statistical study on great geomagnetic storms during solar cycle 23

Characteristics of great geomagnetic storms during solar cycle 23 were statistically investigated. Firstly, we focused on the uniqueness of solar cycle 23 by analyzing both the great storm number and sunspot number from 1957 to 2008. It was found that the relationship between the sunspot number and great storm number weakened as the activity of the storms strengthened. There was no obvious relationship between the annual sunspot number and great storm number with Dst≤-300 nT. Secondly, we studied the relationship between the peak Dst and peak Bz in detail. It was found that the condition Bz〈-10 nT is not necessary for storms with Dst≤-100 nT, but seems necessary for storms with Dst≤-150 nT. The duration for Bz≤-10 nT has no direct relationship with the giant storm. The correlation coefficient between the Dst peak and Bz peak for the 89 storms studied is 0.81. After removing the effect of solar wind dynamic pressure on the Dst peak, we obtained a better correlation coefficient of 0.86. We also found the difference between the Dst peak and the corrected Dst peak was proportional to the Dst peak.

青藏高原东缘汶川地震断层陡坎类型与级联破裂模型(英文)

The post-earthquake field investigations reveal that the MW7.9 Wenchuan earthquake of 12th May 2008 ruptured three NE-striking imbricate reverse faults and another NW-trending reverse fault, along the middle Longmenshan fold-and-thrust belt at the eastern margin of the Tibetan plateau. The fault-scarp features can be categorized into eight groups: simple thrust scarp, hanging-wall collapse scarp, simple pressure ridge, dextral pressure ridge, fault-related fold scarp, back-thrust pressure ridge, local normal fault scarp and crocodile-mouth-like scarp. The local normal scarp is first discovered in the reverse-faulting earthquakes as ever reported in the world. Field observation indicates that the Wenchuan earthquake surface rupture is dominated by reverse faulting with a minus right-lateral component, but the relative ratio varies from site to site. Also, the surface ruptures can be divided, for the first order, into two segments, the Yingxiu and Beichuan segments, corresponding to MW7.8 and MW7.57 events, respectively. The two segments further can be divided, for the second order, into four sub-segments in total, which are equivalent to four sub-events of MW7.46, MW7.69, MW6.99 and MW7.52, respectively. The fault segmentation, for different orders, shows a cascade-rupturing pattern and can explain why the quake time of the Wenchuan earthquake was so long as up to 100 second. Aftershock focal mechanisms are also used to constrain the fault geometry for the sub-segments, indicating that the seismogenic faults are listric at depth and in general, the fault plane becomes steeper northward, which enables the fault to accommodate larger strike-slip motion. This earthquake also confirms that the crustal shortening across the Longmenshan fold-and-thrust belt should be responsible for the growth of high topographic relief along the eastern margin of the Tibetan Plateau.

Branched tetraether lipids in Chinese soils:Evaluating the fidelity of MBT/CBT proxies as paleoenvironmental proxies

The ubiquitous occurrence of branched glycerol dialkyl glycerol tetraethers(br GDGTs) in soils has allowed development of new proxies for reconstruction of past climate and environment. The methylation and cyclization degrees of br GDGTs, expressed as MBT and CBT, respectively, are reported to be mainly controlled by mean annual air temperature(MAAT) and soil p H. However, the br GDGT-derived temperatures and soil p H scatter widely when data from different environmental conditions are considered. In this study, we collected over 300 soil samples from China, which are representative of humid(Xishuangbanna, Guangzhou, and Shanghai), semi-arid(Dongying) and semi-arid/arid(Lanzhou, Tibetan Plateau) regions. Collectively we have the most extensive dataset that broadly characterizes the distribution of br GDGTs according to climate zones in China. The overall data demonstrate that the MBT/CBT derived temperatures better match the measured MAATs in humid and non-alkaline regions than those from regions of low MAP(<400 mm/yr) and above neutral soil p H(>7.0–7.5). Similarly, CBT describes soil p H much better in humid and non-alkaline soils than in semi-arid/arid and alkaline soils; the semi-arid/arid and alkaline soils tend to show a positive correlation between soil p H and CBT, which contradicts that in the humid and non-alkaline soils. While soil p H, MAAT and mean annual precipitation(MAP) are dominating factors controlling the br GDGT distribution across all climate zones, conductivity, total organic carbon and total nitrogen, as well as soil water content can also play an important role locally. Removing br GDGT-II resulted in a revised CBT index that provides more accurate estimation of p H, especially in semi-arid/arid and alkaline soils. The overall Chinese dataset demonstrates that continental air temperature derived from br GDGT-proxies can vastly deviate from real measurements and should be used with extreme caution in paleo-climate or-environment studies.