Summary. Using modelled and simulated data for comparison of several methods to compute GPS strain rate fields in terms of their precision and robustness revea

This paper presents the coseismic displacement and preseismic deformation fields of the Lushan M _S7.0 earthquake that occurred on April 20, 2013. The results are based on GPS observations along the Longmenshan fault and within its vicinity. The coseismic displacement and preseismic GPS results indicate that in the strain release of this earthquake, the thrust rupture is dominant and the laevorotation movement is secondary. Furthermore, we infer that any possible the rupture does not reach the earth’s surface, and the seismogenic fault is most likely one fault to the east of the Guanxian-Anxian fault. Some detailed results are obtainable. (1) The southern segment of the Longmenshan fault is locked preceding the Lushan earthquake. After the Wenchuan earthquake, the strain accumulation rate in the southeast direction accelerates in the epicenter of the Lushan earthquake, and the angle between the principal compressional strain and the seismogenic fault indicates that a sinistral deformation background in the direction of the seismogenic fault precedes the Lushan earthquake. Therefore, it is evident that the Wenchuan M _S8.0 earthquake accelerated the pregnancy of the Lushan earthquake. (2) The coseismic displacements reflected by GPS data are mainly located in a region that is 230 km (NW direction) × 100 km (SW direction), and coseismic displacements larger than 10 mm lie predominantly in a 100-km region (NW direction). (3) On a large scale, the coseismic displacement shows thrust characteristics, but the associated values are remarkably small in the near field (within 70 km) of the earthquake fault. Meanwhile, the thrust movement in this 70-km region does not correspond with the attenuation characteristics of the strain release, indicating that the rupture of this earthquake does not reach the earth’s surface. (4) The laevorotation movements are remarkable in the 50-km region, which is located in the hanging wall that is close to the earthquake fault, and the corresponding values in this case correlate with the attenuation characteristics of the strain release.

In this paper, a unified model and method to establish the velocity field of horizontal movement and the strain field using GPS data based on the principle of least squares collocation are proposed. Meanwhile, some questions are discussed, which include the influence of different reference data in describing the velocity field and its geometric deformation meanings, and the influence of different scales of space and frequency domain on the described strain field. Then, the GPS data collected from the regional networks of Crustal Movement Observation Network of China is processed and analyzed. Lastly, the model and method proposed in this paper are applied to the whole mainland and capital region of China, which have different spatial scales.

The fault cutting algorithm is important when applying the three-dimensional numerical manifold method to engineering simulation. This paper presents a primary approach to the fault cutting algorithm, including data structures, fault cutting procedures, and some basic computing algorithms. First, the data structures of the physical elements and mathematical covers are proposed as single linked lists and linked list arrays, respectively. This reduces the complexity of the algorithm and increases the efficiency when connecting physical elements to covers. Second, a strategy of recording cutting traces between every two faults to ensure that the model agrees with the actual situation was proposed. This strategy also reduces the complexity and improves the efficiency. Third, the mathematical covers and physical elements are cut with all faults independently to process complete cutting instances in a multiblock form and incomplete cutting instances without forming any new irrational block. Finally, fou...

The spatiotemporal deformation response of a seismogenic fault to a large earthquake is of great significance to understanding the nucleation and occurrence of the next strong earthquake. The Longmeshan fault, where the 2008 Wenchuan M_S 8.0 earthquake and 2013 Lushan M_S 7.0 earthquake occurred, provides an opportunity for us to study this important issue. Based on the GPS observations, we exploit the deformation response of the Southern Segment of the Longmenshan Fault (SSLMF) to the Wenchuan earthquake. The results are as follows: (1) during the co-seismic and post-seismic processes of the Wenchuan earthquake, the deformation is dominated by a continuous pattern in the SSLMF, which is different from the rupture pattern in the middle-northern segment of the Longmenshan Fault (LMF). Quantitatively, the compressive strain present between 2008 and 2013 was equal to the strain accumulation of 69 years during the interseismic period in the SSLMF. If the statistics scope is restricted to the eastern region of the Anxian-Guanxian Fault (AGF), which covers the Lushan source area (Abbr.: Eastern Region), the value is about 25 years; (2) After the Wenchuan earthquake, the strain accumulation pattern changes significantly. First, the deformation adjustment (especially the shear deformation) in the region that crosses the Maoxian-Wenchuan Fault (MWF) and Beichuan-Yingxiu Fault (BYF) (Abbr.: Western Region) is significantly greater than that in the Eastern Region. Furthermore, the crustal shortening is significant in the Eastern Region with minor adjustments in shear deformation. Second, the azimuth angles of the principal compressive strain rate in both regions show significant adjustments, which change fast in the first year of the observation period and then turn into the stable state. In general, the deformation responses of the SSLMF reveal that the Wenchuan earthquake promotes the occurrence of the Lushan earthquake. Their differences in the spatiotemporal domain can be attributed to the influence of afterslip, viscous relaxation of the lithosphere, mechanical parameters and block movement.