Apparent Velocity Research Articles

Robust depletion shutdown guidance algorithm for long-range vehicles with a solid divert control system in large deviation conditions

To address the problem of depletion shutdown precise guidance for a long-range vehicle in large deviation condition, an online guidance algorithm based on Bezier curves and zero-range orientation (ZRO) is proposed under the conditions of thrust magnitude deviation, thrust direction deviation, mass flow rate deviation, and depletion shutdown time deviation of the solid divert control system. First, the mapping relationship between the apparent velocity to be gained (AVTG) and the impact deviation is analyzed based on the variational principle. The AVTG is solved with the Newton iterative method in the designed AVTG solution plane. Then, in the plane spanned by the AVTG and the ZRO, the key parameters of the Bezier curve are solved to obtain the Bezier energy management curve by taking the apparent acceleration direction and the angular velocity of the energy management terminal as the ZRO and zero, respectively, as constraints, which effectively reduces the influence of the solid divert control system performance parameter perturbation. Finally, the feedback linearization method is applied to track the Bezier energy management curve. A detailed simulation experiment is designed to analyze the advantages and computational complexity of the proposed algorithm. The Monte Carlo simulation results show that the proposed algorithm has high precision and good robustness, and the 3σ error of the proposed algorithm is 2.58 m. On the STM32F407 single-chip microcomputer, the proposed algorithm takes 25.38 ms, which demonstrates good real-time performance and a certain engineering application value.

Synthetic radio images of structured GRB and kilonova afterglows

ABSTRACT In this paper, we compute and analyse synthetic radio images of gamma-ray bursts (GRBs) and kilonova afterglows. For modelling the former, we consider GRB170817A-inspired set of parameters, while for the latter, we employ ejecta profiles from numerical-relativity simulations. We find that the kilonova afterglow sky map has a doughnut-like structure at early times that becomes more ring-like at late times. This is caused by the fact that the synchrotron emission from electrons following Maxwellian distribution function dominates the early beamed emission, while emissions from electrons following power-law distribution is important at late times. For an on-axis observer, the image flux centroid moves on the image plane, initially away from the observer. The image sizes, we find, are the largest for equal mass merger simulations with the soft equation of state. The presence of a kilonova afterglow affects the properties inferred from the source sky map, even if the GRB afterglow dominates the total flux density. The main effect is the reduction of the mean apparent velocity of the source, and an increase in the source size. However, this effect becomes negligible around the light curve peak of the GRB afterglow. For a far off-axis observer, neglecting the presence of the kilonova afterglow may lead to systematic errors in the inference of GRB properties from the sky map observations. Notably, at the observing angle inferred for GRB170817A, the presence of kilonova afterglow would affect the sky map properties, only at very late times $t\gtrsim 1500\,$ d.

Analysis of the riverbed backscattered signal registered by ADCPs in different bedload transport conditions – field application

Acoustic Doppler current profilers (ADCP) were deployed to investigate the backscattering (BS) signal in three navigable rivers, in different bedload transport conditions. This study aims to demonstrate that the BS strength, as an additional variable to the apparent bedload velocity, improves the characterization of the bedload transport using ADCPs. The M9 –3 MHz and the vertical beam M9 – 0.5 MHz showed decline of the BS strength as the bedload intensity increased, whereas the RDI –1.2 MHz was relatively insensitive. The correlation between the median grain size and the BS strength for the 0.5 MHz was linear, for the 3 MHz the BS strength was attenuated in the active layer, and for 1.2 MHz, it revealed a parabolic distribution. Moreover, the analyses of the ADCP measured variables, using wavelet transformations and unsupervised machine learning, highlighted the importance of the spatial and temporal variance and transient nature of the bedload transport.

A VLBI Proper Motion Analysis of the Recoiling Supermassive Black Hole Candidate Mrk 1018

