China Earthquake Administration

Research Article| September 01, 2004 Continuous deformation of the Tibetan Plateau from global positioning system data Pei-Zhen Zhang; Pei-Zhen Zhang 1State Key Laboratory of Earthquake Dynamics, Institute of Geology, Chinese Earthquake Administration, Beijing 100029, China, and State Key Laboratory of Loess and Quaternary Geology, IEE, CAS, Xi'an, China Search for other works by this author on: GSW Google Scholar Zhengkang Shen; Zhengkang Shen 2State Key Laboratory of Earthquake Dynamics, Institute of Geology, Chinese Earthquake Administration, Beijing 100029, China, and Department of Earth and Space Sciences, University of California, Los Angeles, California 90024, USA Search for other works by this author on: GSW Google Scholar Min Wang; Min Wang 3State Key Laboratory of Earthquake Dynamics, Institute of Geology, Chinese Earthquake Administration, Beijing 100029, China Search for other works by this author on: GSW Google Scholar Weijun Gan; Weijun Gan 3State Key Laboratory of Earthquake Dynamics, Institute of Geology, Chinese Earthquake Administration, Beijing 100029, China Search for other works by this author on: GSW Google Scholar Roland Bürgmann; Roland Bürgmann 4Department of Earth and Planetary Science, University of California, Berkeley, California 94720, USA Search for other works by this author on: GSW Google Scholar Peter Molnar; Peter Molnar 5Department of Geological Sciences, and Cooperative Institute for Research in Environmental Sciences, University of Colorado, Boulder, Colorado 80309, USA Search for other works by this author on: GSW Google Scholar Qi Wang; Qi Wang 6Institute of Seismology, Chinese Earthquake Administration, Wuhan 430071, China Search for other works by this author on: GSW Google Scholar Zhijun Niu; Zhijun Niu 7National Earthquake Infrastructure Service, Chinese Earthquake Administration, Beijing 100081, China Search for other works by this author on: GSW Google Scholar Jianzhong Sun; Jianzhong Sun 7National Earthquake Infrastructure Service, Chinese Earthquake Administration, Beijing 100081, China Search for other works by this author on: GSW Google Scholar Jianchun Wu; Jianchun Wu 7National Earthquake Infrastructure Service, Chinese Earthquake Administration, Beijing 100081, China Search for other works by this author on: GSW Google Scholar Sun Hanrong; Sun Hanrong 7National Earthquake Infrastructure Service, Chinese Earthquake Administration, Beijing 100081, China Search for other works by this author on: GSW Google Scholar You Xinzhao You Xinzhao 7National Earthquake Infrastructure Service, Chinese Earthquake Administration, Beijing 100081, China Search for other works by this author on: GSW Google Scholar Author and Article Information Pei-Zhen Zhang 1State Key Laboratory of Earthquake Dynamics, Institute of Geology, Chinese Earthquake Administration, Beijing 100029, China, and State Key Laboratory of Loess and Quaternary Geology, IEE, CAS, Xi'an, China Zhengkang Shen 2State Key Laboratory of Earthquake Dynamics, Institute of Geology, Chinese Earthquake Administration, Beijing 100029, China, and Department of Earth and Space Sciences, University of California, Los Angeles, California 90024, USA Min Wang 3State Key Laboratory of Earthquake Dynamics, Institute of Geology, Chinese Earthquake Administration, Beijing 100029, China Weijun Gan 3State Key Laboratory of Earthquake Dynamics, Institute of Geology, Chinese Earthquake Administration, Beijing 100029, China Roland Bürgmann 4Department of Earth and Planetary Science, University of California, Berkeley, California 94720, USA Peter Molnar 5Department of Geological Sciences, and Cooperative Institute for Research in Environmental Sciences, University of Colorado, Boulder, Colorado 80309, USA Qi Wang 6Institute of Seismology, Chinese Earthquake Administration, Wuhan 430071, China Zhijun Niu 7National Earthquake Infrastructure Service, Chinese Earthquake Administration, Beijing 100081, China Jianzhong Sun 7National Earthquake Infrastructure Service, Chinese Earthquake Administration, Beijing 100081, China Jianchun Wu 7National Earthquake Infrastructure Service, Chinese Earthquake Administration, Beijing 100081, China Sun Hanrong 7National Earthquake Infrastructure Service, Chinese Earthquake Administration, Beijing 100081, China You Xinzhao 7National Earthquake Infrastructure Service, Chinese Earthquake Administration, Beijing 100081, China Publisher: Geological Society of America Received: 12 Feb 2004 Revision Received: 06 May 2004 Accepted: 10 May 2004 First Online: 03 Mar 2017 Online ISSN: 1943-2682 Print ISSN: 0091-7613 Geological Society of America Geology (2004) 32 (9): 809–812. https://doi.org/10.1130/G20554.1 Article history Received: 12 Feb 2004 Revision Received: 06 May 2004 Accepted: 10 May 2004 First Online: 03 Mar 2017 Cite View This Citation Add to Citation Manager Share Icon Share Facebook Twitter LinkedIn MailTo Tools Icon Tools Get Permissions Search Site Citation Pei-Zhen Zhang, Zhengkang Shen, Min Wang, Weijun Gan, Roland Bürgmann, Peter Molnar, Qi Wang, Zhijun Niu, Jianzhong Sun, Jianchun Wu, Sun Hanrong, You Xinzhao; Continuous deformation of the Tibetan Plateau from global positioning system data. Geology 2004;; 32 (9): 809–812. doi: https://doi.org/10.1130/G20554.1 Download citation file: Ris (Zotero) Refmanager EasyBib Bookends Mendeley Papers EndNote RefWorks BibTex toolbar search Search Dropdown Menu toolbar search search input Search input auto suggest filter your search All ContentBy SocietyGeology Search Advanced Search Abstract Global positioning system velocities from 553 control points within the Tibetan Plateau and on its margins show that the present-day tectonics in the plateau is best described as deformation of a continuous medium, at least when averaged over distances of >∼100 km. Deformation occurs throughout the plateau interior by ESE-WNW extension and slightly slower NNE-SSW shortening. Relative to Eurasia, material within the plateau interior moves roughly eastward with speeds that increase toward the east, and then flows southward around the eastern end of the Himalaya. Crustal thickening on the northeastern and eastern margins of the plateau occurs over a zone ∼400 km wide and cannot be the result of elastic strain on a single major thrust fault. Shortening there accommodates much of India's penetration into Eurasia. A description in terms of movements of rigid blocks with elastic strain associated with slip on faults between them cannot match the velocity field. You do not have access to this content, please speak to your institutional administrator if you feel you should have access.

