Decline of groundwater table in Beijing and recognition of seismic precursory information

This paper quantitatively analyzed groundwater table fluctuations caused by groundwater overdraft, and probed into the possibility of drawing earthquake precursory information from groundwater table variations on the background of groundwater overdraft. Main effect factors of groundwater regime in Beijing region include groundwater extraction and rainfall. The decline of groundwater table was directly related to regional groundwater overdraft. Using the method of correlation analysis, the paper analyzed the relation between groundwater overdraft and groundwater level variations, with the aim of evaluating the effect of groundwater overdraft on water levels in observation wells and providing scientific basis for identifying seismic precursory information. The results indicate that the variations of groundwater level in slightly-affected zones of groundwater overdraft can contain some seismic precursory information, and it is possible to extract seismic precursory anomalies if proper mathematical methods are adopted to remove the trend component and annual period changes.

Seismic Sequence Characteristics and Precursory Anomalies of the M_S6.3 and M_S6.4 Da Qaidam Earthquakes in 2008～2009

In this paper,the seismogenic structures of the Da Qaidam strong earthquakes are preliminarily discussed by using the regional seismotectonic data and focal mechanism solutions. Analysis is done on the temporal and spatial distribution characteristics of the two strong earthquake sequences in Da Qaidam in combination with the sequence distribution characteristics of the M6. 6 earthquake of 2003 and the five strong earthquakes of about M5. 0 in 2004 in Delingha. At the same time,the regional characteristics of the historical seismic activity are also investigated. Preliminary analysis is done on the influence of the two M8. 0 earthquakes in the past 10 years on this region. Precursory anomalies and their characteristics are discussed in combination with the analysis of the precursor observation data of Qinghai Province.

Distinctive Precursory Air–Sea Signals between Regular and Super El Ni os

Statistically different precursory air–sea signals between a super and a regular El Ni no group are investigated, using observed SST and rainfall data, and oceanic and atmospheric reanalysis data. The El Ni no events during 1958–2008 are first separated into two groups： a super El Ni no group（S-group） and a regular El Ni no group（R-group）. Composite analysis shows that a significantly larger SST anomaly（SSTA） tendency appears in S-group than in R-group during the onset phase[April–May（0）], when the positive SSTA is very small. A mixed-layer heat budget analysis indicates that the tendency difference arises primarily from the difference in zonal advective feedback and the associated zonal current anomaly（u）.This is attributed to the difference in the thermocline depth anomaly（D） over the off-equatorial western Pacific prior to the onset phase, as revealed by three ocean assimilation products. Such a difference in D is caused by the difference in the wind stress curl anomaly in situ, which is mainly regulated by the anomalous SST and precipitation over the Maritime Continent and equatorial Pacific.

Anomalies of Precursory Group and Grouped Strong Earthquakes in the Sichuan-Yunnan Region

Three methods of extracting the information of anomalies of a precursory group are put forward, i.e., the mathematical analyses of the synthetic information of earthquake precursors (S), the inhomogeneous degree of precursory groups (ID) and the values of short-term and impending anomaly in near-source area (NS). Using these methods, we calculate the observational data of deformation, underground fluid and hydrochemical constituents obtained from different seismic stations in the Sichuan-Yunnan region and conclude that the synthetic precursory anomalies of a single strong earthquake with M S6.0 differ greatly from those of the grouped strong earthquakes, for the anomalous information of precursory groups are more abundant. The three methods of extracting the synthetic precursory anomaly and the related numerical results can be applied into the practice of prediction to the grouped strong earthquakes in the Sichuan-Yunnan region. Inhomogeneous degree (ID) of synthetic precursory anomaly can be identified automatically because it takes the threshold of distributive characteristics of the anomalies of precursory group as its criterion for anomaly.

Abnormal interruption of water flow from an artesian well prior to 2008 Wenchuan earthquake

Water flow from an artesian well stopped on December 17, 2007 but recovered when the Wenchuan Ms 8.0 earthquake occurred on May 12, 2008. This well is located 90 km south of the epicenter in an extensional tectonic setting, where similar changes of water level and resistivity were observed at two other nearby sites. Our investigation suggests that this phenomenon was not caused by environmental disturbances, such as drought or borehole-drilling activity, but might be a precursor to the earthquake.