Mrk 1018 is a nearby changing-look active galactic nucleus (AGN) that has oscillated between spectral Type 1.9 and Type 1 over a period of 40 yr. Recently, a recoiling supermassive black hole (rSMBH) scenario has been proposed to explain the spectral and flux variability observed in this AGN. Detections of rSMBHs are important for understanding the processes by which SMBH binaries merge and how rSMBHs influence their galactic environment through feedback mechanisms. However, conclusive identification of any rSMBHs has remained elusive to date. In this paper, we present an analysis of 6.5 yr of multifrequency Very Long Baseline Array monitoring of Mrk 1018. We find that the radio emission is compact down to 2.4 pc, and it displays flux density and spectral variability over the length of our campaign, typical of a flat-spectrum radio core. We observe proper motion in RA of the radio core at −36.4 ± 8.6 μas yr−1 (4.2σ), or 0.10c ± 0.02c at the redshift of Mrk 1018. No significant proper motion is found in DEC (31.3 ± 25.1 μas yr−1). We discuss possible physical mechanisms driving the proper motion, including an rSMBH. We conclude that the apparent velocity we observe of the VLBI radio core is too high to reconcile with theoretical predictions of rSMBH velocities and that the proper motion is most likely dominated by an unresolved, outflowing jet component. Future observations may yet reveal the true nature of Mrk 1018. However, our observations are not able to confirm it as a true rSMBH.

Study on prediction model of liquid holdup based on back propagation neural network optimized by tuna swarm algorithm

ABSTRACT It is unavoidable that there will be liquid accumulation in the low-lying areas of the pipelines during the operation of wet gas pipelines. The existence of liquid accumulation can generate a variety of safety issues and, in extreme circumstances, accidents. The accurate calculation of liquid holdup in gas-liquid two-phase flow is of great significance for the study of flow pattern identification, pressure drop calculation, pigging cycle determination, hydrate prediction, wax deposition prediction, pipeline corrosion evaluation and prediction, and transportation efficiency calculation of gas pipelines. Therefore, it is crucial to predict the liquid holdup of wet gas pipelines. 2141 independent experimental data samples were collected and screened out from literatures. Based on the gray theory, gray relation analysis was carried out on the influencing factors of liquid holdup, and the factors with greater influence were selected as the influencing variables; the liquid holdup prediction model based on tuna swarm algorithm optimized BP neural network was established, with pipe diameter, inclination angle, apparent gas velocity, apparent liquid velocity, average temperature, average pressure, and liquid viscosity as input parameters, and liquid holdup as output parameter. Liquid holdup was predicted for upward inclined, downward inclined, and horizontal pipelines respectively. The results show that the prediction model of liquid holdup established in this paper has high accuracy, with the MAPE value of 5.3223%, RMSE value of 0.0213, and R 2 value of 0.9924 for upward inclined pipelines; the MAPE value of 10.1859%, RMSE value of 0.0174, and R 2 value of 0.9922 for downward inclined pipelines; the MAPE value of 4.8037%, RMSE value of 0.0113, and R 2 value of 0.9974 for horizontal pipelines. The predicted results are generally stable and have a wider scope of application, providing a new idea and approach for predicting the liquid holdup of wet gas pipelines.

Added mass and damping forces of a floating tidal turbine undergoing pendulum motion

Many commercial engineering software programmes used to design floating tidal turbines neglect the added mass and damping because most of the code considers floating wind turbine designs, which is acceptable since air is significantly less dense than seawater. However, added mass and damping forces are important parameters that need to be included in the design of a floating tidal turbine. The increase in instantaneous time-dependent loading and changes in the natural frequency of a floating tidal turbine make these hydrodynamic forces non-negligible, especially for large turbines. The present study describes the construction of matrices of added mass and damping that can be used as inputs to simpler engineering models. These matrices were constructed by conducting three-dimensional blade-resolved CFD simulations for a floating tidal turbine operating under a prescribed pitch motion (i.e., pendulum-like motion) under various motion amplitudes and frequencies. The added mass and damping were also empirically extracted from the fluctuating thrust force, the empirical model derivation of which is given in this paper. Higher motion amplitude and frequency increase the pressure on rotor blades, which increases the amplitude of loading variations. A floating tidal turbine's mean power and thrust deviate from that of a stationary turbine due to suboptimal rotor operating conditions caused by the change in tip speed ratio (which is due to the apparent velocity variation). Formulations can be constructed (as functions of motion amplitude and frequency) to calculate added mass and damping forces based on the data of hydrodynamic forces provided in this paper, which can be applied to a conventional turbine design model. The added mass and damping forces increase the overall mass and damping of the floating rotor, respectively, which affects the motion and loading of the device.

