Estimation Of Source Parameters Research Articles

Compressive sensing multi-target diffusive source localisation using sparse recovery algorithms in sensor networks

According to the multi-target diffusive source localisation in sensor networks, a compressive sensing sparse recovery algorithm was proposed for the mismatching problem of the target sources sparsity and the high-dimensional redundant sampling signals. Firstly, the compressive sensing system model and the related terms were given and explained. Then, the joint optimal estimation of the sparse diffusive source vector and the diffusion distribution state were realised with the variational Bayesian expectation maximisation algorithm (VB-EM). In which, the dynamic compressive sensing dictionary model of the real target source sparse representation was designed and adjusted with the grid division parameters optimisation for the dictionary mismatch problem solving. Finally, the simulation results show that the proposed compressive sensing method with VB-EM algorithm could effectively achieve the diffusive source parameters estimation and its diffusion distribution state prediction. Compared with the traditional compressive sensing sparse recovery algorithms, it could obtain higher robustness performance for the rapid and accurate localisation in complex environment.

Compressive sensing multi-target diffusive source localisation using sparse recovery algorithms in sensor networks

According to the multi-target diffusive source localisation in sensor networks, a compressive sensing sparse recovery algorithm was proposed for the mismatching problem of the target sources sparsity and the high-dimensional redundant sampling signals. Firstly, the compressive sensing system model and the related terms were given and explained. Then, the joint optimal estimation of the sparse diffusive source vector and the diffusion distribution state were realised with the variational Bayesian expectation maximisation algorithm (VB-EM). In which, the dynamic compressive sensing dictionary model of the real target source sparse representation was designed and adjusted with the grid division parameters optimisation for the dictionary mismatch problem solving. Finally, the simulation results show that the proposed compressive sensing method with VB-EM algorithm could effectively achieve the diffusive source parameters estimation and its diffusion distribution state prediction. Compared with the traditional compressive sensing sparse recovery algorithms, it could obtain higher robustness performance for the rapid and accurate localisation in complex environment.

Study on the source parameters of the micro-earthquakes in Laohutai coal mine based on double difference relocation

Seismicity related to industrial mining activities needs to be understood and quantified in order to ensure safe mining operations. It is of great important to determine if the sources of such events follow the common models and theories, and determine the source rupture property and scale of such events. Moreover, the location of the source is very important to obtain the source parameters. For this purpose, we analyze 103 events recorded in the Laohutai coal mine that are related to fault structure and mining activities to determine their source properties based on relocation. Firstly, the 103 micro-earthquakes were relocated based on double difference algorithm. Then, the source parameters of seismic moment M0, source radius R, corner frequency f0, seismic attenuation Q, energy E, stress drop △σ and apparent stress σa are computed based on relocation, Brune model and grid-search method. The relationship between the other source parameters and seismic moment, the relationship between ML and Mw, and the influence of location on source parameters and magnitude are further analyzed. Finally, the difference of the source parameters between Laohutai coal mine, Qianqiu coal mine and natural earthquakes are analyzed. We find that the source location can be effectively corrected based on double difference algorithm; ω2 model is well suited to estimate source parameters of micro-earthquakes in the Laohutai coal mine. The source spectra show strong directivity effects. Stations in the rupture direction have higher corner frequencies, while stations away from rupture direction have lower corner frequencies. With the increase of M0, the source parameters of R, E and △σ basically show a linear increase, the source parameter f0 basically show a linear decrease and the apparent stress fluctuate up and down around a certain value as a whole. After relocation, the location of the source has a significant effect on the quality attenuation factor Q and has no obvious effect on other source parameters. The influence of relocation on moment magnitude and local magnitude is not obvious. The moment magnitude is linear with the local magnitude. Considering Mw, ML1 can relatively well be used to evaluate the magnitude of the earthquakes in Laohutai coal mine; For the micro-earthquakes with the same magnitude, the values of corner frequency, stress drop, apparent stress and energy in Qianqiu coal mine are greater than those in Laohutai coal mine, the value of source radius in Laohutai coal mine is greater than those in Qianqiu coal mine. For the events with the same magnitude, the corner frequency and the stress drop value of micro-earthquakes are smaller than those of natural earthquake. These indicate that the rupture properties and scales of micro-earthquakes in Laohutai coal mine are different from those of the micro-earthquakes in Qianqiu coal mine and natural earthquakes. The results help us to effectively evaluate the property and magnitude of microseismic source, and better understand causes and consequences of microseismicity in coal mine.

