Wave Arrival Times Research Articles

Big mantle wedge, anisotropy, slabs and earthquakes beneath the Japan Sea

The Japan Sea is a part of the western Pacific trench-arc-backarc system and has a complex bathymetry and intense seismic activities in the crust and upper mantle. Local seismic tomography revealed strong lateral heterogeneities in the crust and uppermost mantle beneath the eastern margin of the Japan Sea, which was determined using P and S wave arrival times of suboceanic earthquakes relocated precisely with sP depth phases. Ambient-noise tomography revealed a thin crust and a thin lithosphere beneath the Japan Sea and significant low-velocity (low-V) anomalies in the shallow mantle beneath the western and eastern margins of the Japan Sea. Observations with ocean-bottom seismometers and electromagnetometers revealed low-V and high-conductivity anomalies at depths of 200–300km in the big mantle wedge (BMW) above the subducting Pacific slab, and the anomalies are connected with the low-V zone in the normal mantle wedge beneath NE Japan, suggesting that both shallow and deep slab dehydrations occur and contribute to the arc and back-arc magmatism. The Pacific slab has a simple geometry beneath the Japan Sea, and earthquakes occur actively in the slab down to a depth of ∼600km beneath the NE Asian margin. Teleseismic P and S wave tomography has revealed that the Philippine Sea plate has subducted aseismically down to the mantle transition zone (MTZ, 410–660km) depths beneath the southern Japan Sea and the Tsushima Strait, and a slab window is revealed within the aseismic Philippine Sea slab. Seismic anisotropy tomography revealed a NW-SE fast-velocity direction in the BMW, which reflects corner flows induced by the fast deep subduction of the Pacific slab. Large deep earthquakes (M>7.0; depth>500km) occur frequently beneath the Japan Sea western margin, which may be related to the formation of the Changbai and Ulleung intraplate volcanoes. A metastable olivine wedge is revealed within the cold core of the Pacific slab at the MTZ depth, which may be related to the deep seismicity. However, many of these results are still preliminary, due to the lack of seismic stations in the Japan Sea. The key to resolving these critical geoscientific issues is seismic instrumentation in the Japan Sea, for which international cooperation of geoscience communities in the East Asian countries is necessary.

Laser Ultrasound Observations of Mechanical Property Variations in Ice Cores

The study of climate records in ice cores requires an accurate determination of annual layering within the cores in order to establish a depth-age relationship. Existing tools to delineate these annual layers are based on observations of changes in optical, chemical, and electromagnetic properties. In practice, no single technique captures every layer in all circumstances. Therefore, the best estimates of annual layering are produced by analyzing a combination of measurable ice properties. We present a novel and complimentary elastic wave remote sensing method based on laser ultrasonics. This method is used to measure variations in ultrasonic wave arrival times and velocity along the core with millimeter resolution. The laser ultrasound system does not require contact with the ice core and is non-destructive. Custom optical windows allow the source and receiver lasers to be located outside the cold room, while the core is scanned by moving it with a computer-controlled stage. We present results from Antarctic firn and ice cores that lack visual evidence of a layered structure, but do show travel-time and velocity variations. In the future, these new data may be used to infer stratigraphic layers from elastic parameter variations within an ice core, as well as analyze ice crystal fabrics.

Shear building stiffness estimation by wave traveling time analysis

A novel damage identification technique to estimate stiffness in a multistory building supported on solid ground is presented. Based on a shear building model, a 1-dimensional wave equation for a vertically propagating shear wave is derived. A Ricker pulse is used as excitation signal and propagated through the building. Wave propagation in the building is based on the Thomson–Haskell method, where each story is represented as a single layer in a multiple stratum model. The wave arrival times of the pulse at each story are used to calculate the stiffness of the columns. The involved calculations in this method grow only linearly with the number of stories, as opposed to other identification methods, as modal analysis, that grow geometrically; this makes this approach an interesting alternative method to asses building integrity. Simulation result for a building with heterogeneous characteristics across the stories confirms the feasibility of the proposal.