A high‐resolution P wave tomographic model of the crust and mantle down to 1100 km depth under China and surrounding regions is determined by using about one million arrival times of P, pP, PP, and PcP waves from 19,361 earthquakes recorded by 1012 seismic stations. The subducting Pacific slab is imaged clearly as a high‐velocity zone from the oceanic trenches down to about 600 km depth, and intermediate‐depth and deep earthquakes are located within the slab. The Pacific slab becomes stagnant in the mantle transition zone under east China. The western edge of the stagnant slab is roughly coincident with a surface topographic boundary in east China. The active Changbai and Wudalianchi intraplate volcanoes in northeast China are underlain by significant slow anomalies in the upper mantle, above the stagnant Pacific slab. These results suggest that the active intraplate volcanoes in NE China are not hot spots but a kind of back‐arc volcano associated with the deep subduction of the Pacific slab and its stagnancy in the transition zone. Under the Mariana arc, however, the Pacific slab penetrates directly down to the lower mantle. The active Tengchong volcano in southwest China is related to the eastward subduction of the Burma microplate. The subducting Indian and Philippine Sea plates are also imaged clearly. The Indian plate has subducted down to 200–300 km depth under the Tibetan Plateau with a horizontal moving distance of about 500 km. High‐velocity anomalies are revealed in the upper mantle under the Tarim basin, Ordos, and Sichuan basin, which are three stable blocks in China.