Monitoring induced microseismicity in an urban context using very small seismic arrays: The case study of the Vendenheim EGS project

Monitoring the seismicity induced by fluid injections in deep geothermal reservoirs is often limited by the significant anthropogenic ambient noise level inherent to most enhanced geothermal system (EGS) projects in urban contexts. We report on the performance of a monitoring network made of three small aperture (72 m) seismic arrays composed of 21 3D nodes. We test the setup for four months (from 12 December 2020 to 8 April 2021) of the Strasbourg sequence of induced earthquakes (2019–2022) related to the EGS Georhin project (Vendenheim, France). The deployment starts a few days after the MLv = 3.6 induced earthquake of 4 December 2020 and covers the early shut-in period of the wells. We use a beamforming technique to characterize the main noise sources, which consist of slow apparent velocities of surface waves emitted from mobile anthropogenic sources (motorway and railway traffic). We detect events with a phase-weighted stacking method, which is efficient when wavefronts illuminate the arrays with a high apparent velocity. Earthquakes associated with these detections are located using a matched field processing technique. The obtained catalog includes 216 seismic events, which represent four times more events than the reference catalog from Le Bureau Central Sismologique Français–Renass (the national academic agency in charge of seismicity monitoring in France), and a reduction of the completeness magnitude from 0.3 to −0.5. The clustering of the seismicity is analyzed using waveform correlation. The enriched catalog reveals intermittent seismic activity during the slow and continuous decrease in fluid pressure after shut-in.

Observation of Shallow Slow Earthquakes by Distributed Acoustic Sensing Using Offshore Fiber‐Optic Cable in the Nankai Trough, Southwest Japan

AbstractOff Cape Muroto area, along the Nankai Trough in southwest Japan, is a typical area with adjacent occurrences of slow and megathrust earthquakes. High‐resolution monitoring of slow earthquakes is necessary to understand tectonic conditions. In the off Muroto area, distributed acoustic sensing (DAS) measurement, which provides high‐density strain data, has been conducted using offshore fiber‐optic cable. We observed shallow tremors, a type of slow earthquakes, using DAS measurement for the first time. The characteristics of the tremor signals recorded by DAS were longer durations than those recorded in seismographs and composed of several phases with apparent velocities of several hundreds of m/s to several km/s that are coherent only in tens of meters. By combining DAS and seismograph data, we located these tremors around a subducted seamount peak. Therefore, spatial relationship between slow earthquakes and structural characteristics is suggested. This is a pioneering study of slow earthquake observation using DAS.

Seismic velocity structure of the crust and uppermost mantle beneath the Tien Shan and its adjacent areas

The Tien Shan and its adjacent areas have been a prime place to understand the process of continental collision, the mechanism of mountain building and the interaction of tectonic blocks. In this study, we collect seismic data recorded by 74 broad-band stations from the China Provincial Digital Seismic Networks and the Regional Kyrgyzstan and Kazakhstan Networks between January, 2007 and September, 2009. A joint inversion technique that combines three types of datasets (receiver functions, phase velocities of Rayleigh wave measured from both ambient noise and teleseismic earthquake data) is applied to image the crustal and upper mantle structure beneath the Tien Shan and its adjacent areas. The average crustal thickness in the study area is about 50 km, however, the Moho depth extends to ∼70 km beneath the Kyrgyz Platform near the southwestern Tien Shan. Our velocity models show a good correlation with subsurface geological features at shallow depths: low velocities are predominantly observed beneath the basins due to thick sedimentary layer, whereas high velocities are mainly distributed beneath the mountain ranges due to crystalline basement rocks. In the upper mantle a low velocity zone is obviously observed beneath the western Tien Shan. Both the crust thickness and S wave velocity structure of the Tien Shan and its adjacent regions display obvious horizontal and vertical heterogeneities from west to east, which suggests that the far-field effects of the collision between Eurasian plate and Indian plate plays an important role in the tectonic activity of the Tien Shan. The apparent velocity heterogeneities beneath the northern Tarim Basin may indicate that the Tarim Basin may have been eroded and damaged by upwelling hot materials from the upper mantle.

Higher Apparent Gas Transfer Velocities for CO2 Compared to CH4 in Small Lakes.

Large greenhouse gas emissions occur via the release of carbon dioxide (CO2) and methane (CH4) from the surface layer of lakes. Such emissions are modeled from the air-water gas concentration gradient and the gas transfer velocity (k). The links between k and the physical properties of the gas and water have led to the development of methods to convert k between gases through Schmidt number normalization. However, recent observations have found that such normalization of apparent k estimates from field measurements can yield different results for CH4 and CO2. We estimated k for CO2 and CH4 from measurements of concentration gradients and fluxes in four contrasting lakes and found consistently higher (on an average 1.7 times) normalized apparent k values for CO2 than CH4. From these results, we infer that several gas-specific factors, including chemical and biological processes within the water surface microlayer, can influence apparent k estimates. We highlight the importance of accurately measuring relevant air-water gas concentration gradients and considering gas-specific processes when estimating k.

