Jianping Wu

Aftershock Observation and Analysis of the 2013 Ms 7.0 Lushan Earthquake

Online Material: Figures of station deployment time and of spatial and temporal depiction of aftershocks, and tables of station information and aftershock catalogs.nnAt 08:02 (local and Beijing time) on 20 April 2013, an earthquake of M sxa07.0 ( M wxa06.6) struck Lushan County in Sichuan Province, southwestern China (hereafter referred to as the Lushan earthquake). The Lushan earthquake resulted in casualties and severe damage to the buildings and to the economic activities of the region. The earthquake left 193 dead, up to 10,000 injured, and 25 missing. The direct economic loss hit over

S wave velocity structure in southwest China from surface wave tomography and receiver functions

1.6 billion U.S.nnThe Lushan earthquake is the second destructive earthquake to have occurred in the southern segment of the Longmenshan fault zone since the 12 May 2008 M sxa08.0 Wenchuan earthquake (Fig.xa01). The distance between the epicenters of the Lushan earthquake and the Wenchuan earthquake is about 87xa0km (Fang, Wu, Wang, Lu, etxa0al. , 2013). As happened following the Wenchuan earthquake, the occurrence of the Lushan earthquake also stimulated lots of discussions on the seismic risk potential and prediction in southwest China. In particular, whether it was a large aftershock of the Wenchuan earthquake has been heatedly debated (Chen etxa0al. , 2013; Du etxa0al. , 2013; J. Liu etxa0al. , 2013; Wang etxa0al. , 2013; Jia etxa0al. , 2014).nnnnFigure 1. n(a)xa0Tectonic settings of the Longmenshan fault zone. Red and yellow stars indicate the epicenters of the Wenchuan and Lushan earthquakes, respectively. The focal mechanisms of the Lushan earthquake and Wenchuan earthquake are also shown. Red circles represent aftershocks of the Lushan and Wenchuan earthquakes. Black lines indicate the main faults. The inset map shows the location of the study region in the Chinese mainland. (b)xa0The distribution of seismic stations in and around the epicentral region of the Lushan …

Complex Structure beneath the Southeastern Tibetan Plateau from Teleseismic P‐Wave Tomography

Using the surface wave records of 504 teleseismic events at 50 temporary and 92 permanent seismic stations in southwest China, we obtain phase velocity maps at 10, 15, 25, 40, 60, and 75 s at a grid spacing of 0.5° × 0.5° from the interstation correlation method and surface wave tomography. We also obtain the S wave velocity structures beneath three profiles using the joint inversion of receiver functions and surface waves. At short periods (10 and 15 s), high-velocity zones (HVZs) are found in the Panzhihua-Emeishan region, the Sichuan basin and the Weixi-Lijiang region surrounding the low-velocity zones (LVZs) from Songpan-Ganzi block to the east of Lijiang, where the elevations are significantly higher. At long periods (40, 60, and 75 s), HVZs are found in the Weixi-Lijiang region, the Panzhihua-Chuxiong basin,and the Kunming-Tonghai region, which form a belt in the center part of the study area. The fast polarization directions on both sides of the belt defined by the shear wave splitting of teleseismic SKS waves vary significantly and indicate that the flow of material from the plateau is blocked in two different depth intervals and leads to different horizontal extents. The long-period maps and the structures along the three profiles show that LVZs are present in the upper mantle beneath rapidly slipping fault zones, such as the Anninghe-Zemuhe-Xiaojiang fault zone, the Red River fault zone, and the Xiaojinhe fault zone, implying that these faults penetrate deep into the mantle.

Relocation of the 2012 M s 6.6 Xinjiang Xinyuan earthquake sequence

Abstract A high‐resolution image of the deep structures in the southeastern Tibetan plateau and Yangtze block was revealed by teleseismic inversion based on the dense teleseismic data collected from the permanent seismic stations and a recently deployed temporary seismic array. The results show that low‐velocity anomaly is imaged mainly in the eastern and southeastern Tibetan plateau (except the southern Panzhihua area) above 200xa0km depth in the upper mantle, whereas a high‐velocity anomaly exists to its east especially beneath the Sichuan basin. We infer the cold crustal and upper mantle of the Sichuan basin prevents the extrusion of mantle materials of the Tibetan plateau, while the cold lithosphere of the western Yangtze block is eroded by the upper‐mantle materials with high temperature from the extrusion of the Tibetan plateau. Under the Tengchong volcanic region, a low‐velocity anomaly extends to 300xa0km depth. A high‐velocity anomaly is shown beneath the region from the southern Sichuan to Yunnan in the mantle transition zone, and the anomaly reaches deeper to the lower mantle in the western Yunnan area. The widespread low velocity above the high velocity in the Yunnan region indicates the dehydration of the Indian plate may occur in the mantle transition zone, which causes fast‐rising heat and lower melting temperature in the upper mantle. A small‐scale, high‐velocity anomaly in the southern Panzhihua region is probably related to the late Paleozoic mantle plume activity. It plays an important role in impeding the southward extrusion of the plateau materials, which might be one of the causes for the rapid change of the polarization direction of the fast shear waves around the area.

