Rapid Identification and Emergency Investigation of Surface Ruptures and Geohazards Induced by the M_s 7.1 Yushu Earthquake

The rapid identification based on InSAR technology was proved to be effective in our emergency investigation of surface ruptures and geohazards induced by the Yushu earthquake.The earthquake-generating fault of the Yushu earthquake is the Yushu section of the Garze-Yushu faults zone.It strikes NWW-NW,23 km long near the Yushu County seat,dominated by left-lateral strike slip,and appearing as a surface rupture zone.The macroscopic epicenter is positioned at Guo-yang-yan -song-duo of Gyegu Town（33°03＇11＂N,96°51＇26＂E）,where the co-seismic horizontal offset measured is 1.75 m.Geohazards induced by the Yushu earthquake are mainly rockfalls,landslides,debris flows, and unstable slopes.They are controlled by the earthquake-generating fault and are mostly distributed along it.There are several geohazard chains having been established,such as earthquake,canal damage,soil liquefying,landslide-debris flow,earthquake,soil liquefying,roadbed deformation,etc.In order to prevent seismic hazards,generally,where there is a visible surface rupture induced by the Yushu earthquake,reconstruction should be at least beyond 20 m,on each side,from it.Sufficient attention should also be given to potential geohazards or geohazard chains induced by the earthquake.

Seismic relocation,focal mechanism and crustal seismic anisotropy associated with the 2010 Yushu M_S7.1 earthquake and its aftershocks

The 2010 Yushu MsT.1 earthquake occurred in Ganzi-Yushu fault, which is the south boundary of Bayan Har block. In this study, by using double difference algorithm, the locations of mainshock （33.13°N, 96.59°E, focal depth 10.22 km） and more than 600 aftershocks were obtained. The focal mechanisms of the mainshock and some aftershocks with Ms〉3.5 were estimated by jointly using broadband velocity waveforms from Global Seismic Network （GSN） and Qinghai Seismic Network as well. The focal mechanisms and relocation show that the strike of the fault plane is about 125° （WNW-ESE）, and the mainshock is left-laterally strikeslip. The parameters of shear-wave splitting were obtained at seismic stations of YUS and L6304 by systematic analysis method of shear-wave splitting （SAM） method. Based on the parameters of shear-wave splitting and focal mechanism, the characteristics of stress field in seismic source zone were analyzed. The directions of polarization at stations YUS and L6304 are different. It is concluded that after the mainshock and the Ms6.3 aftershock on April 14, the stress-field was changed.

Rb-Sr and Sm-Nd Isochron Ages of the Dongmozhazhua and Mohailaheng Pb-Zn Ore Deposits in the Yushu area, southern Qinghai and Their Geological Implications

Located on the northeast margin of the Qiangtang terrane between the Jinshajiang suture zone and Bangonghu-Nujiang suture zone,the Dongmozhazhua and Mohailaheng Pb-Zn deposits in the Yushu area of Qinghai Province are representative Pb-Zn deposits of the Pb-Zn-Cu polymetallic mineralization belt in the northern part of the Nujiang-Lancangjiang-Jinshajiang area,which are in the front belt of the Yushu thrust nappe system.The formed environments of these two deposits are different from those of sediment-hosted base metal deposits elsewhere in the world.The authors hold that they were formed during the Indian-Asian continental collision and developed within the fold-thrust belt combined with thrust and strike-slip-related Cenozoic basins in the interior of the collisional zone.Studying on the metallogenic epochs of these two deposits is helpful to the understanding of ore-forming regularity of the regional Pb-Zn-Cu mineralization belt and also to the search for new deposits in this region.The age of the Dongmozhazhua deposit has been determined by the Rb-Sr isochron method for sphalerite residues,whereas the age of the Mohailaheng deposit has been determined by the Rb-Sr isochron method for sphalerite residues and the Sm-Nd isochron method for fluorite.The age of the Dongmozhazhua deposit is 35.0-±0.0 Ma （（87Sr/86Sr）0=0.708807） for sphalerite residues.The age of the Mohailaheng deposit is 32.2±0.4 Ma （（87Sr/86Sr）o=0.708514） for sphalerite residues and 31.8±0.3 Ma （（143Nd/144Nd）o=0.512362） for fluorite with an average of 32.0 Ma.Together with the regional geological setting during mineralization,a possible tectonic model for metallogeny of the Dongmozhazhua and Mohailaheng Pb-Zn deposits has been established.These two ages are close to the ages of the Pb-Zn deposits in the Lanping and Tuotuohe basins,indicating that it is possible that the narrow 1000-kilometer-long belt controlled by a thrust nappe system on the eastern and northern margins of the Tibetan plateau could be a giant Pb-Zn mineralized belt.