Latitudinal beaming of Jovian decametric radio emissions as viewed from Juno and the Nançay Decameter Array

AbstractTwo well‐defined Jovian decametric radio arcs were observed at latitudinal separations of 11°–16° from the Juno spacecraft near Jupiter and the Nançay Decameter Array (NDA) at Earth on 17 May and 25 August 2016. These discrete arcs are from the so‐called A source covering both Io‐related and non‐Io‐related emissions. By measuring the wave arrival time at two distant observers with propagation time correction, the remaining delay times are 92.8 ± 1.3 min for the first arc and 116.0 ± 1.2 min for the second arc. This implies that both radio sources are not controlled by the orbital motion of Io but Jupiter's rotation itself. The geometrical information for Juno and NDA and the loss cone‐driven electron cyclotron maser instability theory provide these radio sources that are located at about 173° ± 10° in system III longitude projected onto Jupiter's north surface and imply resonant electron energy ranges from 0.5 to 11 keV.

A critical assessment of the in-vitro measurement of cortical bone stiffness with ultrasound

Elasticity assessment based on bulk wave velocity (BWV) measurements is the most popular technique to characterize the anisotropic stiffness tensor in cortical bone. Typically, a cuboid bone specimen is cut with its sides along the different anatomical directions. Then, the velocity of shear and longitudinal waves propagating along different directions are assessed, from which stiffness coefficients are calculated. Despite the importance of obtaining accurate elasticity values for bone research, there is no generally accepted protocol to measure BWV and the precision of the technique has been seldom investigated. The purpose of this work is to critically assess the method to measure BWV on cuboid specimens in terms of ultrasound frequency, specimen size and signal processing technique. In this study, we measured polycarbonate specimens of different dimensions and 55 human bone specimens with different transducers using frequencies ranging from 2.25 to 10MHz and 1–5MHz for longitudinal and shear waves, respectively. We compared four signal processing methods to detect the wave arrival time. The main results are that, (1) the measurement of shear waves is more complex than that of longitudinal wave, being less precise and more sensitive to sample size; (2) the estimated stiffness depends on the signal processing technique used (up to 10% variation for shear coefficients of bone); and (3) bone stiffness assessed from BWV using the first arrival of the signal to determine the time-of-flight is not different from stiffness assessed using resonant ultrasound spectroscopy (RUS). These results evidence that the measurement method can have an effect on the stiffness values estimates and hence, a well-defined protocol is needed to accurately measure bone stiffness coefficients based on BWV.

Seismic imaging of the crust and uppermost mantle beneath the Qilian Orogenic Belt and its geodynamic implications

Three-dimensional (3-D) seismic velocity structure of the crust and uppermost mantle under the Qilian Orogenic Belt (QLOB) is important for better understanding the Cenozoic deformation mechanism of the QLOB and the deep tectonic relationship between the QLOB and the Alashan Block. We determined a detailed 3-D P and S wave velocity (Vp and Vs) model of the crust and uppermost mantle beneath the QLOB and its adjacent regions. The data set used in this study consists of 75,999 P wave and 72,178 S wave arrival times of 7485 local earthquakes recorded by 72 seismic stations in the study area during 2009 to 2015. Our tomographic results show obvious low-velocity (low-V) anomalies in the lower crust beneath the QLOB, and the low-V zones extend to the uppermost mantle beneath a few local areas. These features are interpreted as mechanically weakened zones caused by fluids and melt related to the northward extension of the Tibetan Plateau and local hot upwelling in the upper mantle. The weakened zones in the lower crust are capable of ductile flow on a geological timescale, and the intermittent distribution of the low-V zones indicates that the scale of the ductile flow is not very large. The obtained Vp and Vs images indicate southward subduction of the Alashan Block beneath the QLOB, which may result from the Indo-Eurasia collision. Large crustal earthquakes in the study region generally occurred along large fault zones where Vp and Vs change drastically over a short distance. Beneath source areas of the large earthquakes, low-V anomalies caused by fluids and melt exist widely in the lower crust and uppermost mantle. When the fluids migrate upward to the active faults in the upper crust, the fault zone friction is reduced and so large crustal earthquakes can be triggered.