Relocation of the Yushu M S 7.1 earthquake and its aftershocks in 2010 from HypoDD

At 05:07 AM on June 30, 2012 (Beijing time), an Ms6.6 earthquake (hereafter referred to as Xinyuan earthquake) occurred at the junction of Xinyuan County, Ili Kazak Autonomous Prefecture and Hejing County, Bayinguoleng Mongol Autonomous Prefecture in Xinjiang Uygur Autonomous Region. The location of the main shock determined by China Earthquake Network Center is 43.4°N, 84.8°E and focal depth is 7 km. By the end of 08:00 AM on July 23, 501 aftershocks were recorded, of which 9 aftershocks with magnitude larger than ML4.0, and the largest magnitude of the aftershocks is ML4.9. The earthquake affected a large area, such as Yili, Urumqi, Shihezi, Karamay and so on. According to the statistics from Department of Civil Affairs, Xinjiang Uygur Autonomous Region, 155 thousand people were affected, with a direct economic loss of nearly 2 billion yuan (RMB). Xinyuan earthquake occurred in the northern Tianshan fault zone near the Kashi River fault. Seismic activity in the Kashi River fault is strong. More than three earthquakes with magnitude larger than 7 in the past 200 years have occurred near the Kashi River fault. These strong earthquakes are March 8, 1812 Nilka M8.0 earthquake, December 23, 1906 Manas M7.7 earthquake, March 10, 1944 Xinyuan M7.2 earthquake (Figure 1). We quickly relocated the aftershock sequences after the earthquake. Our new results provide important reference information for the study of seismogenic structure, the analysis of the spatial and temporal characteristics of the aftershock activity, and the determination of aftershock activity trend.

Crustal thickness and Poisson's ratio in southwest China based on data from dense seismic arrays

After the Yushu MS7.1 earthquake on April 14, 2010, a large number of aftershocks were recorded by the surrounding permanent network and temporary seismic stations. Due to the distribution of stations, knowledge about velocity structure, the reliability of seismic phases, and so on, the location result from conventional method is usually of low precision, from which it is difficult to recognize the spatial and temporal distribution and the trends of aftershock activity. In this paper, by using teleseismic waveforms recorded by permanent station, the seismic velocity structure beneath the vicinity is obtained from receiver function stacking and inversion methods. And the Yushu earthquake sequences are relocated from seismic phase data by HypoDD. The results show that the Yushu MS7.1 earthquake occurred at 13 km depth; the aftershock sequences were distributed mainly in the NWW along the Garzê-Yushu fault, and most aftershocks were concentrated in a 100 km length and 5–20 km depth. Combined with the velocity structure, it can be inferred that the earthquake mainly destroys the high-velocity layer of the upper crust. In the west of the seismic fault near (33.3°N, 96.2°E), the aftershock sequences were distributed like a straight column, suggesting there was a comminuted break from 25km depth to the ground.

Relocation of the mainshock and aftershock sequences of M S 7.0 Sichuan Lushan earthquake

Crustal thickness and Poissons ratio are important parameters to characterize regional isostasy state and material composition or state. Using the teleseismic waveform data from 141 permanent stations and 785 temporary stations in southwest China, we obtain the crustal thickness and average Poissons ratio by the H-κ stacking of receiver functions. In the west (the SE Tibetan plateau and the Yunnan-Burma-Thailand block) and southeast (the Cathaysian block and southern Yangtze craton) of the study region, there are high correlation coefficients for the crustal thicknesses between what we obtain from the receiver functions and what we calculate from the Airy isostasy model, indicating that a state of isostasy can be achieved at the crust-mantle boundary beneath these two regions. In the northeast (northern Yangtze craton), the correlation coefficient is lower, indicating that the effect of the lithosphere needs to be considered for a regional isostasy. Intermediate Poissons ratios (0.26≤σ≤0.28) are found beneath the northern Panzhihua-Emeishan region. Combing the high velocity features from previous study, we speculate that it may be related to the Emeishan large igneous province. High Poissons ratios (σ>0.28)- are found beneath the SE Tibetan plateau and the nearby strike-slip faults, such as the Anninghe-Zemuhe fault and the northern Xiaojiang fault. Combing the low velocity zones from previous study, we speculate that there may be partially melted and lower crustal flow.