Abstract We process rigorously GPS data observed during the past 25 years from continental China to derive site secular velocities. Analysis of the velocity solution leads to the following results. (a) The deformation field inside the Tibetan plateau and Tien Shan is predominantly continuous, and large deformation gradients only exist perpendicular to the Indo‐Eurasian relative plate motion and are associated with a few large strike‐slip faults. (b) Lateral extrusions occur on both the east and west sides of the plateau. The westward extrusion peaks at ~6 mm/yr in the Pamir‐Hindu Kush region. A bell‐shaped eastward extrusion involves most of the plateau at a maximum rate of ~20 mm/yr between the Jiali and Ganzi‐Yushu faults, and the pattern is consistent with gravitational flow in southern and southeastern Tibet where the crust shows widespread dilatation at 10–20 nanostrain/yr. (c) The southeast borderland of Tibet rotates clockwise around the eastern Himalaya syntaxis, with sinistral and dextral shear motions along faults at the outer and inner flanks of the rotation terrane. The result suggests gravitational flow accomplished through rotation and translation of smaller subblocks in the upper crust. (d) Outside of the Tibetan plateau and Tien Shan, deformation field is block‐like. However, unnegligible internal deformation on the order of a couple of nanostrain/yr is found for all blocks. The North China block, under a unique tectonic loading environment, deforms and rotates at rates significantly higher than its northern and southern neighboring blocks, attesting its higher seismicity rate and earthquake hazard potential than its neighbors.

Using the measurements of ∼726 GPS stations around the Tibetan Plateau, we determine the rigid rotation of the entire plateau in a Eurasia‐fixed reference frame which can be best described by an Euler vector of (24.38° ± 0.42°N, 102.37° ± 0.42°E, 0.7096° ± 0.0206°/Ma). The rigid rotational component accommodates at least 50% of the northeastward thrust from India and dominates the eastward extrusion of the northern plateau. After removing the rigid rotation to highlight the interior deformation within the plateau, we find that the most remarkable interior deformation of the plateau is a “glacier‐like flow” zone which starts at somewhere between the middle and western plateau, goes clockwise around the Eastern Himalayan Syntaxis (EHS), and ends at the southeast corner of the plateau with a fan‐like front. The deformation feature of the southern plateau, especially the emergence of the flow zone could be attributed to an eastward escape of highly plastic upper crustal material driven by a lower crust viscous channel flow generated by lateral compression and gravitational buoyancy at the later developmental stage of the plateau. The first‐order feature of crustal deformation of the northeastern plateau can be well explained by a three‐dimensional elastic half‐space dislocation model with rates of dislocation segments comparable to the ones from geological observations. In the eastern plateau, although GPS data show no significant convergence between the eastern margin of the plateau and the Sichuan Basin, a small but significant compressional strain rate component of ∼10.5 ± 2.8 nstrain/yr exists in a relatively narrow region around the eastern margin. In addition, a large part of the eastern plateau, northeast of the EHS, is not undergoing shortening along the northeastward convergence direction of the EHS but is stretching.

Abstract In December 2019, the International Association of Geomagnetism and Aeronomy (IAGA) Division V Working Group (V-MOD) adopted the thirteenth generation of the International Geomagnetic Reference Field (IGRF). This IGRF updates the previous generation with a definitive main field model for epoch 2015.0, a main field model for epoch 2020.0, and a predictive linear secular variation for 2020.0 to 2025.0. This letter provides the equations defining the IGRF, the spherical harmonic coefficients for this thirteenth generation model, maps of magnetic declination, inclination and total field intensity for the epoch 2020.0, and maps of their predicted rate of change for the 2020.0 to 2025.0 time period.

Abstract Large earthquakes initiate chains of surface processes that last much longer than the brief moments of strong shaking. Most moderate‐ and large‐magnitude earthquakes trigger landslides, ranging from small failures in the soil cover to massive, devastating rock avalanches. Some landslides dam rivers and impound lakes, which can collapse days to centuries later, and flood mountain valleys for hundreds of kilometers downstream. Landslide deposits on slopes can remobilize during heavy rainfall and evolve into debris flows. Cracks and fractures can form and widen on mountain crests and flanks, promoting increased frequency of landslides that lasts for decades. More gradual impacts involve the flushing of excess debris downstream by rivers, which can generate bank erosion and floodplain accretion as well as channel avulsions that affect flooding frequency, settlements, ecosystems, and infrastructure. Ultimately, earthquake sequences and their geomorphic consequences alter mountain landscapes over both human and geologic time scales. Two recent events have attracted intense research into earthquake‐induced landslides and their consequences: the magnitude M 7.6 Chi‐Chi, Taiwan earthquake of 1999, and the M 7.9 Wenchuan, China earthquake of 2008. Using data and insights from these and several other earthquakes, we analyze how such events initiate processes that change mountain landscapes, highlight research gaps, and suggest pathways toward a more complete understanding of the seismic effects on the Earth's surface.