Modeling of co- and post-seismic surface deformation and gravity changes of M W 6.9 Yushu, Qinghai,earthquake

Based on the elastic dislocation theory, multilayered crustal model, and rupture model obtained by seismic waveform inversion, we calculated the coand post-seismic surface deformation and gravity changes caused by the Yushu M W 6.9 earthquake occurred on April 14, 2010. The observed GPS velocity field and gravity field in Yushu areas are disturbed by the coand post-seismic effects induced by Yushu earthquake, thus the theoretical coand post-seismic deformation and gravity changes will provide important modification for the background tectonic movement of Yushu and surrounding regions. The time relaxation results show that the influences of Yushu earthquake on Yushu and surrounding areas will last as long as 30 to 50 years. The maximum horizontal displacement, vertical uplift and settlement are about 1.96, 0.27 and 0.16 m, respectively, the maximal positive and negative value of gravity changes are 8.892×10-7 m·s-2 and -4.861×10-7 m·s-2 , respectively. Significant spatial variations can be found on the coand post-seismic effects： The co-seismic effect mainly concentrates in the region near the rupture fault, while viscoelastic relaxation mostly acts on the far field. Therefore, when using the geodetic data to research tectonic motion, we should not only consider the effect of co-seismic caused by earthquake, but also pay attention to the effect of viscoelastic relaxation.

Gravity changes before and after the 2010 Ms7.1 Yushu earthquake

Absolute and relative gravity observations from 1998 -2010 from the China Crustal Movement Ob- servation Network, a major national scientific project, have been used to model the gravity field and its varia- tions associated with the April 14, 2010 Ms7.1 Yushu earthquake. The evolution of the regional gravity field and its relationship with seismicity before and after the Yushu earthquake are studied. The observed gravity changes are closely related to the active Ganzi-Yushu Fault, and gravity measurements can be used to observe the migration of material accompanying active faults and crustal tectonics. The dynamic variation of the gravity field reflects its evolution prior to and during the Yushu earthquake. The gravity measurements near its epicen- ter are as large as 80 × 10-s m/s2.and they show wave-like increases with time prior to the Yushu earth- quake.

Estimating Moho basement and faults using gravity inversion in Yushu-earthquake area,China

A gravity survey was conducted one month after the 2010 Yushu earthquake in the epicenter area. The cross-fauh survey line was 500 km long, from Langqian county to Qingshuihe county, in a transition zone between Bayan Har block and Qiangtang block, in an area of high elevation, large undulating terrain, and complex geological features. An interpretation of the data was carried out together with other kinds of data, such as seismic exploration and magnetic exploration. The result shows that gravity is sensitive to fault bounda- ry ; the geologic structure of the region is complex at middle and upper depths, and the density profile reveals an eastward-pushing fault movement.

Deformation of the Most Recent Co-seismic Surface Ruptures Along the Garzê–Yushu Fault Zone(Dangjiang Segment)and Tectonic Implications For the Tibetan Plateau