High-resolution source imaging based on time-reversal wave propagation simulations using assimilated dense seismic records

SUMMARY This paper describes an efficient approach to high-resolution time-reversal source imaging simulation. Dense seismograph network records are backpropagated from stations to the hypocentre through a 3-D subsurface structure model to estimate the initial source wavefield at the earthquake initiation time. By assimilating high-density observational data into the time-reversal wave propagation, a clearer source image can be determined, even for deep and distant earthquakes, than is achievable with conventional source imaging. The effectiveness of data-assimilation-based source imaging by a time-reversal wave propagation simulation with a 3-D heterogeneous structural model was demonstrated using recordings from a nationwide strong-motion seismograph network during the 2007 Off Niigata, Japan, Mw 6.6 earthquake, and the 2007 Off Ibaraki, Japan,Mw 6.8 earthquake. Such data-assimilated-based simulations are also effective for early forecasting of strong ground motions caused by large earthquakes through fast time-advancing simulations based on the current assimilated wavefield. We will discuss the feasibility of a disaster prevention system for the early forecasting of strong motion disasters due to large earthquakes, based on repeatedly estimating source parameters and forecasting strong motions in future time based on the current assimilated wavefields.

Dead Sea Earthquake-Source Scaling Using Masada Deep Borehole Data

AbstractThe low-noise environment in the Masada deep borehole (MDBI), an abandoned oil well on the western shore of the Dead Sea rift, allows the recordings of many small-magnitude earthquakes. MDBI has a 2 Hz triaxial seismometer installed at a depth of 1256 m below ground and 1516 m below sea level. We used MDBI P- and S-wave data and the general source relationship u(f)=u(0)e−(πft/Q)/[1+(f/f0)2y]1y, in which f0 is corner frequency and 1<y<2, to estimate source parameters for 1031 earthquakes along the Dead Sea fault. The seismic moments, corner frequencies, and source radii as determined by this model show a complete breakdown in earthquake scaling. The spectra of many small earthquakes are characterized by drop-offs of roughly f−2. Q0(P) and Q0(S) increase with event distances up to ∼25 km, beyond which they are ∼1510 and 2285 for p=1 and ∼2040 and 2985 for p=2. For these two end members, the ratio Q0(S)/Q0(P) for distances of 20–150 km has values ranging between 1.3 and 1.4. At shorter distances, this ratio is somewhat higher, indicating that P waves attenuate faster than S waves. The energy versus seismic moment results shows no azimuthal dependence, implying that it is a valid measure of source strength. For the end-member models, this relationship follows E∝M01.35 and E∝M01.49 for the P and S waves, respectively.

Modelling pyroclastic density currents from a subplinian eruption at La Soufri\xe8re de Guadeloupe (West Indies, France)

We have used a three-dimensional, non-equilibrium multiphase flow numerical model to simulate subplinian eruption scenarios at La Soufrière de Guadeloupe (Lesser Antilles, France). Initial and boundary conditions for computer simulations were set on the basis of independent estimates of eruption source parameters (i.e. mass eruption rate, volatile content, temperature, grain size distribution) from a field reconstruction of the 1530 CE subplinian eruption. This event is here taken as a reference scenario for hazard assessment at La Soufrière de Guadeloupe. A parametric study on eruption source parameters allowed us to quantify their influence on the simulated dynamics and, in particular, the increase of the percentage of column collapse and pyroclastic density current (PDC) intensity, at constant mass eruption rate, with variable vent diameter. Numerical results enabled us to quantify the effects of the proximal morphology on distributing the collapsing mass around the volcano and into deep and long valleys and to estimate the areas invaded by PDCs, their associated temperature and dynamic pressure. Significant impact (temperature > 300 °C and dynamic pressure > 1 kPa) in the inhabited region around the volcano is expected for fully collapsing conditions and mass eruption rates > 2 × 107 kg/s. We thus combine this spatial distribution of temperature and dynamic pressure with an objective consideration of model-related uncertainty to produce preliminary PDC hazard maps for the reference scenario. In such a representation, we identify three areas of varying degree of susceptibility to invasion by PDCs—very likely to be invaded (and highly impacted), susceptible to invasion (and moderately impacted), and unlikely to be invaded (or marginally impacted). The study also raises some key questions about the use of deterministic scenario simulations for hazard assessment, where probability distributions and uncertainties are difficult to estimate. Use of high-performance computing techniques will in part allow us to overcome such difficulties, but the problem remains open in a scientific context where validation of numerical models is still, necessarily, an incomplete and ongoing process. Nevertheless, our findings provide an important contribution to the quantitative assessment of volcanic hazard and risk at La Soufrière de Guadeloupe particularly in the context of the current unrest of the volcano and the need to prepare for a possible future reawakening of the volcano that could culminate in a magmatic explosive eruption.