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We derive a detailed horizontal velocity field for the southeast borderland of the Tibetan Plateau using GPS data collected from the Crustal Motion Observation Network of China between 1998 and 2004. Our results reveal a complex deformation field that indicates that the crust is fragmented into tectonic blocks of various sizes, separated by strike‐slip and transtensional faults. Most notably, the regional deformation includes 10–11 mm/yr left slip across the Xianshuihe fault, ∼7 mm/yr left slip across the Anninghe‐Zemuhe‐Xiaojiang fault zone, ∼2 mm/yr right slip across a shear zone trending northwest near the southern segment of the Lancang River fault, and ∼3 mm/yr left slip across the Lijiang fault. Deformation along the southern segment of the Red River fault appears not significant at present time. The region south and west of the Xianshuihe‐Xiaojiang fault system, whose eastward motion is resisted by the stable south China block to the east, turns from eastward to southward motion with respect to south China, resulting in clockwise rotation of its internal subblocks. Active deformation is detected across two previously unknown deformation zones: one is located ∼150 km northwest of and in parallel with the Longmenshan fault with 4–6 mm/yr right‐slip and another is continued south‐southwestward from the Xiaojiang fault abutting the Red River fault with ∼7 mm/yr left slip. While both of these zones are seismically active, the exact locations of faults responsible for such deformation are yet to be mapped by field geology. Comparing our GPS results with predictions of various models proposed for Tibetan Plateau deformation, we find that the relatively small sizes of the inferred microblocks and their rotation pattern lend support to a model with a mechanically weak lower crust experiencing distributed deformation underlying a stronger, highly fragmented upper crust.

The May 12, 2008 Wenchuan earthquake of China (Mw 7.9 or Ms 8.0) triggered hundreds of thousands of landslides. Mapping such a large number of landslides is a major task, considering the large size of the affected area and the availability of pre- and post-earthquake remote sensing images. This paper compares three (nearly) complete landslide inventories that were compiled from visual image interpretation. The three inventories differ in the manner in which the landslides are represented, either as polygons, centroid points, or top points. Landslides in the three inventories use one-to-one correspondence. Each of the three inventories includes a large proportion of the 197,481 landslides triggered by the earthquake. These landslides were delineated as individual solid polygons and points using visual interpretation of high-resolution aerial photographs and satellite images acquired following the earthquake and verified by selected field checking throughout a broad area of approximately 110,000 km2. These landslides cover a total area of approximately 1,160 km2. Based on the inventories of landslide polygons and landslide centroid points, two types of density maps were constructed. Correlations of landslide occurrence with seismic, geologic, and topographic parameters were analyzed using the three landslide inventories. Statistical analysis of their spatial distribution was performed using both the landslide area percentage (LAP), defined as the percentage of the area affected by the landslides and the landslide number density (LND), defined as the number of landslides per square kilometer. There are two types of LNDs: the LND-centroid (based on the centroid point of the landslide) and the LND-top (based on the top point of the landslide). We used the three indexes to determine how the occurrence of the landslides correlates with elevation, slope angle, slope aspect, slope position, slope curvature, lithology, distance from the epicenter, seismic intensity, distance from the Yingxiu-Beichuan surface fault rupture, peak ground acceleration (PGA), and coseismic surface displacements (including horizontal, vertical, and total displacements). Both the LAP and the two types of LND values were observed to have continuous positive or negative correlations with the slope angle, slope curvature, distance from the epicenter and from the Yingxiu-Beichuan surface fault rupture, seismic intensity, and coseismic surface displacement. In addition, the highest values of the LAP and LND values appear at ranges from 1,200 to 3,000 m in elevation. Moreover, the landslides have preferred orientations, dominated by the eastern, southeastern, and southern directions. In addition, the sandstone, siltstone (Z), and granitic rocks experienced more concentrated landslides. No obvious correlations were observed between the LAP and LND values and slope position. Finally, we studied the orders of eight earthquake-triggered landslide impact factor effect on landslide occurrence. The 197,481 landslides triggered by the 2008 Wenchuan earthquake were delineated. Three landslide inventories were constructed: polygon, centroid, and top point inventories. The landslides were spatially analyzed with topographic, lithology, and seismic parameters.