The Garzê–Yushu strike-slip fault in central Tibet is the locus of strong earthquakes（M 〉 7）. The deformation and geometry of the co-seismic surface ruptures are reflected in the surface morphology of the fault and depend on the structure of the upper crust as well as the pre-existing tectonics. Therefore, the most recent co-seismic surface ruptures along the Garzê–Yushu fault zone（Dangjiang segment） reveal the surface deformation of the central Tibetan Plateau. Remote sensing images and field investigations suggest a 85 km long surface rupture zone（striking NW-NWW）, less than 50 m wide, defined by discontinuous fault scarps, right-stepping en echelon tensional cracks and left-stepping mole tracks that point to a left-lateral strike-slip fault. The gullies that cross fault scarps record systematic left-lateral offsets of 1.8 m to 5.0 m owing to the most recent earthquake, with moment magnitude of about M 7.5, in the Dangjiang segment. Geological and geomorphological features suggest that the spatial distribution of the 1738 co-seismic surface rupture zone was controlled by the pre-existing active Garzê–Yushu fault zone（Dangjiang segment）. We confirm that the Garzê–Yushu fault zone, a boundary between the Bayan Har Block to the north and the Qiangtang Block to the south, accommodates the eastward extrusion of the Tibetan Plateau and generates strong earthquakes that release the strain energy owing to the relative motion between the Bayan Har and Qiangtang Blocks.

Risk Assessment of Secondary Geological Disasters Induced by the Yushu Earthquake

The Yushu Ms 7.1 earthquake occurred on April 14,2010 in Qinghai Province,China.It induced a mass of secondary geological disasters,such as collapses,landslides,and debris flows.Risk assessment maps are important for geological disaster prevention and mitigation,and also can serve as a guide for post-earthquake reconstruction.Firstly,a hazard assessment index system of secondary geological disasters in the earthquake region was built in this paper,which was based on detailed analysis of environmental and triggering factors closely related to geological disasters in the study area.GIS technology was utilized to extract and analyze the assessment index.Hazard assessment maps of secondary geological disasters were obtained by spatial modeling and overlaying analysis.Secondly,an analysis of the vulnerability of hazard bearing bodies in the area was conducted,important information,such as, population density,percentage of arable land, industrial and agricultural outputs per unit area were regarded as assessment indices to evaluate socioeconomic vulnerability.Thirdly,the risk level of secondary geological disasters of the area was obtained by the formula:Risk=Hazard×Vulnerability. Risk assessment maps were categorized into four levels,including"low","moderate","high"and"very high".These results show that some urban areas are at very high risk,including Jiegu,Chengwen,Xiaxiula and Sahuteng towns.This research can provide some references and suggestions to improve decisionmaking support for emergency relief and post- earthquake reconstruction in the study area.

A successful mountain rescue operation in Yushu Earthquake

On April 14, 2010, an earthquake reaching 7.1 Richter scale struck Jiegu Town of Yushu. More than 2 698 people were confirmed dead, and 12 135 were injured, of which 1 434 were severely injured. Rescue operation was carried out soon after the disaster; however, the rescue teams face great challenges of altitude hypoxia, freezing temperature and very bad weather. Thus, 1 434 severe injuries were rapidly transported airlifted to hospitals in Xining and neighboring provinces for effective treatment. The extremity trauma （49.9 % ） was the most common patteru of injuries. Asphyxia （40.8 % ） was by far the most important reason for death. A high incidence of acute altitude illness in the lowland rescuers was a special medical problem during the highest earthquake in Yushu. We have learned more lessons from Yushu Earthquake.

Medical mountain rescue in the Yushu Earthquake: Have lessons been learned?

On April 14,2010,an earthquake reaching Richter scale 7.1 struck Jiegu Town of Yushu,a mountain rescue operation promptly launched. All injurers had a direct assess to take medical care,and were immediately rescued and rapidly evacuated by air to Xining and Golmud at lower altitudes and admitted to advanced hospitals. Almost all of the injurers have been completely recovered. Yushu Earthquake was one of the highest earthquakes in the world,with a high incidence of acute altitude illness,which was observed in about 80 % of the lowland rescuers at an altitude of 4 000 m."Rescue the rescuers"became the major task of Qinghai-Tibetan rescue teams,all the severe patients were rapidly descended to Xining and treated promptly and effectively. The outcome was excellent,all patients survived. After the earthquake,it is a long and arduous task to reconstruct what has been destroyed. Medical teams continue to work in the Yushu Earthquake area because about 30 000 workers and carders are now here for rebuilding the earthquake center. Thus the prevention and treatment of altitude illness are still critical tasks for medical teams. Although all the fights are successful,there are more experiences and lessons we have learned from the medical mountain rescue during the earthquake and the reconstruction,and reports here are to sum up our experiences from the medical mountain rescue operation in Yushu Earthquake and draw the lessons that we should learn. With the increasing of earthquake probability occurring in the Qinghai-Tibetan Plateau,we also should prepare against earthquake disasters and for further rescue training in the high mountains.