Surface deformation of the Barren Island volcano, Andaman Sea (2007–2017) constrained by InSAR measurements: Evidence for shallow magma reservoir and lava field subsidence

Barren Island, situated in the Andaman Sea, is the northernmost active volcano of the Sunda arc. The oldest known eruption of the volcano was during the period 1787–1832. After about 150 years of quiescence, volcanic activity resumed in 1991 and continues since then. The magmatic plumbing system of this volcano is largely unknown due to lack of geophysical experiments owing to its remote location. We report, for the first-time, time-series surface deformation measurements of Barren Island volcano from interferometric synthetic aperture radar (InSAR) during epochs 2007–2011 and 2015–2017. Line-of-Sight (LOS) deformation of −50 mm/yr during 2007–2011 at the cinder cone is interpreted as the co-eruptive pressure changes associated with the 2008–2010 eruptions. Bayesian inversion suggests a shallow magma reservoir at a depth of 578−100+300 m below the summit. The depth of the magma reservoir is shallower than that of other volcanoes of the Sunda arc, probably due to the extensional stress regime imposed by the oblique subduction. Based on the present studies and previous works, we propose a plausible source model for Barren Island volcano. We also discuss potential biases in the present source parameter estimation due to the lack of high quality InSAR data from both ascending and descending directions. Significant deformation (−15 to −150 mm/yr) observed along the lava delta of Barren Island volcano for both the epochs are interpreted as post-emplacement subsidence of the lava flow. Further, we characterise the lava flow including volcanic deposits by mapping its spatial extent and elevation changes during 1979–2000 and 2000–2017 periods using geodetic measurements.

Estimation of Source Parameters of Local Earthquakes Based on Inversion of Waveform Data

Estimation of Source Parameters of Local Earthquakes Based on Inversion of Waveform Data

Modelling high-frequency seismograms at ocean bottom seismometers: effects of heterogeneous structures on source parameter estimation for small offshore earthquakes and shallow low-frequency tremors

SUMMARY The source characteristics of offshore seismic events, especially regular (or fast) and slow earthquakes, can provide key information on their source physics and frictional conditions at the plate boundary. Due to strong 3-D heterogeneities in offshore regions, such as those relating to sea water, accretionary prism and small-scale velocity heterogeneity, conventional methods using a 1-D earth model may mis-estimate source parameters such as the duration and radiation energy. Estimations could become severe inaccuracies for small offshore seismic events because high-frequency (>1 Hz) seismograms, which are strongly affected by 3-D heterogeneities, are only available for analysis because of their signal-to-noise ratio. To investigate the effects of offshore heterogeneities on source parameter estimation for small seismic events, we analysed both observed and simulated high-frequency seismograms southeast off the Kii Peninsula, Japan, in the Nankai subduction zone. Numerical simulations of seismic wave propagation using a 3-D velocity structure model clarified the effects of each heterogeneity. Comparisons between observations and model simulations demonstrated that the thick low-velocity accretionary prism has significant effects on high-frequency seismic wave propagation. Especially for shallow low-frequency tremors occurring at depths just below the accretionary prism toe, seismogram durations are significantly broader than an assumed source duration, even for stations with epicentral distances of approximately 10 km. Spindle-shape seismogram envelopes were observed even at such close stations. Our results suggest that incorporating 3-D heterogeneities is necessary for practical estimation of source parameters for small offshore events.