Abstract The seismological observation system in China achieved rapid development during the last five years. The Data Management Center (DMC) of the China Earthquake Network Center (CENC) of the China Earthquake Administration (CEA) now receives and archives waveform data from more than 1000 permanent seismic stations around China in real time. For operational, backup, and data security considerations, the DMC at the Institute of Geophysics (IGP), the CEA was established at the end of 2007. The IGPDMC is capable of receiving and processing continuous waveform data in real time from more than 1000 permanent seismic stations around China. Currently, the data processing and management mainly include data quality control, data format conversion, event data extraction at user’s request, and data download service via Internet. By now, the IGPDMC has supplied about 150 terabytes waveform data to over 120 researches of more than 30 academic institutions. More than 20 papers have been published in professional journals. After the great Wenchuan earthquake, the real-time waveform data from 56 portable stations deployed in the aftershock area were added to IGPDMC. All these data make the IGPDMC a critical platform for supporting relevant seismological research. This paper gives a detailed description of the permanent seismic stations of the CEA’s seismological observation system, the technical system construction of the IGPDMC, establishment of the near-real-time automatic event-extraction system for large earthquakes, as well as the prompt data support to Wenchuan earthquake-related researches.

Abstract Recent studies of the northeastern part of the Tibetan Plateau have called attention to two emerging views of how the Tibetan Plateau has grown. First, deformation in northern Tibet began essentially at the time of collision with India, not 10–20 Myr later as might be expected if the locus of activity migrated northward as India penetrated the rest of Eurasia. Thus, the north‐south dimensions of the Tibetan Plateau were set mainly by differences in lithospheric strength, with strong lithosphere beneath India and the Tarim and Qaidam basins steadily encroaching on one another as the region between them, the present‐day Tibetan Plateau, deformed, and its north‐south dimension became narrower. Second, abundant evidence calls for acceleration of deformation, including the formation of new faults, in northeastern Tibet since ~15 Ma and a less precisely dated change in orientation of crustal shortening since ~20 Ma. This reorientation of crustal shortening and roughly concurrent outward growth of high terrain, which swings from NNE‐SSW in northern Tibet to more NE‐SW and even ENE‐WSW in the easternmost part of northeastern Tibet, are likely to be, in part, a consequence of crustal thickening within the high Tibetan Plateau reaching a limit, and the locus of continued shortening then migrating to the northeastern and eastern flanks. These changes in rates and orientation also could result from removal of some or all mantle lithosphere and increased gravitational potential energy per unit area and from a weakening of crustal material so that it could flow in response to pressure gradients set by evolving differences in elevation.

Abstract The India‐Eurasia collision zone is the largest deforming region on the planet; direct measurements of present‐day deformation from Global Positioning System (GPS) have the potential to discriminate between competing models of continental tectonics. But the increasing spatial resolution and accuracy of observations have only led to increasingly complex realizations of competing models. Here we present the most complete, accurate, and up‐to‐date velocity field for India‐Eurasia available, comprising 2576 velocities measured during 1991–2015. The core of our velocity field is from the Crustal Movement Observation Network of China‐I/II: 27 continuous stations observed since 1999; 56 campaign stations observed annually during 1998–2007; 1000 campaign stations observed in 1999, 2001, 2004, and 2007; 260 continuous stations operating since late 2010; and 2000 campaign stations observed in 2009, 2011, 2013, and 2015. We process these data and combine the solutions in a consistent reference frame with stations from the Global Strain Rate Model compilation, then invert for continuous velocity and strain rate fields. We update geodetic slip rates for the major faults (some vary along strike), and find that those along the major Tibetan strike‐slip faults are in good agreement with recent geological estimates. The velocity field shows several large undeforming areas, strain focused around some major faults, areas of diffuse strain, and dilation of the high plateau. We suggest that a new generation of dynamic models incorporating strength variations and strain‐weakening mechanisms is required to explain the key observations. Seismic hazard in much of the region is elevated, not just near the major faults.