The Effect of Ambient Pressure on Blast Reflected Impulse and Overpressure

Reflected blast pressure and impulse for bare 226.8 g spherical C-4 charges under various atmospheric pressure conditions were studied both experimentally and numerically. Blast pressure measurements were conducted using an array of high resonant frequency tourmaline-based piezoelectric pressure transducers to record normally reflected blast pressure histories at a 61 cm standoff. The explosive detonation and pressure measurements were conducted inside a pressure vessel which allowed the ambient pressure surrounding the C-4 charge to be varied. The recorded pressure histories were analyzed for blast wave arrival time, peak reflected overpressure, and positive phase impulse. The numerical analysis of blast pressures under varying ambient conditions was conducted using an axi-symmetric Arbitrary Lagrangian Eulerian (ALE) finite element technique with LS-DYNA. Numerical predictions were carried out for a 61 cm standoff that allowed direct comparison to the measured data. Additionally, the ALE simulations considered the effects of ambient pressure on blast impulse for varying standoff distances in the range of 12.7 to 61 cm. At a 61 cm standoff, measured peak reflected pressures showed no significant effect of varying ambient pressure while normally reflected impulses increased with increasing ambient pressure. Predictions by LS-DYNA for standoffs less than 61 cm showed a decreasing effect of ambient pressure on the normally reflected impulse as the standoff distance decreased. For small standoff distances it was predicted that the effects of ambient air pressure on normally reflected impulse were not significant. As the standoff distance between the explosive charge and the reflecting structure increases, higher ambient air pressures did cause a significant increase in reflected impulse.

Traveling-Wave-Based Fault-Location Algorithm for Hybrid Multiterminal Circuits

This paper presents a traveling-wave-based fault-location algorithm for hybrid multiterminal transmission systems that consist of one onshore overhead lines and multiple offshore submarine cables. Such hybrid transmission systems are common for interconnection of offshore wind farms to the main grid. The input to the algorithm is synchronized transient voltage measurements from all of the receiving ends. These measurements are obtained by optical voltage transducers equipped with global positioning system receivers for time synchronization. The discrete wavelet transformation is utilized to decompose the mode-1 voltages at the receiving ends. The first wave arrival times are then obtained by observing the squares of the wavelet transformation coefficient (WTC 2 ). The transient simulations and the postfault analysis are carried out using EMTP-RV and MATLAB Wavelet Toolbox, respectively. The accuracy, limitations, and capabilities of the proposed algorithm are presented and discussed for different fault conditions.

SPECIFIC VELOCITY STRUCTURE OF THE UPPER MANTLE IN THE TRANSBAIKALIA SEGMENT OF THE MONGOLIA-OKHOTSK OROGENIC BELT

The paper presents the results of deep seismic studies on Geophysical Reference Profile 1-SB (Sredneargunsk – Ust-Karenga – Taksimo – Vitim) in East Transbaikalia,Russia. The1200 kmlong profile crosses the major tectonic structures of the Central Asian fold belt: the Argun median massif, the Selenga-Stanovoy and Transbaikalia folded regions, and the Baikal rift zone. Its northwestern fragment extends into the Angara-Lena monocline of the Siberian platform. The southeastern (Transbaikalia) and northwestern (Baikal-Patom) fragments of the profile are based on the spot (differential) seismic sounding technique using explosions and 40-tonne vibrators. The south­eastern (Transbaikalia) fragment shows small crustal thickness values (~40 km), an almost horizontal position of the Moho, and high velocities of longitudinal waves (~8.4 km/sec) beneath the Moho. The analysis of parallelism graphs and the dynamic expression of the wave refracted from the Moho suggests a less than 5–10 km thick layer of high velocities and low gradients below Moho. The database on theterritoryofTransbaikaliaincludes ~200 wave arrival times from large earthquakes, which were refracted at the Moho at distances of ~200–1400 km. As part of the tomographic interpretation, using additional DSS data on the Moho, theterritoryofTransbaikaliahas been mapped to show the patterns of the threshold velocity values at the Moho. The seismic data was used to contour an area with high velocity values in the mantle in the central part of the Mongolia-Okhotsk orogenic belt and the neighboring fold structures of Transbaikalia. According to the analysis of the seismic and geologic data on the study area, the mantle layer with high velocity values in the Mongolian-Okhotsk orogenic belt may be represented by the eclogitic rock plates.

Traveling-Wave Detection Technique using Short-Time Matrix Pencil Method

This paper proposes a new technique for detection of traveling-wave arrival times in power systems. Precise estimation of wave arrival times improves most of the traveling-wave-based fault location methods. The proposed technique is based on the short-time matrix pencil method that decomposes the measurement samples in a sliding window into time-indexed complex frequencies. Traveling-wave arrival times are estimated based on the fact that the extracted damping factors (i.e., the real part of the complex frequencies) are zero when the arriving wave is located in the middle of the sliding window. The proposed technique is compared to the existing transient-detection techniques such as discrete wavelet transform with commonly used mother wavelets and Hilbert transform (HT), using MATLAB Wavelet Toolbox and MATLAB HT. The sensitivity analysis based on the simulation results demonstrates that the proposed technique is less affected by the measurement noise, sampling frequency, and fault parameters.