Characteristic Analysis of Anomalies of Strong Earthquakes along the Tancheng-Lujiang Fault Zone and Both Its Sides

This article made a systematic statistical analysis on the duration,spatial distribution,form,range,type and reliability of precursory anomalies based on the observations of precursors of 24 moderate-strong earthquakes occurring along the Tancheng-Lujiang fault zone and its bilateral areas in Shandong,Liaoning,Hebei,Jiangsu and Jiangxi Provinces in the period from 1966 to 2005. Results show that:( 1) For M7. 0 and M6. 0earthquakes,med-term abnormities are the greatest in number,short-term abnormities come second,and imminent anomalies are the least. For M5. 0 earthquakes,short-term abnormities are often the most in number,imminent anomalies come second,and the med-term ones are the least.( 2) Precursory anomalies are periodical,part of the med and short-term anomalies are shown as short-term and imminent anomalies during their development.( 3) The development of precursor shows quasi-synchronism; the closer to earthquake occurrence time,the more turning changes of anomalies will appear.( 4)Anomalies mainly occur within an epicenter distance of 100 km, showing a relative concentrated distribution in space,and the shorter the distance to epicenter,the higher the anomaly station / item rate.( 5) The spatial distribution of anomalies is relatively correlated to the strike of structures,having a good consistency with the structure.( 6)There is no significant correlation between duration of abnormities and the epicenter distance.( 7) The higher the magnitude of the earthquake,the greater the amplitude of the abnormities measured with the same observation approach.( 8) In terms of the itemsof the observations,fluid abnormities are the greatest in number,followed by deformation and electromagnetism observations.( 9) For all observation items,med and short-term abnormities make up the majority and short-term and imminent anomalies the minority.( 10) In fluid,deformation and electromagnetism observations,fairly reliable anomalies are about double the number of reliable anomalies.

A Study on the Characteristics of Anomalies and Their Dynamic Relationship before the April 14, 2010 M_S 7.1 Yushu Earthquake

The authors studied the seismic activity, precursory anomalies and abnormal animal behavior before the April 14, 2010 Ms 7.1 Yushu earthquake. Analysis showed that anomalies were not rich before the Ms 7.1 Yushu earthquake, but prominent anomalies were observed, such as the long and mid-term trend anomaly characterized by the seismic quiescence of Ms6. 0, MsS. 0 and Ms4.0 earthquakes, and the anomalies in precursor observation of surface water temperature in Yushu and Delingha and electromagnetic measurement in Ping＇an. There were a large number of animal behavior anomalies appearing one week before the earthquake. An M4.7 earthquake occurred 130 minutes before the main shock. In this paper, we studied the dynamic process of the Yushu earthquake preparation using the earthquake focal mechanism solutions on the Bayan Har block boundary since 1996. The results show that the Kalakunlun M7.1 earthquake in 1996, the Mani M7.5 earthquake and the Yushu Ms7.1 earthquake have the same dynamic process. Long and mid-term trend anomalies may be related to the dynamics of evolution of different earthquakes. This paper also discusses the recurrence interval of strong earthquakes, foreshock identification and precursor observation of the Yushu Ms7. 1 earthquake.

Regional Tectonic Deformation Background and Medium- and Short-Term Precursors to the Minle-Shandan Earthquakes1

Using GPS observations of horizontal movement from 2001 to 2003 and the cross-fault mobile short-levelling data of 1988～2003, and with the aid of the improved negative dislocation model and the time-varying curve of strain intensity ratio of fault deformation, the regional tectonic deformation background and medium- and short-term precursors related to the preparation of the Minle-Shandan earthquakes of M S6.1 and M S5.8 on October 25, 2003 are investigated. The results reveal that, under the background of the wide-range deformation adjustment, short-term relaxation and recovery caused by the Kunlun Mountains earthquake of M S8.1, the hypocenters of the earthquakes are located on the north edge of the shear stress enhancement zone between the compressional locked segments of block boundary fault, a place which may represent an accelerated strain accumulation. An obvious anomaly of strain intensity ratio appeared in short-levelling measurements crossing over the fault at the Shihuiyaokou site, the closest to the epicenters, 3 months before the occurrence of the earthquakes. In addition, the variation in number of anomalies from 10-odd days to months before the earthquakes in the entire monitoring area and the anomaly concentration and local enhancement relative to near source in the 3 months before the earthquakes are regarded to be precursors to the two events.

Study on the Method of Short-Term Synthetic Earthquake Prediction in the North China Region

Based on the extraction and calculation of the short-term seismic precursory information magnitude from the 114 major precursory observations in the North China region, and together with consideration of factors such as geological structure, seismicity, crustal thickness, and in particular, the current geodynamics of the region, the authors studied the time-space evolution characteristics of the short-term earthquake precursory information magnitude and its relationship with earthquakes and proposed the index and method for the short-term synthetic prediction of earthquakes with M S≥5.0 in the North China region. The inspection through R-value shows that the method is effective to a certain extent for earthquake prediction.