Measurements at 400 campaign-style GPS points and another 14 continuously recording stations in central Asia define variations in their velocities both along and across the Kyrgyz and neighboring parts of Tien Shan. They show that at the longitude of Kyrgyzstan the Tarim Basin converges with Eurasia at 20 2 mm/yr, nearly two thirds of the total convergence rate between India and Eurasia at this longitude. This high rate suggests that the Tien Shan has grown into a major mountain range only late in the evolution of the India-Eurasia collision. Most of the convergence between Tarim and Eurasia within the upper crust of the Tien Shan presumably occurs by slip on faults on the edges of and within the belt, but 1-3 mm/yr of convergence is absorbed farther north, at the Dzungarian Alatau and at a lower rate with the Kazakh platform to the west. The Tarim Basin is thrust beneath the Tien Shan at 4-7 mm/yr. With respect to Eurasia, the Ferghana Valley rotates counterclockwise at 0.7Myr -1 about an axis at the southwest end of the valley. Thus, GPS data place a bound of 4 mm/yr on the rate of crustal shortening across the Chatkal and neighboring ranges on the northwest margin of the Ferghana Valley, and they limit the present-day slip rate on the right-lateral Talas-Ferghana fault to less than 2 mm/yr. GPS measurements corroborate geologic evidence indicating that the northern margin of the Pamir overthrusts the Alay Valley and require a rate of at least 10 and possibly 15 mm/yr.

Abstract Using the measurements of 750 GPS stations around the Tibetan Plateau for over 10 years since 1999, we derived a high‐resolution 3‐D velocity field for the present‐day crustal movement of the plateau. The horizontal velocity field relative to stable Eurasia displays in details the crustal movement and tectonic deformation features of the India‐Eurasia continental collision zone with thrust compression, lateral extrusion, and clockwise rotation. The vertical velocity field reveals that the Tibetan Plateau is continuing to rise as a whole relative to its stable north neighbor. However, in some subregions, uplift is insignificant or even negative. The main features of the vertical crustal deformation of the plateau are the following: (a) The Himalayan range is still rising at a rate of ~2 mm/yr. The uplift rate is ~6 mm/yr with respect to the south foot of the Himalayan range. (b) The middle eastern plateau has a typical uplift rate between 1 and 2 mm/yr, and some high mountain ranges in this area, like the Longmen Shan and Gongga Shan, have surprising uplift rates as large as 2–3mm/yr. (c) In the middle southern plateau, there is a basin and endorheic subregion with a series of NS striking normal faults, showing obvious sinking with the rates between 0 and ‐3 mm/yr. (d) The present‐day rising and sinking subregions generally correspond well to the Cenozoic orogenic belts and basins, respectively. (e) At the southeastern corner of the plateau. There is an apparent trend that the uplift rate is gradually decreasing from between 0.8 and 2.3 mm/yr in the inner plateau to between ‐0.5 and ‐1.6 mm/yr outside the plateau, with the decrease of terrain height.

