Late-Quaternary Slip Rate and Seismic Activity of the Xianshuihe Fault Zone in Southwest China

The Xianshuihe fault zone is a seismo-genetic fault zone of left-lateral slip in Southwest China. Since 1725, a total of 59 Ms ≥ 5.0 earthquakes have occurred along this fault zone, including 18 Ms 6.0–6.9 and eight Ms ≥ 7.0 earthquakes. The seismic risk of the Xianshuihe fault zone is a large and realistic threat to the western Sichuan economic corridor. Based on previous studies, we carried out field geological survey and remote sensing interpretation in the fault zone. In addition, geophysical surveys, trenching and age-dating were conducted in the key parts to better understand the geometry, spatial distribution and activity of the fault zone. We infer to divide the fault zone into two parts： the northwest part and the southeast part, with total eight segments. Their Late Quaternary slip rates vary in a range of 11.5 mm/a –（3±1） mm/a. The seismic activities of the Xianshuihe fault zone are frequent and strong, periodical, and reoccurred. Combining the spatial and temporal distribution of the historical earthquakes, the seismic hazard of the Xianshuihe fault zone has been predicted by using the relationship between magnitude and frequency of earthquakes caused by different fault segments. The prediction results show that the segment between Daofu and Qianning has a possibility of Ms ≥ 7.0 earthquakes, while the segment between Shimian and Luding is likely to have earthquakes of about Ms 7.0. It is suggested to establish a GPS or In SAR-based real-time monitoring network of surface displacement to cover the Xianshuihe fault zone, and an early warning system of earthquakes and post seismic geohazards to cover the major residential areas.

Stress interactions between normal faults and adjacent strike-slip faults of 1997 Jiashi earthquake swarm

During a 4-month period starting from 21 January, 1997, an earthquake swarm of seven major events (Ms≥6.0) struck the Jiashi region at the northwestern corner of the Tarim Basin in Xinjiang,, China. Previous relocation studies suggested that these strong earthquakes had occurred along at least two parallel rupture zones. According to the relocated hypocenters and focal mechanisms of the events, we have constructed fault models for these seven earthquakes to calculate the Coulomb stress changes produced by each of these events. Furthermore, we extended our model calculations to include an ad- jacent 1996 Ms=6.9 Artushi earthquake, which occurred one year before the Jiashi earthquake swarm. Our calculations show that the Coulomb stress change caused by the preceding events was around 0.05 MPa at the hypocenter of the 4th event, and higher than 0.08 MPa at the hypocenters of the 2nd, 3rd, 5th and 6th events. Our results reveal a Coulomb stress interactive cycle of earthquake triggering between two adjacent normal and strike-slip faults.

Analysis of the Motion and Deformation Characteristics along the Zhangjiakou-Bohai Fault

We have collected GPS data in the period of 1999-2007 from the Crustal Motion Observation Network of China along the Zhangjiakou-Bohai fault and its adjacent regions to study the characteristics of present-day crustal horizontal motion velocities in the research zone.Strain rate components are computed in the spheric coordinate system by the least square collocation method.According to the spatial distribution of the principal strain rate,dilation rate and maximum shear strain rate derived from GPS measurements,this paper analyses the deformation of the subordinary faults of the Zhangjiakou-Bohai fault.The principal compression strain rates are apparently greater than the principal extension strain rates.The larger shear strain rate is mainly in and around the Xianghe,Wenan and Tangshan areas in Hebei Province.According to the profiles across different segments of the Zhangjiakou-Bohai fault,the three segments glong the Zhangjiakou-Bohai fault show an obviously left-lateal strike-slip and compression characteristics.By analysis of the motion characteristics of the blocks,e.g.the Yanshan block,North China Plain block,Ordos block,and Ludong-Huanghai block in and around the North China region,this paper speculates that the dynamics of the motion styles of Zhangjiakou-Bohai fault may directly come from the relative movement between the Yanshan block and the North China plain block,and the ultimate dynamics may be the results of the collison between Indian plate and Eurasian plate,and the persistent northeastward extrusion of the Indian plate.

Fault-Plane Solution of the Earthquake of 19 March 2005 in Monatele (Cameroon)

An earthquake of magnitude Ml = 3.04 was detected on the 19 of March 2005 at 11:49:18.31 (local time) by seven broadband seismometers located around Cameroon (Central Africa). Its epicenter has been relocated and found to be in Monatele (Cameroon) with latitude 4°26.34' and longitude 10°59.62'. The fault-plane solution calculated using double couple fault-plane solutions based on P-wave polarity readings, also taking into consideration the dextral nature of the Sanaga Fault (SF) underlying this region of the epicenter, is a strike-slip fault with a normal faulting component. The beach ball representation of this fault-plane solution has strike, dip and rake values of 289, 70, -169 for the principal fault plane and 195, 80, -20 for the auxiliary fault plane.

Nanpu Sag of the Bohai Bay Basin:A Transtensional Fault-Termination Basin

The Nanpu（南堡） sag has previously been modeled as（1） a pull-apart basin,（2） a rift ba-sin,without significant strike-slip deformation,and（3） a transtensional basin.We present a new model for the Nanpu sag in which the basin is a transtensional fault-termination basin.Although transten-sional fault-termination basins is an important basin type,it is not as well studied as other classic basin types.On the base of 3D seismic data interpretation,the faults geometries and kinematics and their controls on depocenters are presented.The Nanpu sag is developed in the context of dextral transten-sion of the Bohai（渤海） Bay basin and attributed to a transtensional fault-termination basin.During deposition of the Es3-Es2 members,the basin border Xi＇nanzhuang（西南庄） fault and Baigezhuang（柏各庄） fault linked to a mixed normal and strike-slip fault system,or a linked fault system controlled the basin by dominant extension and weak strike-slip and created fan-shaped depocenters surrounded by the two faults.From Es1 Member to Dongying（东营） Formation,two major depocenters controlled by two mixed normal and sinistral strike-slip fault systems are located on the Linque（林雀） and Caofeidian（曹妃甸） subsags.During deposition of the Guantao（馆陶）-Minghuazhen（明化镇） Forma-tion,the Nanpu sag successively developed and significantly expanded.