Seismic Phenomena Associated with the Eruption of a Volcano in the Area of the Tonga Archipelago on January 15, 2022

The study of changes in the seismic process associated with the eruption and the assessment of the energy parameters and structure of the wave field from seismic data is the subject of this work. Three types of disturbances are distinguished in the structure of the wave field. First of all, these are Rayleigh surface waves with an average oscillation period of 23 s, well traceable at distances up to 100 degrees. The group velocity of Rayleigh waves is 3.6–3.8 km/s. The magnitude calculated from them at stations mainly with oceanic propagation paths is Ms = 5.52 ± 0.18, and the corresponding seismic energy was on the order of Ec = (1–7) × 1013 J, and the scalar seismic moment M0 =2.4 × 1017 J. Two other types of oscillations were detected on seismic channels with a frequency band from 0.0003 to 0.1 Hz of the stations. For the first, the apparent velocity of propagation of the disturbance lies in the range of 0.28–0.37 km/s with a characteristic period of 268 s. This type of disturbance is associated with the gravitational response of the seismometer to an acoustic disturbance in the atmosphere. For the second type of seismic disturbances, the propagation velocity is 0.21–0.28 km/s with characteristic periods of 450 s on the horizontal components of seismic receivers. This type of seismic disturbance is probably caused by the interaction of the gravitational wave in the hydrosphere with the coast of the islands on which the seismic stations are located.

Mildly relativistic motion in the radio-quiet quasar PG 1351+640

ABSTRACT Measuring the proper motion of the emission component in radio-quiet quasars (RQQs) could help to distinguish between the origins of the radio emission and to understand whether the jet production mechanism is the same in radio-loud quasars and RQQs. PG 1351+640 is one of the few RQQs suitable for proper motion studies: it has two compact components on milli-arcsec scales, a flat-spectrum core and a steep-spectrum jet; both components are ≳2 mJy at 5 GHz and are well suited for Very Long Baseline Array (VLBA) observations. We compare recent VLBA observations with that made seventeen years ago and find no significant change in the core-jet separation between 2005 and 2015 (a proper motion of 0.003 mas yr−1). However, the core-jet separation increased significantly between 2015 and 2022, inferring a jet proper motion velocity of 0.063 mas yr−1, which corresponds to an apparent transverse velocity of $0.37\, c$ . The result suggests that the jet of the RQQ PG 1351+640 is mildly relativistic and oriented at a relatively small viewing angle.

Ultra-high-resolution observations of plasmoid-mediated magnetic reconnection in the deep solar atmosphere

Context. Magnetic reconnection in the deep solar atmosphere can give rise to enhanced emission in the Balmer hydrogen lines, a phenomenon referred to as Ellerman bombs. Aims. To effectively trace magnetic reconnection below the canopy of chromospheric fibrils, we analyzed unique spectroscopic observations of Ellerman bombs in the Hα line. Methods. We analyzed a 10 min data set of a young emerging active region observed with the prototype of the Microlensed Hyperspectral Imager (MiHI) at the Swedish 1-m Solar Telescope (SST). The MiHI instrument is an integral field spectrograph that is capable of achieving simultaneous ultra-high resolution in the spatial, temporal, and spectral domains. With the combination of the SST adaptive optics system and image restoration techniques, MiHI can deliver diffraction-limited observations if the atmospheric seeing conditions allow. The data set samples the Hα line over 4.5 Å with 10 mÅ pix−1, with 0.​​″065 pix−1 over a field of view of 8.​​″6 × 7.​​″7, and at a temporal cadence of 1.33 s. This constitutes a hyperspectral data cube that measures 132 × 118 spatial pixels, 456 spectral pixels, and 455 time steps. Results. There were multiple sites with Ellerman bomb activity associated with strong magnetic flux emergence. The Ellerman bomb activity is very dynamic, showing rapid variability and a small-scale substructure. We found a number of plasmoid-like blobs with full-width-half-maximum sizes between 0.​​″1 and 0.​​″4 and moving with apparent velocities between 14 and 77 km s−1. Some of these blobs have Ellerman bomb spectral profiles with a single peak at a Doppler offset between 47 and 57 km s−1. Conclusions. Our observations support the idea that fast magnetic reconnection in Ellerman bombs is mediated by the formation of plasmoids. These MiHI observations demonstrate that a microlens-based integral field spectrograph is capable of probing fundamental physical processes in the solar atmosphere.