Following the 2009 L'Aquila earthquake, the Dipartimento della Protezione Civile Italiana (DPC), appointed an International Commission on Earthquake Forecasting for Civil Protection (ICEF) to report on the current state of knowledge of short-term prediction and forecasting of tectonic earthquakes and indicate guidelines for utilization of possible forerunners of large earthquakes to drive civil protection actions, including the use of probabilistic seismic hazard analysis in the wake of a large earthquake. The ICEF reviewed research on earthquake prediction and forecasting, drawing from developments in seismically active regions worldwide. A prediction is defined as a deterministic statement that a future earthquake will or will not occur in a particular geographic region, time window, and magnitude range, whereas a forecast gives a probability (greater than zero but less than one) that such an event will occur. Earthquake predictability, the degree to which the future occurrence of earthquakes can be determined from the observable behavior of earthquake systems, is poorly understood. This lack of understanding is reflected in the inability to reliably predict large earthquakes in seismically active regions on short time scales. Most proposed prediction methods rely on the concept of a diagnostic precursor; i.e., some kind of signal observable before earthquakes that indicates with high probability the location, time, and magnitude of an impending event. Precursor methods reviewed here include changes in strain rates, seismic wave speeds, and electrical conductivity; variations of radon concentrations in groundwater, soil, and air; fluctuations in groundwater levels; electromagnetic variations near and above Earth's surface; thermal anomalies; anomalous animal behavior; and seismicity patterns. The search for diagnostic precursors has not yet produced a successful short-term prediction scheme. Therefore, this report focuses on operational earthquake forecasting as the principle means for gathering and disseminating authoritative information about time-dependent seismic hazards to help communities prepare for potentially destructive earthquakes. On short time scales of days and weeks, earthquake sequences show clustering in space and time, as indicated by the aftershocks triggered by large events. Statistical descriptions of clustering explain many features observed in seismicity catalogs, and they can be used to construct forecasts that indicate how earthquake probabilities change over the short term. Properly applied, short-term forecasts have operational utility; for example, in anticipating aftershocks that follow large earthquakes. Although the value of long-term forecasts for ensuring seismic safety is clear, the interpretation of short-term forecasts is problematic, because earthquake probabilities may vary over orders of magnitude but typically remain low in an absolute sense (< 1% per day). Translating such low-probability forecasts into effective decision-making is a difficult challenge. Reports on the current utilization operational forecasting in earthquake risk management were compiled for six countries with high seismic risk: China, Greece, Italy, Japan, Russia, United States. Long-term models are currently the most important forecasting tools for civil protection against earthquake damage, because they guide earthquake safety provisions of building codes, performance-based seismic design, and other risk-reducing engineering practices, such as retrofitting to correct design flaws in older buildings. Short-term forecasting of aftershocks is practiced by several countries among those surveyed, but operational earthquake forecasting has not been fully implemented (i.e., regularly updated and on a national scale) in any of them. Based on the experience accumulated in seismically active regions, the ICEF has provided to DPC a set of recommendations on the utilization of operational forecasting in Italy, which may also be useful in other countries. The public should be provided with open sources of information about the short-term probabilities of future earthquakes that are authoritative, scientific, consistent, and timely. Advisories should be based on operationally qualified, regularly updated seismicity forecasting systems that have been rigorously reviewed and updated by experts in the creation, delivery, and utility of earthquake information. The quality of all operational models should be evaluated for reliability and skill by retrospective testing, and they should be under continuous prospective testing against established long-term forecasts and alternative time-dependent models. Alert procedures should be standardized to facilitate decisions at different levels of government and among the public. Earthquake probability thresholds should be established to guide alert levels based on objective analysis of costs and benefits, as well as the less tangible aspects of value-of-information, such as gains in psychological preparedness and resilience. The principles of effective public communication established by social science research should be applied to the delivery of seismic hazard information.

Abstract We reconstructed Philippine Sea and East Asian plate tectonics since 52 Ma from 28 slabs mapped in 3‐D from global tomography, with a subducted area of ~25% of present‐day global oceanic lithosphere. Slab constraints include subducted parts of existing Pacific, Indian, and Philippine Sea oceans, plus wholly subducted proto‐South China Sea and newly discovered “East Asian Sea.” Mapped slabs were unfolded and restored to the Earth surface using three methodologies and input to globally consistent plate reconstructions. Important constraints include the following: (1) the Ryukyu slab is ~1000 km N‐S, too short to account for ~20° Philippine Sea northward motion from paleolatitudes; (2) the Marianas‐Pacific subduction zone was at its present location (±200 km) since 48 ± 10 Ma based on a >1000 km deep slab wall; (3) the 8000 × 2500 km East Asian Sea existed between the Pacific and Indian Oceans at 52 Ma based on lower mantle flat slabs; (4) the Caroline back‐arc basin moved with the Pacific, based on the overlapping, coeval Caroline hot spot track. These new constraints allow two classes of Philippine Sea plate models, which we compared to paleomagnetic and geologic data. Our preferred model involves Philippine Sea nucleation above the Manus plume (0°/150°E) near the Pacific‐East Asian Sea plate boundary. Large Philippine Sea westward motion and post‐40 Ma maximum 80° clockwise rotation accompanied late Eocene‐Oligocene collision with the Caroline/Pacific plate. The Philippine Sea moved northward post‐25 Ma over the northern East Asian Sea, forming a northern Philippine Sea arc that collided with the SW Japan‐Ryukyu margin in the Miocene (~20–14 Ma).

