Different earthquake patterns for two neighboring fault segments within the Haiyuan Fault zone

Characteristic slip and characteristic earthquake models have been proposed for several decades. Such models have been supported recently by high-resolution offset measurements. These models suggest that slip along a fault recurs via similarly sized, large earthquakes. The inter-event strain accumulation rate(ratio of earthquake slip and preceding interseismic time period) is used here to test the characteristic earthquake model by linking the slip and timing of past earthquakes on the Haiyuan Fault. We address how the inter-event strain accumulation rate varies over multiple seismic cycles by combining paleoearthquake studies with high-resolution airborne light detection and ranging(Li DAR) data to document the timing and size of paleoearthquake displacements along the western and middle segments of the Haiyuan Fault. Our observations encompass 5 earthquake cycles. We find significant variations over time and space along the Haiyuan Fault. We observe that on the middle segment of the Haiyuan Fault the rates slow down or increase as an anticorrelated function of the rates of preceding earthquakes. Here, we propose that the inter-event strain accumulation rates on the middle segment of the Haiyuan Fault are oscillating both spatially and temporally. However, along the western segment, the inter-event strain accumulation rate is both spatially and temporally steady, which is in agreement with quasi-periodic and slip-predictable models. Finally,we propose that different fault segments within a single fault zone may behave according to different earthquake models.

The effect of altimetry data in estimating the elastic thickness of the lithosphere in the western Pacific Ocean

The elastic thickness of the lithosphere(Te)is a key parameter used to describe the strength of the lithosphere.It is usually estimated by a spectral analysis between gravity and topography.In previous research on the estimation of Te,altimetry data were used on both the gravity data and topography data,which could lead to deviations.The study described in this paper analyzed the effects of using gravity anomalies derived from different data sources on the estimation of Te,Taking the western Pacific region as an example,this study analyzed the impact of the repeated presence of altimetry satellite data on the calculation of the effective elastic thickness and found that if gravity anomalies and topography model both contain altimetry satellite data,they systematically overestimate effective elasticity.For a uniform area,the difference in Te can reach up to 30%.For a Te distribution,the difference can reach up to about16%.After eliminating this effect,the effective elastic thickness of the western Pacific region was found to be 10 km,and the statistical results of the effective elastic thickness distribution showed that the effective elastic thickness of the lithosphere in most areas of the western Pacific is about 12 km.The paper shows the importance of choosing the appropriate gravity model in evaluating the elastic thickness of lithosphere in the oceans.A figure of Te at seamounts with loading ages demonstrates that Te in the western Pacific is generally distributed within the 100-300℃isotherm depth and does not increase with loading age.

柴达木盆地新生代地层年代框架与沉积-构造演化

柴达木盆地的新生代地层非常发育,保存了从新生代早期至第四纪之间连续、完整的沉积记录.更为重要的是,柴达木盆地中发育丰富的新生代动、植物化石,为利用磁性地层学与古生物地层学方法建立盆地尺度的新生代地层年代框架,揭示盆地沉积演化、构造变形,以及青藏高原隆升、扩展的过程和动力学机制提供了重要的年代学制约.然而,目前关于柴达木盆地新生代地层层序和地层时代的认识还存在诸多矛盾之处。本文在野外观测、测量的基础上,总结、分析了柴达木盆地近年发表的相对连续、完整(厚度≥4500m)的磁性地层剖面,厘定了柴达木盆地新生代各岩石地层单元的地质年代.在此基础上,我们发现柴达木盆地西缘可能自始新世开始沉积,中部自渐新世(约31Ma)开始沉积,晚渐新世-早中新世沉积范围扩大至盆地东部柴达木盆地大部分地区自渐新世(31~26Ma)开始沉降,接受沉积的现象表明,青藏高原东北缘受印度板块与欧亚板块碰撞的影响开始发生构造变形.中中新世(约15Ma)以来,柴达木盆地沉积速率显著增加,盆地周缘山脉强烈隆升,揭示印度板块与欧亚板块持续汇聚作用导致的地壳缩短开始主宰高原东北部的构造变形,使柴达木盆地及其周缘造山带成为青藏高原向东北方向扩展过程中最新的组成部分.