Reliability of Source Parameters for Small Events in Central Italy: Insights from Spectral Decomposition Analysis Applied to Both Synthetic and Real Data

ABSTRACTWe apply a spectral decomposition approach to isolate the source spectra from propagation and site effects and, in turn, to estimate the source parameters of small-to-moderate earthquakes that occurred in central Italy. The data set is composed of about 400,000 waveforms relevant to 4111 earthquakes in the moment magnitude range 1.5–6.5, recorded by a high-density network of stations installed in the study area. We first investigate the reliability of the source parameters for small magnitudes through numerical simulations. We generate synthetic spectra for different source scaling models and near-surface attenuation effects, considering the source–station geometry and the data availability of the central Italy data set. Our analysis with synthetics shows that the spectral decomposition is effective in isolating the source contributions from other factors. Moreover, the analysis of the residual distributions suggests that moment magnitude 1.8 is the lower bound for the retrieval of reliable Brune’s source parameters, although we observe an increase of residual’s variability below magnitude 3, and the estimated source parameters could be biased below magnitude 2.3. Remarkably, the assessment of the stress drop Δσ for small events is strongly hampered by site-specific attenuation near the surface. In view of the results with synthetics, we analyze the source parameters of earthquakes recorded in central Italy. The corner frequency versus seismic moment relationship describes a source scaling in which Δσ increases with increasing moment magnitude Mw, the mean Δσ varying from 0.1 MPa for Mw<2 to 7.9 MPa for Mw>5. In particular, Δσ increases mainly for Mw in the ranges 2.5–3 and 4.5–5.2. The corner frequencies estimated from the apparent source spectra do not show any dependence on hypocentral distance and magnitude, confirming that uncorrected anelastic attenuation effects do not significantly bias the results.

Model sensitivities in the case of high-resolution Eulerian simulations of local tephra transport and deposition

Tephra transport modelling has predominantly been carried out over synoptic-scale resolutions, resolving only fundamental atmospheric circulations. Consequently, model sensitivity studies have focused on these resolutions. In recent years, improved eruption source parameter (ESP) estimation methods and computational efficiency have progressively led to the use of higher resolutions to increase the fidelity of tephra transport simulations. This is a new computational regime whose model sensitivities remain largely unexplored. Here, high-resolution simulations using a 300 m horizontal grid spacing were carried out using WRF and FALL3D to assess sensitivity to: meteorological input data (using both reanalysis and forecast data), boundary layer parametrisation, plume model, settling velocity, total grain-size distribution (TGSD), and aggregation, leading to a total of 1280 possible configurations. An eruption that occurred on 28 July 2019 at Sakurajima volcano, Japan, is used as a case study, as the northwards dispersal of a 3.8 km-high plume led to the temporary closure of Kagoshima airport. Sedimentation was observed at three optical disdrometers on the volcano, providing insight on the deposition timing and particle size distribution. Results reveal that meteorological input data can have a significant impact over the fidelity of the simulations, with errors changing over one order of magnitude depending on the initialisation dataset. This was found to be the result of local bias in the simulated wind fields over the region of dispersal, which was not represented in the domain-wide assessment of the WRF simulations. Ensemble simulations using different meteorological input data were found to mitigate this, significantly increasing the fidelity of the final ensemble product. Use of a plume model and the correct estimation of the TGSD were seen to significantly improve results. Finally, even with detailed data to inform the choice, use of an empirical aggregation scheme was seen to significantly degrade the accuracy of the simulations.

Prospects for improving the sensitivity of the cryogenic gravitational wave detector KAGRA

Upgrades to improve the sensitivity of gravitational wave detectors enable more frequent detections and more precise source parameter estimation. Unlike other advanced interferometric detectors such as Advanced LIGO and Advanced Virgo, KAGRA requires different approach for the upgrade since it is the only detector which employs cryogenic cooling of the test masses. In this paper, we describe possible KAGRA upgrades with technologies focusing on different detector bands, and compare the impacts on the detection of compact binary coalescences. We show that either fivefold improvement in the $100 M_{\odot}$--$100 M_{\odot}$ binary black hole range, a factor of 1.3 improvement in the binary neutron star range, or a factor of 1.7 improvement in the sky localization of binary neutron stars is well feasible with upgrades that do not require changes in the existing cryogenic or vacuum infrastructure. We also show that twofold broadband sensitivity improvement is possible by applying multiple upgrades to the detector.