Abstract Although deep carbon recycling plays an important role in the atmospheric CO2 budget and climate changes through geological time, the precise mechanisms remain poorly understood. Since recycled sedimentary carbonate through plate subduction is the main light-δ26Mg reservoir within deep-Earth, Mg isotope variation in mantle-derived melts provides a novel perspective when investigating deep carbon cycling. Here, we show that the Late Cretaceous and Cenozoic continental basalts from 13 regions covering the whole of eastern China have low δ26Mg isotopic compositions, while the Early Cretaceous basalts from the same area and the island arc basalts from circum-Pacific subduction zones have mantle-like or heavy Mg isotopic characteristics. Thus, a large-scale mantle low δ26Mg anomaly in eastern China has been delineated, suggesting the contribution of sedimentary carbonates recycled into the upper mantle, but limited into the lower mantle. This large-scale spatial and temporal variation of Mg isotopes in the mantle places severe constraints on deep carbon recycling via oceanic subduction.

Using data from more than 2000 seismic stations from multiple networks arrayed throughout China (CEArray, China Array, NECESS, PASSCAL, GSN) and surrounding regions (Korean Seismic Network, F-Net, KNET), we perform ambient noise Rayleigh wave tomography across the entire region and earthquake tomography across parts of South China and Northeast China. We produce isotropic Rayleigh wave group and phase speed maps with uncertainty estimates from 8 to 50 s period across the entire region of study, and extend them to 70 s period where earthquake tomography is performed. Maps of azimuthal anisotropy are estimated simultaneously to minimize anisotropic bias in the isotropic maps, but are not discussed here. The 3D model is produced using a Bayesian Monte Carlo formalism covering all of China, extending eastwards through the Korean Peninsula, into the marginal seas, to Japan. We define the final model as the mean and standard deviation of the posterior distribution at each location on a 0.5° × 0.5° grid from the surface to 150 km depth. Surface wave dispersion data do not strongly constrain internal interfaces, but shear wave speeds between the discontinuities in the crystalline crust and uppermost mantle are well determined. We design the resulting model as a reference model, which is intended to be useful to other researchers as a starting model, to predict seismic wave fields and observables and to predict other types of data (e.g. topography, gravity). The model and the data on which it is based are available for download. In addition, the model displays a great variety and considerable richness of geological and tectonic features in the crust and in the uppermost mantle deserving of further focus and continued interpretation.

New apatite (U-Th)/He from the northeastern
\nmargin of the Tibetan Plateau (north
\nQilian Shan) indicate rapid cooling began at
\n~10 Ma, which is attributed to the onset of
\nfaulting and topographic growth. Preservation
\nof the paleo-PRZ in the hanging wall and
\ngrowth strata in the footwall allow us to calculate
\nvertical and horizontal fault slip rates
\naveraged over the last 10 Myr of ~0.5 mm/yr
\nand ~1 mm/yr respectively, which are within
\na factor of two consistent with Holocene slip
\nrates and geodetic data. Low fault slip rates
\nsince the initiation of the northern Qilian
\nShan fault suggest that total horizontal offset
\ndid not exceed 10 km. Further, emergence
\nof the northern Qilian Shan occurs during
\na period of increased aridity in northern
\nTibet but is associated with only a minor
\nexpansion of the northern plateau perimeter,
\nwhich is well established near collision
\ntime. Outgrowth of the northern Qilian Shan
\nat ~10 Ma could be simple propagation of
\nthe larger Qilian Shan system, occurring in
\nresponse to decreased slip rates on the Altyn
\nTagh fault or as a result of the change in GPE
\nof the central plateau.

Abstract An orthogonal set of principal axes is defined for earthquake ground motions along which the component variances have maximum, minimum and intermediate values and the covariances equal zero. Corresponding axes are defined which yield maximum values for the covariances. The orthogonal transformations involved are identical in form to those used in the transformation of stress. Examination of real accelerograms reveals that the major principal axis points in the general direction of the epicentre and the minor principal axis is nearly vertical. It is concluded that artificially generated components of ground motion need not be correlated statistically provided they are directed along a set of principal axes.