深化大陆强震机理与预测研究

2021年5月12~13日,香山科学会议第700次学术讨论会召开,主题为“大陆型强震孕育发生的物理机制及地震预测探索”.会议包括3个中心议题.(1)地震预测预报研究的学术高地:强震孕育发生的大陆活动地块动力学模型;(2)新科技条件下的震源物理研究:大陆型强震孕育的区域动力学环境;(3)面向现代化目标的地震预测:多学科交叉创新,最大限度减轻地震灾害风险.

Colluvial wedges associated with pre-historical reverse faulting paleoearthquakes

Colluvial wedges collapsed from fault scarp can also be used to study reverse faulting paleoearthquakes. Generating processes of reverse faulting colluvial wedges are much more complex than those associated with normal faulting earthquakes. Reverse faulting colluvial wedge is also in triangle shape, and dies away from the fault. Contact between the fault and the colluvial wedge may be a simple straight reverse fault or a combination of an erosive surface in the upper part and a reverse fault in the lower part. Contents and grain sizes increase near the fault and along the base of a colluvial wedge. Based on examples from the piedmont reverse fault and fold along the northern Tainshan, we studied characteristics of reverse faulting colluvial wedges, and discussed the generating processes of reverse faulting colluvial wedges. Reverse faulting generates an unstable scarp hanging in the air immediately after an earthquake. Fallen material deposits along the base of newly formed fault scarp. Erosive

Drainage Responses to the Activity of the Langshan Range-Front Fault and Tectonic Implications

Langshan, a monoclinic mountain, which started to uplift since Oligocene, bounds the northwest margin of the Hetao Basin. The continuous activity of the active normal Langshan rangefront fault forms the typical basin-and-range landform in Langshan area and controls the landform evolution of Langshan. Langshan is an ideal place to study relationship between quantitative geomorphological index and active deformation. According to study on knickpoints, fitting on longitudinal channel profiles and steepness index, we demonstrate that the main controlling factors on distribution of normalized steepness index of channels are not climate(precipitation), lithology, sediment flux, but tectonic factor, or the activity of Langshan range-front fault. The short channels in southeast flank, whose lengths are shorter than 16 km, may be still in the non-steady status. If not considering these short channels, the distribution of normalized steepness index along the Langshan range-front fault appears like M-shape pattern, while the normalized steepness index in the middle section is higher than those at both ends. This pattern is well consistent with geometrical segmentation model of the Langshan range-front fault. Combining previous active tectonic research on Langshan range-front fault, which demonstrates the Langshan range-front fault has been in the stage of linkup, we reasonably infer the Langshan range-front fault now is the result of linkup of both fault which continuously bilaterally extended independently. Our tectonic geomorphological study also supports the conclusion that the Langshan range-front fault has been in the stage of linkup. The formation of several knickpoints due to tectonic factor may have been caused by slip-rate variation because of linkup of both independent faults. Based on cognition above, we also proposed the geological and geomorphological evolutionary model of the Langshan range-front fault since Oligocene.

柴达木盆地路乐河剖面磁性地层年代及其构造变形

青藏高原东北缘的柴达木盆地发育巨厚的新生代地层.这些地层记录了印度与欧亚大陆碰撞以来青藏高原向东北方向扩展过程中的构造变形、地貌演化与气候变化等信息.通过高密度的样品采集、测试与分析,古地磁测年结果显示,柴达木盆地北缘新生代地层出露较为连续、完整的路乐河剖面(路乐河组层型剖面)沉积年龄为30.9~5.2 Ma.路乐河剖面沉积环境与沉积速率分析揭示盆地新生代以来经历了约31与15 Ma开始的两期显著的构造变形事件:渐新世的构造变形导致了柴达木盆地的形成;中中新世以来的强烈构造变形导致了柴达木盆地的变形与改造.