Estimates of plume height from infrasound for regional volcano monitoring

Present efforts in volcano monitoring, particularly in Southeast Asia, rely on the combination of local data (generally gathered at less than 100 km from the volcano), and satellite remote sensing. While this combination has its strengths, there are still weaknesses that the use of ground-based remote sensing data - such as distant infrasound measurements - could help alleviate. Infrasound offers tools for detecting and characterizing volcanic plumes independent of cloud cover and time of day. Larger volcanic eruptions generate infrasound that is related to the plume and offers a unique view into eruption dynamics within the context of monitoring. Past research has demonstrated that infrasound can be used to estimate source parameters, such as the rate at which material is ejected from volcanic vents during eruptions; these are key input parameters into empirical and numerical models to estimate the height of volcanic plumes, atmospheric ash transport and dispersion. Here, we demonstrate the use of remote infrasound in estimating the height of volcanic plumes, including a case study on the May 30, 2014 plume from the volcano Sangeang Api in Indonesia. We were able to determine the plume height using infrasound gathered from 2000 to over 5000 km distance from the volcano. During the January 2020 eruption of Taal volcano in the Philippines, this method was applied to remote infrasound recorded 1650 km to the east. We show that our workflow can be implemented in near real-time, offering an effective tool for rapid plume height measurement, including associated uncertainties, when volcanic clouds are not visible from the ground or space.

A Study on the Largest Hydraulic-Fracturing-Induced Earthquake in Canada: Observations and Static Stress-Drop Estimation

ABSTRACTOn 17 August 2015, an Mw 4.6 earthquake occurred northwest of Fort St. John, British Columbia, possibly induced by hydraulic fracturing (HF). We use data from eight broadband seismometers located ∼50 km from the hypocenter to detect and estimate source parameters of more than 300 events proximal to the mainshock. Stress-drop values estimated using seismic moment and corner frequency from single-event spectra and spectral ratios range from ∼1 to 35 MPa, within the typical range of tectonic earthquakes. We observe an ∼5-day delay between the onset of fluid injection and the mainshock, a b-value of 0.78 for the sequence, and a maximum earthquake magnitude larger than the prediction based on the total injection volume, suggesting that the Mw 4.6 sequence occurred on a pre-existing fault and that the maximum magnitude is likely controlled by tectonic conditions. Results presented here show that pre-existing fault structures should be taken into consideration to better estimate seismic hazard associated with HF operations and to develop schemes for risk mitigation in close proximity to HF wells.

Resolvability of the Centroid‐Moment‐Tensors for Shallow Seismic Sources and Improvements From Modeling High‐Frequency Waveforms

AbstractShallow earthquakes in the depth range 0–30 km make up more than 60% of all world's earthquakes. However, resolving their seismic source parameters such as the depth and moment tensor components presents a challenge. Here, we investigate the effect of frequencies higher than 0.025 Hz on centroid‐moment‐tensor inversion for the earthquakes occurring in the top 10 km of the Earth's crust. For a synthetic source located at the depth of 1 km, the maximum amplitude of ground motion due to a vertical dip‐slip mechanism from the waveforms filtered at 0.01–0.15 Hz is about 1,400 times larger than that filtered at 0.01–0.025 Hz. We quantify the effect of this dramatic difference and other waveform differences by introducing the “balance of amplitudes” and “waveform similarity” functions for different depths and frequencies. They present a simple and fast way to estimate the resolvability of seismic sources at a given depth and frequency band. For the 20 May 2016, Mw = 5.9 Petermann Ranges earthquake in Central Australia analyzed at 0.01–0.025 Hz, a high uncertainty accompanies the estimated source parameters. When the frequency band is 0.01–0.15 Hz, the centroid depth is well constrained at 1 km and the mechanism is a thrust fault striking ~314°N and dipping ~30°NE. These simulations require accurate Earth models. Our result, obtained at higher frequencies, is in a great agreement with various other studies that have been carried out for this earthquake and confirms a 20‐km long, shallow rupture.