Comparing two methods of acquiring stable fluidization state for binary particles during measurement of segregation

Co-fluidization of two types of particles is commonly encountered in the chemical and energy industry. A deep understanding of segregation between them is of great significance. The accurate measurement of segregation for any gas velocity (Ug) from the experimental perspective is the first and critical step. The key lies in acquiring the stable fluidization state that could represent the given Ug. Two distinct methods were thoroughly compared in this work. The first was decreasing gas flow quickly from high values to the target Ug and keeping fluidization therein for sufficient time. The second was reducing gas flow very slowly from high values to the target Ug. The apparent minimum fluidization velocity of the binary particles was denoted as Umfa whereas the minimum fluidization velocities of flotsam and jetsam were represented by UmfF and UmfJ. When Ug was greater than UmfJ, the corresponding stable fluidization state could be easily reached via either method. Yet, it could only be acquired via the second method for Ug∈(Umfa, UmfJ). For Ug∈(UmfF, Umfa), neither method was feasible. The difficulty in acquiring the stable fluidization state for Ug < UmfJ resulted eventually from the internal friction among the particles, due to which the de-fluidization of some jetsam particles could deprive the capability of many other particles to move and hinder their migration to the stable equilibrium positions. The macroscopic state of binary particles at Ug∈(UmfF, UmfJ) was further found to depend also on the path taken to reach it; binary particles therein could have different equilibrium states (being polymorphic); the final fluidization state acquired via the first method was demonstrated to be metastable. The stable fluidization state of binary particles at Ug∈(UmfF, Umfa) was too complicated to describe; convincing methods for acquiring it and determining the true extent of segregation are of urgent need; the second method was still effective in approaching the so-called stable fluidization state.

Infrasound waves and sulfur dioxide emissions caused by the 2022 Hunga volcanic eruption, Tonga

A powerful volcanic eruption that occurred in Tonga on 15 January 2022, produced strong vibrations in the atmosphere, ocean, and solid Earth. We identify infrasound waves traveling with an apparent velocity of 0.31 km/s up to 10,000 km from Tonga in seismic and tsunami recordings. Clear signals of these infrasound waves with a fundamental model of Lamb wave are evident before the shallow-water gravity wave and after the Rayleigh and body waves. The pressure amplitudes of the infrasound waves at stations of 400–1000 km from the eruption are 5–10 hPa. The infrasound wave generated trans-Pacific tsunami waves to arrive 4–5 h earlier than the gravity waves of regular tsunami in the populated countries near the Pacific oceans. We use numerical simulation methods for the oceanic plate subduction zone in Tonga to estimate the pressure-temperature fields and the desulfurization at shallow depths. The simulated total sulfur dioxide released during the eruption ranges from 0.4 to 2.0 Tg. This is small in comparison with previous studies of comparable infrasound pressures. The total emission and sulfur dioxide amounts may have been controlled by the amount of sulfur contained in the subducted plate as well as the pressure and temperature conditions of the subduction zones.

Axial transmission technique for screening bucked shin in a horse leg

For the safe and simple screening of equine leg bones, we applied an ultrasonic axial transmission (AT) technique to an equine bone sample with a weak bucked shin. Both experimental and simulation studies have been conducted. To simulate by the finite-difference time-domain method, a digital model of the equine leg bone was fabricated. The experimental and simulation results showed a similar tendency. The obtained apparent wave velocities in the axial direction were almost constant in the healthy part but strongly fluctuated in the bucked shin part because of the small surface irregularities. The standard deviation values of the wave velocities in the bucked shin parts were large. These results indicate that a weak bucked shin in the equine leg bone may be screened clinically by a simple evaluation of velocity fluctuation using the AT technique.