Fast inversion of rupture process of the 14 April 2010 Yushu,Qinghai,earthquake

Four results of the rupture process of 14 April 2010 Yushu, Qinghai, earthquake, obtained by inverting the broadband seismic data of Global Seismographic Network （GSN） based on the inversion method of earthquake rupture process, were compared and discussed. It is found that the Yushu earthquake has several basic characteristics as follows： 1 There exist two principal sub-events which correspond to two slip-concentrated patches being located near the hypocenter and to the southeast of the epicenter. The rupture of the slip-concentrated patch to the southeast of the epicenter broke though the ground surface; 2 The peak slip and peak slip-rate are about 2.1 m and 1.1 m/s, respectively, indicating that the Yushu earthquake is an event with large slip-rate on the fault plane; 3 Overall the Yushu earthquake is a unilateral rupture event with the rupture mainly propagating southeastward. The strong focusing of the seismic energy in the southeast of the epicenter due to the ＂seismic Doppler effect＂ reasonably accounts for the tremendous damage in the Yushu city.

Ascent schedules,acute altitude illness,and altitude acclimatization:Observations on the Yushu Earthquake

During the Yushu Earthquake on April 14,2010,a large number of rescuers from sea level or lowlands ascended to the quake areas very rapidly or rapidly less than 24 h. However,Yushu Earthquake is the highest quake in the world at altitudes between 3 750 m and 4 878 m where is a serious hypoxic environment. A high incidence of acute altitude illness was found in the unacclimatized rescuers;the mountain rescue operation changed as "rescue the rescuers". Lesson from the Yushu Earthquake is that the occurrence of acute altitude illness may be closely related to the ascent schedules. This prompted us to study the relationship between ascent rate and the incidence and severity of acute altitude illness;five different groups were compared. The first group was 42 sea level male young soldiers who ascended to quake area very rapidly within 8 h at 4 000 m;the second group was 48 sea level male young soldiers who ascended to 4 000 m rapidly less than 18 h;the third group was 66 acclimatized medical workers from 2 261 m who ascended to 4 000 m rapidly within 12 h;the fourth group was 56 Tibetan medical workers from 2 800 m who ascended to 4 000 m rapidly within 8 h;the fifth group was 50 male sea level workers who ascended to 4 000 m gradually over a period of 4 d. The results showed that the sea level rescuers ascended to 4 000 m very rapidly or rapidly had the highest incidence of acute mountain sickness (AMS) with the greatest AMS scores and the lowest arterial oxygen saturation (SaO2);the sea level workers ascended to 4 000 m gradually had moderate incidence of AMS with moderate AMS scores and SaO2 values;whereas the acclimatized and adapted rescuers had the lowest incidence of AMS,lowest AMS scores and higher SaO2;especially none AMS occurred in Tibetan rescuers. AMS score is inversely related to the ascent rate (r=-0.24,p< 0.001). Additionally,acute altitude illness is significantly influenced by altitude acclimatization. The ascent rate is inversely re- lated to the period of altitude acclimatization whereas the time of perfect recovered from AMS is positively correlated to the time taken to acclimatize. Generally,the best means of preventing acute altitude illness is slow and gradual ascent to high altitude,as this allows time for establishing altitude acclimatization and tolerance to the hypoxic environment. However,during an emergency circumstance,such as mountain rescue operation,the rescuers must rapidly ascend to high altitude,so a series of preventive strategies including pre-acclimatization,using some prophylactic drugs and oxygen supplementary are sorely necessary.