Complex tectonic deformation in Circum-Tanzania Craton: East African Rift System

The reliable source parameters, the current deformation associated to the earthquakes and the current deformation in relationship with dynamic change of Victoria plate rotation are generally poorly understood owing to the lack of the proper techniques used in the Circum-Tanzania Craton. Therefore, the reliable estimated source parameters and the detail interpretation are very crucial. Here, moment tensor inversion is made from broadband seismic data for five earthquakes that occurred in the region in the years 2014 and 2016 with magnitude ranging from Mw 4.1 to 5.7. The 2014 sequence comprises four earthquakes where two of them occurred north of Kondoa with purely normal faulting mechanisms following the N–S oriented rift structure. The other two earthquakes from the 2014 group occurred north of Dodoma and are found to be normal faulting with significant strike-slip component with dextral sense of motion trending in the NW-SE direction which seems to agree with fault structure and aftershock distribution. On the other hand, focal mechanism of the 2016 earthquake in Kagera region with magnitude Mw 5.7 shows dominantly normal faulting trending WNW-ESE with strike-slip component and dextral sense of motion. The interpreted fault orientation for the Kagera earthquake seems to agree with macroseismic information and aftershock distribution which were recorded by seismic stations deployed immediately after the main shock (Mulibo, 2019). We therefore find that the observed normal, strike-slip and oblique slip deformation seems to be influenced by the extensional stress regime of the East African Rift System and the anti-clockwise rotation of the Victorian plate. On the other hand, it is not uncommon to observe deactivation of the NW-SE oriented weak zones in the East African Rift System which seems to agree with our fault mechanism results. In addition, the waveform inverted depths of the studied earthquakes vary from 12 to 26 km in the Circum-Tanzania Craton is implying relatively larger effective elastic thickness compared to the northern part of the East African Rift System in the Afar region.

Centroid moment tensor inversions of offshore earthquakes using a three-dimensional velocity structure model: slip distributions on the plate boundary along the Nankai Trough

SUMMARYDue to complex 3-D heterogeneous structures, conventional 1-D analysis techniques using onshore seismograms can yield incorrect estimation of earthquake source parameters, especially dip angles and centroid depths of offshore earthquakes. Combining long-term onshore seismic observations and numerical simulations of seismic wave propagation in a 3-D model, we conducted centroid moment tensor (CMT) inversions of earthquakes along the Nankai Trough between April 2004 and August 2019 to evaluate decade-scale seismicity. Green's functions for CMT inversions of earthquakes with moment magnitudes of 4.3–6.5 were evaluated using finite-difference method simulations of seismic wave propagation in the regional 3-D velocity structure model. Significant differences of focal mechanisms and centroid depths between previous 1-D and our 3-D catalogues were found in the solutions of offshore earthquakes. By introducing the 3-D structures of the low-velocity accretionary prism and the Philippine Sea Plate, dip angles and centroid depths for offshore earthquakes were well-constrained. Teleseismic CMT also provides robust solutions, but our regional 3-D CMT could provide better constraints of dip angles. Our 3-D CMT catalogue and published slow earthquake catalogues depicted spatial distributions of slip behaviours on the plate boundary along the Nankai Trough. The regular and slow interplate earthquakes were separately distributed, with these distributions reflecting the heterogeneous distribution of effective strengths along the Nankai Trough plate boundary. By comparing the spatial distribution of seismic slip on the plate boundary with the slip-deficit rate distribution, regions with strong coupling were clearly identified.