Tsunami simulation due to seaquake at Manila Trench and Sulu Trench

Seaquake is a phenomenon where there are water disturbance at the sea, caused by earthquake or submarine eruption. The scope of this study focuses on tsunami simulation due to Manila Trench and Sulu Trench seaquake which is prone to harm Malaysia offshore areas. Manila Trench is a highly potential earthquake source that can generate tsunami in South China Sea. Meanwhile, Sulu Trench could be a threat to east of Sabah offshore areas. In this study, TUNA-M2 model was utilized to perform tsunami simulation at South China Sea and Sulu Sea. TUNA-M2 model applied Okada source model to create tsunami generation due to earthquake. It utilized linear shallow water equation during tsunami propagation with its radiant boundary condition. Five simulations performed at each study region. Forecast points at South China Sea areas were divided into three separate locations which are at the Peninsular Malaysia, west of Sabah and Sarawak offshore areas. Forecast points at Sulu Sea were focused at the east of Sabah offshore areas. This paper will present the simulation results of tsunami wave height and arrival time at various forecast points. The findings of this study show that the range of tsunami wave height at Sulu Sea is higher than that of South China Sea. The tsunami arrival time at Sulu Sea is less than South China Sea. It can be concluded that Sulu Sea poses worse tsunami threat than South China Sea to the Malaysian offshore areas.

Influence of road network and population demand assumptions in evacuation modeling for distant tsunamis

Tsunami evacuation planning in coastal communities is typically focused on local events where at-risk individuals must move on foot in a matter of minutes to safety. Less attention has been placed on distant tsunamis, where evacuations unfold over several hours, are often dominated by vehicle use and are managed by public safety officials. Traditional traffic simulation models focus on estimating clearance times but often overlook the influence of varying population demand, alternative modes, background traffic, shadow evacuation, and traffic management alternatives. These factors are especially important for island communities with limited egress options to safety. We use the coastal community of Balboa Island, California (USA), as a case study to explore the range of potential clearance times prior to wave arrival for a distant tsunami scenario. We use a first-in–first-out queuing simulation environment to estimate variations in clearance times, given varying assumptions of the evacuating population (demand) and the road network over which they evacuate (supply). Results suggest clearance times are less than wave arrival times for a distant tsunami, except when we assume maximum vehicle usage for residents, employees, and tourists for a weekend scenario. A two-lane bridge to the mainland was the primary traffic bottleneck, thereby minimizing the effect of departure times, shadow evacuations, background traffic, boat-based evacuations, and traffic light timing on overall community clearance time. Reducing vehicular demand generally reduced clearance time, whereas improvements to road capacity had mixed results. Finally, failure to recognize non-residential employee and tourist populations in the vehicle demand substantially underestimated clearance time.

Comparison of Robust Methods for Shear Wave Speed Estimation by Simulation

Mechanical properties of tissue are often related to the pathological state of tissue. Therefore, non-invasively measuring tissue stiffness has important clinical applications. With the assumption of isotropy, incompressibility and linearity, the shear modulus of tissue is related to its shear wave propagation speed. Acoustic radiation force from a focused ultrasound beam can be used to generate shear waves at the focal region within tissue, which propagate orthogonally to the direction of the pushing ultrasound beam. The shear wave speed can be estimated based on the so called time-to-flight principle. The shear wave arrival time determined at several lateral positions along the shear wave propagation path can be measured by the displacement profiles, which can be tracked using correlation-based method by pulse-echo ultrasound. This approach has been successively used with various modifications by several groups. The purpose of this study is to design a simulation method to generate the pulse-echo ultrasound signal, calculate the displacement profile in the spatial and time domain, and estimate the shear wave speed using RANSAC, Radon Sum and robust linear regression method, compare and analyze the algorithm performance of these methods.