Post-earthquake building damage assessment in Yushu using airborne SAR imagery

The synthetic aperture radar （SAR） plays an important role in earthquake emergency response because of its all-time and all-weather imaging capabilities. On April 14, 2010, an Ms7.1 earthquake occurred in Yushu county, Qinghai province of China, causing a lot of buildings collapsed. In this paper, the building damage in Yushu city due to the earthquake was assessed quantitatively using high-resolution X-band airborne SAR image. The features of the buildings with different damage levels （collapsed, partial collapsed, non-collapsed） in the SAR image were analyzed first. Based on these building features, we interpreted the individual building damage in Yushu city block by block and got the numbers of the collapsed, partial collapsed and non-collapsed buildings separately for each block, referring to pre-earthquake QuickBird image when necessary. Let the damage index of individual collapsed, partial collapsed, non-collapsed building be 1, 0.5, 0 respectively, the remote sensing damage index of each block was then calculated through remote sensing damage index equation. Finally, the preliminary quantitative relationship between the remote sensing damage index interpreted from the SAR image and that interpreted from the optical image was built up. It can be concluded that a desirable damage assessment result can be derived from high-resolution airborne SAR imagery.

Co-seismic deformation of the 2010 Mw6. 9 Yushu earthquake from InSAR images

Co-seismic ground-surface deformation of the Yushu earthquake on April 14, 2010 is studied on the basis of interferometry principle by using InSAR images from ALOS PALSAR and ENVISAT ASAR pairs. The observed maximum line-of-sight displacement is 54 cm, which is equivalent to a sinistral strike slip of 180 cm on the surface. The location of macro-epicenter is very close to the epicenter determined by in situ investigation, suggesting that InSAR is an ideal tool for quick identification of the macro-epicenter, and thus for timely disaster assessment after a destructive earthquake.

A necklace of pearl in high altitude medicine and hypoxic physiology in Yushu Earthquake

During Yushu Earthquake,a large number of rescuers flocked to the mountainous quake areas. Under such a very specific circumstance,a high incidence of acute altitude illness was observed in rescuers who rapidly traveled from near sea level to an altitude of 4 000 m. It is evident that acute altitude illness leads to a significant human and economic toll,and also seriously influences the mountain rescue operation. So what does this teach us about mountain rescue in Yushu? Professor Wu Tianyi and many other authors collected shining points of the experiences and drew the lessons from the Yushu Earthquake into this special issue in Engineering Sciences which is like to thread pearl beads for a necklace. What readers learn from this special issue will have implications for the health and well-being of all high altitude populations all over the world.

Subclinical high altitude pulmonary edema: A clinical observation of 12 cases in Yushu

During the Yushu Earthquake on April 14,2010,a high incidence of acute high altitude illness was observed in the mountain rescuers,and 0.73 % of these patients suffered from high altitude pulmonary edema,of which 12 patients developed subclinical pulmonary edema and concomitantly contracted acute mountain sickness. Symptoms and signs were atypically high heart rate with high respiratory rate,striking cyanosis,and significantly low oxygen saturation,whereas no moist rates were heard on auscultation,and Chest X-ray showed peripheral with a patchy distribution of mottled infiltrations in one or both lung fields. We believe that subclinical high altitude pulmonary edema is an earliest stage of pulmonary edema at high altitude. The possible pathogenesis and the diagnosis were discussed.

Joint inversion of gravity and seismic data along a profile across the seismogenic fault of 2010 Yushu Ms7. 1 earthquake

Yushu Ms7.1 earthquake occurred on the Ganzi-Yushu fault zone, across which we carried out a joint relative-gravity and seismic-reflection survey, and then performed a gravity inversion constrained by the seismic-reflection result. Based on the data of complete Bouguer gravity anomaly and seismic reflection, we obtained a layered interface structure in deep crust down to Moho. Our study showed that the inversion could reveal the interfaces of strata along the survey profile and the directions of regional faults in two-dimension. From the characteristics of the observed topography of the Moho basement, we tentatively confirmed that the uplift of eastern edge of Qinghai-Tibet plateau was caused by the subduetion of the Indian plate.