Parameter estimation with a spinning multimode waveform model

Gravitational waves from compact binary coalescence sources can be decomposed into spherical-harmonic multipoles, the dominant being the quadrupole ($\ell=2, m=\pm2$) modes. The contribution of sub-dominant modes towards total signal power increases with increasing binary mass ratio and source inclination to the detector. It is well-known that in these cases neglecting higher modes could lead to measurement biases, but these have not yet been quantified with a higher-mode model that includes spin effects. In this study, we use the multi-mode aligned-spin phenomenological waveform model IMRPhenomHM to investigate the effects of including multi-mode content in estimating source parameters and contrast the results with using a quadrupole-only model (IMRPhenomD). We use as sources IMRPhenomHM and hybrid EOB-NR waveforms over a range of mass-ratio and inclination combinations, and recover the parameters with IMRPhenomHM and IMRPhenomD. These allow us to quantify the accuracy of parameter measurements using a multi-mode model, the biases incurred when using a quadrupole-only model to recover full (multi-mode) signals, and the systematic errors in the IMRPhenomHM model. We see that the parameters recovered by multi-mode templates are more precise for all non-zero inclinations as compared to quadrupole templates. For multi-mode injections, IMRPhenomD recovers biased parameters for non-zero inclinations with lower likelihood while IMRPhenomHM recovered parameters are accurate for most cases, and if a bias exists, it can be explained as a combined effect of observational priors and (in the case of hybrid-NR signals) waveform inaccuracies. For cases where IMRPhenomHM recovers biased parameters, the bias is always smaller than the corresponding IMRPhenomD recovery, and we conclude that IMRPhenomHM will be sufficiently accurate to allow unbiased measurements for most GW observations.

Bayesian Inversion of Wrapped Satellite Interferometric Phase to Estimate Fault and Volcano Surface Ground Deformation Models

AbstractBayesian inference and an improved downsampling method is used to determine earthquake and volcano source parameters using a popular geodetic observation method, satellite radar interferometry. The main novelty of the proposed approach is that the interferometric wrapped phase can be directly inverted, circumventing the ill‐posed phase unwrapping processing step. Phase unwrapping errors severely affect the estimation of earthquake and volcano source parameters using interferometric observations. Therefore, it is desirable to avoid phase unwrapping completely. To overcome the need for phase unwrapping, we propose a downsampling algorithm and a method to estimate the covariance function of the wrapped phase and establish an appropriate misfit function between the observed and simulated wrapped phase. Uncertainties in source parameters are assessed with a Bayesian approach, and finally, the robustness of the inversion methodology is tested in multiple simulations including variable decorrelation and atmospheric noise simulations. The method is shown to be robust in challenging noise scenarios. It features an improvement in performance with the Bayesian approach, compared to similar previous methods, avoiding any influence of seed starting models and escaping local minima. The impact of a small percentage of incorrectly unwrapped phase observations in current state‐of‐the‐art methods is shown to strongly affect the estimation process. We conclude that in the cases where phase unwrapping is difficult or even impossible, the proposed inversion methodology with wrapped phase will provide an alternative approach to assess earthquake and volcano source model parameters.

Too-Late Warnings by Estimating Mw: Earthquake Early Warning in the Near-Fault Region

ABSTRACTEarthquake early warning (EEW) systems aim to provide advance warnings of impending strong ground shaking. Many EEW systems are based on a strategy in which precise and rapid estimates of source parameters, such as hypocentral location and moment magnitude (Mw), are used in a ground-motion prediction equation (GMPE) to predict the strength of ground motion. For large earthquakes with long rupture duration, the process is repeated, and the prediction is updated in accordance with the growth of Mw during the ongoing rupture. However, in some regions near the causative fault this approach leads to late warnings, because strong ground motions often occur during earthquake ruptures before Mw can be confirmed. Mw increases monotonically with elapsed time and reaches its maximum at the end of rupture, and ground motion predicted by a GMPE similarly reaches its maximum at the end of rupture, but actual generation of strong motion is earlier than the end of rupture. A time gap between maximum Mw and strong-motion generation is the first factor contributing to late warnings. Because this time gap exists at any point of time during the rupture, a late warning is inherently caused even when the growth of Mw can be monitored in real time. In the near-fault region, a weak subevent can be the main contributor to strong ground motion at a site if the distance from the subevent to the site is small. A contribution from a weaker but nearby subevent early in the rupture is the second factor contributing to late warnings. Thus, an EEW strategy based on rapid estimation of Mw is not suitable for near-fault regions where strong shaking is usually recorded. Real-time monitoring of ground motion provides direct information for real-time prediction for these near-fault locations.