Remote Sensing-Derived Water Extent and Level to Constrain Hydraulic Flood Forecasting Models: Opportunities and Challenges

Accurate, precise and timely forecasts of flood wave arrival time, depth and velocity at each point of the floodplain are essential to reduce damage and save lives. Current computational capabilities support hydraulic models of increasing complexity over extended catchments. Yet a number of sources of uncertainty (e.g., input and boundary conditions, implementation data) may hinder the delivery of accurate predictions. Field gauging data of water levels and discharge have traditionally been used for hydraulic model calibration, validation and real-time constraint. However, the discrete spatial distribution of field data impedes the testing of the model skill at the two-dimensional scale. The increasing availability of spatially distributed remote sensing (RS) observations of flood extent and water level offers the opportunity for a comprehensive analysis of the predictive capability of hydraulic models. The adequate use of the large amount of information offered by RS observations triggers a series of challenging questions on the resolution, accuracy and frequency of acquisition of RS observations; on RS data processing algorithms; and on calibration, validation and data assimilation protocols. This paper presents a review of the availability of RS observations of flood extent and levels, and their use for calibration, validation and real-time constraint of hydraulic flood forecasting models. A number of conclusions and recommendations for future research are drawn with the aim of harmonising the pace of technological developments and their applications.

Seismic velocity azimuthal anisotropy of the Japan subduction zone: Constraints from P and S wave traveltimes

AbstractWe present 3‐D images of azimuthal anisotropy tomography of the crust and upper mantle of the Japan subduction zone, which are determined using a large number of high‐quality P and S wave arrival time data of local earthquakes and teleseismic events. A tomographic method for P wave velocity azimuthal anisotropy is modified and extended to invert S wave traveltimes for 3‐D S wave velocity azimuthal anisotropy. A joint inversion of the P and S wave data is conducted to constrain the 3‐D azimuthal anisotropy of the Japan subduction zone. Our results show that the subducting Pacific and Philippine Sea (PHS) slabs exhibit mainly trench‐parallel fast‐velocity directions (FVDs), which may reflect frozen‐in lattice‐preferred orientation of aligned anisotropic minerals formed at the mid‐ocean ridge as well as shape‐preferred orientation such as normal faults produced at the outer‐rise area near the trench axis. Trench‐normal FVDs are generally revealed in the mantle wedge, which may reflect corner flows in the mantle wedge due to the plate subduction and dehydration. Trench‐normal FVDs are also visible in the subslab mantle, which may reflect the subducting asthenosphere underlying the slabs. Our results also reveal toroidal mantle flows in and around a window (hole) in the PHS slab beneath SW Japan, suggesting that the occurrence of the PHS slab window may have caused a complex flow pattern in the mantle wedge above the Pacific slab.

Study and numerical modeling of 1945 Makran tsunami due to a probable submarine landslide

The Makran subduction zone (MSZ), located along the southern coasts of Iran and Pakistan, has experienced some deadly earthquakes and tsunamis, including the destructive 1945 Makran tsunami that led to more than 4000 fatalities. In spite of past studies on 1945 Makran tsunami, there are still unresolved problems, particularly on mismatches between the tsunami wave heights and arrival times with reported observations at different locations. The significant disagreement between the results of numerical models and existing data supports the existence of another mechanism involved during the generation of the tsunami. In the present study, a submarine landslide, triggered by the 1945 Earthquake, is studied as the major source of 1945 Makran tsunami. The simulation of seismic 1945 Tsunami, using high-resolution bathymetry data with a fine nested grid to increase the accuracy of modeled tsunami wave heights, confirms the large discrepancies between the reported tsunami waves and simulated values. Assuming the location and dimensions of a probable landslide, the GEOWAVE model, a combination of TOPICS and FUNWAVE models, is applied to model the non-seismic 1945 Tsunami. The simulated landslide tsunami demonstrates a fair agreement with the reported tsunami wave heights at different locations in Pakistan, Iran and India. The arrival times of tsunami waves at Pasni and Karachi in Pakistan can also be interpreted if the occurrence time of the probable submarine landslide is assumed with 3.5 h delay after the quake. The study highlights the potential danger of a non-seismic landslide tsunami in unconsolidated sediments at the MSZ and the necessity of the development of suitable countermeasures against other potential Makran tsunamis in future.