Volume flow rate calculation model of non-full pipe multiphase flow based on ultrasonic sensors

In the oil and gas industries, it is crucial to employ appropriate drilling fluids in order to maintain equilibrium of formation pressure throughout the various stages of drilling operations. During the recycling process, the drilling fluid may precipitate gas and as a result exhibit non-full pipe flow upon return to the surface. Accurate measurement of the volume flow rate of the drilling fluid is imperative in obtaining valuable information from the bottom of the well. Commonly, on-site drilling operations use a multiphase target flowmeter in conjunction with an empirical model to rectify calculation results. However, the returned multiphase flow that is not fully in the pipe and its liquid component exhibits corrosive properties, making it a challenge for traditional invasive measurement methods to achieve adequate accuracy over an extended period. Therefore, the theoretical potential of utilizing non-contact ultrasonic sensors for measuring the multiphase volume flow rate of the non-full pipe flow is significant. In this research, an apparent flow velocity calculation model was established by integrating the ultrasonic Doppler shift model and pipeline fluid mechanics utilizing a four-channel ultrasonic array. Subsequently, the invariant scattering convolution—long short-term memory) network was trained on the data-fused ultrasonic signal to identify the liquid level. The velocity-area method was also employed to establish a new multiphase volume flow calculation model. To evaluate the validity of the proposed model, comparison experiments of liquid single-phase flow and liquid–solid two-phase flow were conducted. The experimental results show that, compared with the comparative flow measurement system, the accuracy of the ultrasonic flow measurement system is reduced by 0.965%, the nonlinear error by 2.293%, the average relative error by 2.570%, the standard deviation by 1.395, and the root mean square error by 14.394.

Using Passing Trains as Seismic Sources for Refraction Microtremor Site Characterisation Surveys: Rugeley, Staffordshire, UK

Microtremor seismic surveys are routinely used to provide shear wave velocities that are converted to soil stiffness site profiles. In this paper, we look to assess the feasibility of using trains as seismic sources to characterize near-surface geology, define the optimum survey parameters to collect train-induced vibrations (i.e., array location and orientation to the railway) and find how the geology affects train-induced vibration characteristics. Three-component train-induced shear wave vibrations were recorded on short (44 m) and long (115 m) linear seismic arrays, both parallel and orthogonal to the nearby railway embankment, using standard seismic refraction recording equipment. The collected data were divided into short/long array size/orientation and seismic components for each survey configuration. 1D shear wave velocity-depth profiles were also generated for all data sets. Results showed thst long linear arrays with vertical components, parallel to the railway embankment, was optimal with the greater depth ranges. The vertical component amplitude of train-induced vibrations was found to be affected by the site geology, increasing with the thickening of Quaternary deposits and having different magnitudes for trains traveling in different directions. Results showed that different apparent shear-wave velocities were obtained from different train groups and different seismic components. The passenger trains (i.e. Virgin Trains Pendolino and British Midland 319 series) generate Rayleigh waves at higher frequencies than the freight trains.

Large variations of crustal thickness across the Taiwan orogeny constrained by Moho-refraction recorded by the Formosa Array

The Taiwan orogenic belt is formed by the strong convergence between the Philippine Sea Plate and the Eurasian Plate. The detailed mountain building process is still under debated largely due to the poor constraint of deep crustal structures, particularly the geometry at the Moho-depth. Here the Moho-refracted P waves are identified from the seismic data recorded by a dense seismic array (Formosa Array) in northern Taiwan. Although the refracted seismic energy is often weak at each individual station, the waveform similarity recorded at the nearby stations provides a reliable constraint for estimating the apparent velocity recorded by the dense seismic array. The forward modeling of the observed Moho-refracted P waves shows a larger crustal thickness (~ 52 km) beneath the Backbone Ranges than beneath the adjacent Hsuehshan Ranges (~ 36 km). Such a result is not only confirming the Moho variations along a few of the NW-SE profiles from the previous studies, but also showing the strong Moho variation is well extended along the NE-SW direction. The large change in the crustal thickness across the Taiwan orogeny strongly indicate that the orogenic deformation in Taiwan might extend beyond the shallow crust, possibly involving in the deep crust and upper mantle. The Taiwan orogeny may not be reaching to the isostatic equilibrium yet.

Occurrence Apparent Velocities for Identification and Quantification of Space–Time Clustering Precursory to a Large Earthquake. Application to Large (M &gt; 7.0) Earthquakes in Southern California and Northern Baja California

Occurrence Apparent Velocities for Identification and Quantification of Space–Time Clustering Precursory to a Large Earthquake. Application to Large (M &gt; 7.0) Earthquakes in Southern California and Northern Baja California