Tsunami hazard assessment in the South China Sea:A review of recent progress and research gaps

The South China Sea region is potentially threatened by tsunami hazards originated from multiple sources:the Manila subduction zone in the east,the Littoral Fault Zone(LFZ)in the north,numerous submarine landslides on the continental slopes and the volcanic islands in the Luzon Strait.Infrequent but potentially devastating tsunami hazard poses a great threat to the populous coastal region,fishery,oil and gas exploitation in the deep sea,etc.Here we review the recent progress in tsunami hazard assessment in the South China Sea region,focusing on two primary sources:submarine earthquakes and landslides.We sort and review the literature by the two commonly used approaches:deterministic and probabilistic tsunami hazard assessment for both source types.By simulating tsunamis generated by typical earthquakes originated from the Manila Trench,the LFZ and landslides in the continental slopes,we investigate their tsunamigenic mechanism and key tsunami characteristics in the South China Sea region.We point out the research gaps and highlight the key issues to be addressed in the future.

Cenozoic tectonic evolution of regional fault systems in the SE Tibetan Plateau

The SE Tibetan Plateau,tectonically situated in the eastern India-Eurasia oblique convergence zone,has experienced multiple stages of deformation since the Cenozoic.Three major tectonic boundaries—the Ailaoshan-Red River,ChongshanLincang-Inthanon,and Gaoligong-Mogok shear zones—delineate the first-order tectonic framework in this region.The most striking structural features in the block interiors are a series of NW-and NE-trending fault systems,such as the Dayingjiang,Longlin-Ruili,Nantinghe,Red River,Weixi-Qiaohou,and Lancang-Genma faults,which have conjugate geometric relationships.In this study,we review these structures’geometric and kinematic characteristics and deformation histories.A synthesis of existing geological observations,geomorphological analyses,and chronological data reveals three major Cenozoic tectonothermal events,including crustal shortening,strike-slip shearing,and kinematic reversal.The boundary structures controlled the tectonic extrusion of plateau material during the early Oligocene-early Miocene.In the mid-late Miocene,NW-and NE-trending fault systems mostly experienced diachronous slip-sense inversions.The onset and spatial trend of regional kinematic reversal are constrained by existing chronologic data.Together with geophysical and geodetic observations,the activity and geodynamic drivers of the major fault systems and regional deformation styles are explored,revealing that the SE Tibetan Plateau underwent a transition from discrete(lateral block extrusion)to diffuse deformation in the mid-late Miocene.The intracontinental crustal deformation and its coupling with dynamic processes at depth during the plateau growth are discussed in the context of the IndiaEurasia convergence.

Effects of Aerobic Exercise on Atherosclerotic Risk in Postmenopausal Women

Introduction To study the effects of aerobic exercise on lipid metabolism,endothelial function,and oxidative stress reaction in postmenopausal women,in order to prevent and control atherosclerosis.Methods Thirty-two women with natural menopause were randomly divided into an exercise group and a control group.Participants in the exercise group(n=16)took part in a 3-month aerobic training program according to their exercise pre-scription,while participants in the control group(n=16)maintained their usual lifestyles.Lipids,endothelial function,and oxidative stress-related indicators were measured before and after the intervention.Results After 3 months of aerobic training at an intensity of 50-60%of cardiorespiratory fitness,serum total cholesterol and low-density lipoprotein cholesterol decreased significantly(P<0.05),and high-density lipoprotein cholesterol increased significantly(P<0.01).A significant reduction in endothelin(P<0.01)and a significant increase in nitric oxide(P<0.05)were also observed.The training intervention also delayed the increase in homocysteine and cysteine aspartate-specific protease-3 in postmenopausal women.Conclusions Aerobic exercise had a positive effect on blood lipids,endothelial function,and oxidative stress of postmeno-pausal women,and these changes may mitigate the risk of atherosclerosis occurrence.Similar exercise programs could be used as a primary atherosclerosis prevention strategy for postmenopausal women.