A new algorithm for three‐dimensional joint inversion of body wave and surface wave data and its application to the Southern California plate boundary region

AbstractWe introduce a new algorithm for joint inversion of body wave and surface wave data to get better 3‐D P wave (Vp) and S wave (Vs) velocity models by taking advantage of the complementary strengths of each data set. Our joint inversion algorithm uses a one‐step inversion of surface wave traveltime measurements at different periods for 3‐D Vs and Vp models without constructing the intermediate phase or group velocity maps. This allows a more straightforward modeling of surface wave traveltime data with the body wave arrival times. We take into consideration the sensitivity of surface wave data with respect to Vp in addition to its large sensitivity to Vs, which means both models are constrained by two different data types. The method is applied to determine 3‐D crustal Vp and Vs models using body wave and Rayleigh wave data in the Southern California plate boundary region, which has previously been studied with both double‐difference tomography method using body wave arrival times and ambient noise tomography method with Rayleigh and Love wave group velocity dispersion measurements. Our approach creates self‐consistent and unique models with no prominent gaps, with Rayleigh wave data resolving shallow and large‐scale features and body wave data constraining relatively deeper structures where their ray coverage is good. The velocity model from the joint inversion is consistent with local geological structures and produces better fits to observed seismic waveforms than the current Southern California Earthquake Center (SCEC) model.

RETRACTED ARTICLE: Signal detection based on empirical mode decomposition and Teager–Kaiser energy operator and its application to P and S wave arrival time detection in seismic signal analysis

Determining P and S wave arrival times while minimizing noise is a major problem in seismic signal analysis. Precise determination of earthquake onset arrival timing, determination of earthquake magnitude, and calculation of other parameters that can be used to make more accurate seismic maps are possible with the detection of these waves. Experts try to determine these waves by manual analysis. But this process is time-consuming and painful. In this study, a new method that enables the determination of P and S wave arrival times in noisy recordings is recommended. This method is based on the hybrid usage of empirical mode decomposition and Teager---Kaiser energy operator algorithms. The results show that the proposed system gives effective results in the automatic detection of P and S wave arrival times. Promisingly, the recommended system might serve as a novel and powerful candidate for the effective detection of P and S wave arrival time.

Automatic Shear Wave Velocity Estimation in Bender Element Testing

Dynamic properties of soils, such as shear wave velocity and damping, are some of critical parameters in the design of civil infrastructures subjected to vibrations from earthquakes and machine foundations. Bender element (BE) testing is used in the laboratory to determine shear wave velocity; however, there is no standard procedure for the interpretation of the results. The main limitation in BE testing is the correct estimation of the shear wave arrival time leading to uncertainty in the values of shear wave velocity. In this paper, three different automatic methods for the shear wave arrival time detection were tested. From these methods, a new procedure was proposed for the automatic determination of the shear wave arrival time using the Akaike information criterion. The method is tested on a series of bender element measurements giving less than 5 % error when the results were compared with the standard method for a signal-to-noise ratio higher than four.

Seismic tomography and anisotropy of the Helan‐Liupan tectonic belt: Insight into lower crustal flow and seismotectonics

AbstractWe determined detailed 3‐D P and S wave velocities (Vp and Vs) and Poisson's ratio (σ) images as well as P wave azimuthal anisotropy in the crust and uppermost mantle beneath the Helan‐Liupan tectonic belt (HLTB) and adjacent regions. The data set used in this study consists of 38,880 P wave and 35,117 S wave arrival times from 5028 local earthquakes recorded by 66 seismic stations in the study area during 1980 to 2014. Obvious low‐Vp and low‐σ anomalies are revealed in the lower crust beneath the Qilian Orogenic Belt and Western Qinling, which we interpret as a weakened zone mainly caused by water and capable of ductile flow on a geological timescale. Our P wave anisotropy results suggest that the flow direction in the lower crust is nearly parallel to the direction of the geodetic crustal motion and that of the upper mantle flow beneath the study region. Most of the 26 large historical earthquakes (1125–1954) in the study region occurred in the boundary zones where Vp, Vs, and σ change drastically over a short distance. Beneath the source areas of the large historical earthquakes, fluid‐related low‐velocity zones exist widely in the lower crust. The fluids result from dehydration of hydrous minerals in the deeper crust and uppermost mantle beneath the northeastern Tibetan Plateau. When the fluids migrate upward to the active faults, the fault zone friction is reduced and so large crustal earthquakes can be triggered. Our present results shed new light on the seismogenesis and geodynamics of the northeastern Tibetan Plateau and adjacent areas.