Landslides and Slope Fissures Triggered by the April 14,2010 Yushu Earthquake, China

On April 14, 2010 at 07：49 （Beijing time）, a catastrophic earthquake with Ms 7. 1 occurred at the central Qinghai-Tibetan Plateau. The epicenter was located at Yushu county, Qinghai Province, China. A total of 2036 landslides were determined from visual interpretation of aerial photographs and high resolution remote sensing images, and verified by selected field investigations. These landslides covered a total area of about 1. 194km~. Characteristics and failure mechanisms of these landslides are listed in this paper, including the fact that the spatial distribution of these landslides is controlled by co- seismic main surface fault ruptures. Most of the landslides were small scale, causing rather less hazards, and often occurring close to each other. The landslides were of various types, including mainly disrupted landslides and rock falls in shallows and also deep-seated landslides, liquefaction induced landslides, and compound landslides. In addition to strong ground shaking, which is the direct landslide triggering factor, geological, topographical, and human activity also have impact on the occurrence of earthquake triggered landslides. In this paper, five types of failure mechanisms related to the landslides are presented, namely, the excavated toes of slopes accompanied by strong ground shaking; surface water infiltration accompanied by strong ground shaking; co- seismic fault slipping accompanied by strong ground shaking; only strong ground shaking; and delayed occurrence of landslides due to snow melt or rainfall infiltration at sites where slopes were weakened by co-seismic ground shaking. Besides the main co-seismic surface ruptures, slope fissures were also delineated from visual interpretation of aerial photographs in high resolution. A total of 4814 slope fissures, with a total length up to 77. lkm, were finally mapped. These slope fissures are mainly distributed on the slopes located at the southeastern end of the main co-seismic surface rupture zone, an area subject to strong compression during the earthquake.

Sleep quality alterations in healthy workers at high altitude in Yushu area

During the period of reconstruction after Yushu Earthquake, a large number of sea-level or lowland workers ascended there and worked at altitudes between 3 750 m and 4 878 m which is a hypoxic environment. To investigate the sleep quality at that altitude, we performed two full polysomnographies （PSGs） in 10 volunteers, who were healthy male workers, aged 31 ：i：6.6, born and living at sea level, without experience of pre-altitude expo- sure. The assessment of subjective sleep quality was performed twice in each volunteer. The first investigations were carried out at sea level in Jinan city （pB=760 torr, 1 torr=133.322 4 Pa）. The second studies were performed at an altitude of 3 750 m （pB=416 tort） in Yushu Jiegu in the same 10 workers after they lived and worked at that alti- tude for 5 months. At sea level, workers presented a normal sleep structure and a higher oxygenation during sleep. However, as compared to sea-level sleep, at 3 750 m, workers had a shorter total sleep time （TST） （p 〈 0.001）, a longer stage 1 non-rapid eye movement （nREM） sleep （p 〈 0.05） and a shorter 3＋4 nREM and rapid eye movement （REM） sleep （p 〈 0.05） with a severe sleep hypoxemia （p 〈 0.01）. Our data suggested that sea-level workers revealed a disturbed sleep and a bad sleep quality with a significant sleep hypoxemia at altitude of 3 750 m. Strengthening the prevention and treatment are thereby sorely necessary.

Imaging manifestations and the related clinical characteristics of chest trauma during the Yushu Earthquake

The purpose of this study was focused on the imaging features of the chest trauma and its relation to clinical characteristics. All the injured patients were from the Yushu Earthquake areas on days April 14 - 23,2010. After an initial treatment,the injurers were rapidly transported from Yushu at an altitude of 4 000 m via air to Xining at 2 260 m within 6~8 h,and promptly admitted to Qinghai Provincial People’s Hospital. A total of 130 wounded injurers who had high suspicion of chest injuries all had examinations of Chest X-ray and computed tomography(CT)images. Of them 63 injurers presented at least one of the features of the chest trauma in imaging with a positive rate of 48.5 %. Of these,37 cases (28.5 %) were multi-system with multiple injuries ,33 cases (25.4 %) were chest trauma with multi-injury types,which included thoracic fractures in 54 cases (85.7 %),pleural injury in 56 cases (88.9 %),lung injury in 54 cases (85.7 %),lungs complications in 37 cases (58.7 %),and extrapulmonary complications of 35 cases (55.6 %). The radiological data were analyzed retrospectively. The features of chest trauma in Yushu Earthquake,the complications of chest injuries,and the relation between imaging findings and clinical manifestations,as well as the differences of chest trauma between Yushu Earthquake and Wenchuan Earthquake were discussed in detail.