Estimation Of Source Parameters Research Articles

Analysis of the similar epicenter earthquakes on 22 January 2013 and 01 June 2013, Central Gulf of Suez, Egypt

On 22 January 2013 an earthquake with local magnitude ML 4.1 occurred in the central part of the Gulf of Suez. Six months later on 1 June 2013 another earthquake with local magnitude ML 5.1 took place at the same epicenter and different depths. These two perceptible events were recorded and localized by the Egyptian National Seismological Network (ENSN) and additional networks in the region.The purpose of this study is to determine focal mechanisms and source parameters of both earthquakes to analyze their tectonic relation. We determine the focal mechanisms by applying moment tensor inversion and first motion analysis of P- and S-waves. Both sources reveal oblique focal mechanisms with normal faulting and strike-slip components on differently oriented faults. The source mechanism of the larger event on 1 June in combination with the location of aftershock sequence indicates a left-lateral slip on N-S striking fault structure in 21 km depth that is in conformity with the NE-SW extensional Shmin (orientation of minimum horizontal compressional stress) and the local fault pattern. On the other hand, the smaller earthquake on 22 January with a shallower hypocenter in 16 km depth seems to have happened on a NE-SW striking fault plane sub-parallel to Shmin. Thus, here an energy release on a transfer fault connecting dominant rift-parallel structures might have resulted in a stress transfer, triggering the later ML 5.1 earthquake.Following Brune’s model and using displacement spectra, we calculate the dynamic source parameters for the two events. The estimated source parameters for the 22 January 2013 and 1 June 2013 earthquakes are fault length (470 and 830 m), stress drop (1.40 and 2.13 MPa), and seismic moment (5.47E+21 and 6.30E+22 dyn cm) corresponding to moment magnitudes of MW 3.8 and 4.6, respectively.

Assessment of teleseismically-determined source parameters for the April 25, 2015 MW 7.9 Gorkha, Nepal earthquake and the May 12, 2015 MW 7.2 aftershock

On April 25, 2015 a major (MW 7.9) thrust earthquake ruptured the deeper portion of the seismogenic plate boundary beneath Nepal along which India is underthrusting Eurasia. An MW 7.2 aftershock on May 12, 2015 extended the eastern, down-dip edge of the rupture. These destructive events caused about 9000 fatalities and 23,000 injuries. The overall rupture zone is about 170km long and 40–80km wide. This region of the plate boundary previously experienced a large earthquake in 1833, and in 1934 a larger MS 8.0 event located to the east ruptured all the way to the surface. The Main Himalayan Thrust (MHT) on which slip occurred in 2015 has a very low dip angle of ~6°, and the depth of the mainshock slip distribution is very shallow, extending from ~7 to ~18km. The shallow dip and depth present challenges for resolving faulting characteristics using teleseismic data. We analyze global teleseismic signals for the mainshock and aftershock to estimate source parameters, evaluating the stability of various procedures used for remotely characterizing kinematics of such shallow faulting. Back-projection and finite-fault slip inversion are used to assess the spatio-temporal rupture history and evidence for frequency-dependent radiation along dip. Slip zone width constraints from near-field geodetic observations are imposed on the preferred models to overcome some limitations of purely teleseismic methods. Radiated energy, stress drop and moment rate functions are determined for both events.

Volcano deformation source parameters estimated from InSAR: Sensitivities to uncertainties in seismic tomography

AbstractThe eruption cycle of a volcano is controlled in part by the upward migration of magma. The characteristics of the magma flux produce a deformation signature at the Earth's surface. Inverse analyses use geodetic data to estimate strategic controlling parameters that describe the position and pressurization of a magma chamber at depth. The specific distribution of material properties controls how observed surface deformation translates to source parameter estimates. Seismic tomography models describe the spatial distributions of material properties that are necessary for accurate models of volcano deformation. This study investigates how uncertainties in seismic tomography models propagate into variations in the estimates of volcano deformation source parameters inverted from geodetic data. We conduct finite element model‐based nonlinear inverse analyses of interferometric synthetic aperture radar (InSAR) data for Okmok volcano, Alaska, as an example. We then analyze the estimated parameters and their uncertainties to characterize the magma chamber. Analyses are performed separately for models simulating a pressurized chamber embedded in a homogeneous domain as well as for a domain having a heterogeneous distribution of material properties according to seismic tomography. The estimated depth of the source is sensitive to the distribution of material properties. The estimated depths for the homogeneous and heterogeneous domains are 2666 ± 42 and 3527 ± 56 m below mean sea level, respectively (99% confidence). A Monte Carlo analysis indicates that uncertainties of the seismic tomography cannot account for this discrepancy at the 99% confidence level. Accounting for the spatial distribution of elastic properties according to seismic tomography significantly improves the fit of the deformation model predictions and significantly influences estimates for parameters that describe the location of a pressurized magma chamber.

Solving probabilistic inverse problems rapidly with prior samples

Owing to the increasing availability of computational resources, in recent years the probabilistic solution of non-linear, geophysical inverse problems by means of sampling methods has become increasingly feasible. Nevertheless, we still face situations in which a Monte Carlo approach is not practical. This is particularly true in cases where the evaluation of the forward problem is computationally intensive or where inversions have to be carried out repeatedly or in a timely manner, as in natural hazards monitoring tasks such as earthquake early warning. Here,we present an alternative to Monte Carlo sampling, inwhich inferences are entirely based on a set of prior samples-that is, samples that have been obtained independent of a particular observed datum. This has the advantage that the computationally expensive sampling stage becomes separated from the inversion stage, and the set of prior samples-once obtained-can be reused for repeated evaluations of the inverse mapping without additional computational effort. This property is useful if the problem is such that repeated inversions of independent data have to be carried out.We formulate the inverse problem in a Bayesian framework and present a practical way to make posterior inferences based on a set of prior samples. We compare the prior sampling based approach to a Markov Chain Monte Carlo approach that samples from the posterior probability distribution. We show results for both a toy example, and a realistic seismological source parameter estimation problem. We find that the posterior uncertainty estimates obtained based on prior sampling can be considered conservative estimates of the uncertainties obtained by directly sampling from the posterior distribution. Published by Oxford University Press on behalf of The Royal Astronomical Society.

The Virtual Seismologist in SeisComP3: A New Implementation Strategy for Earthquake Early Warning Algorithms

The feasibility of earthquake early warning (EEW) is now widely recognized. However, EEW systems that are in operation or under evaluation worldwide have significant variations and are usually operated independently of routine earthquake monitoring. We introduce a software that allows testing and evaluation of a well‐known EEW algorithm directly within a widely used earthquake monitoring software platform. In the long term, we envision this approach can lead to (1) an easier transition from prototype to production type EEW implementations, (2) a natural and seamless evolution from very fast EEW source parameter estimates with typically large uncertainties to more delayed but more precise estimates using more traditional analysis methods, and (3) the capability of seismic networks to evaluate the readiness of their network for EEW, and to implement EEW, without having to invest in and maintain separate, independent software systems. Using the Virtual Seismologist (VS), a popular EEW algorithm that has been tested in real time in California since 2008, we demonstrate how our approach can be realized within the widely used monitoring platform SeisComP3. Because this software suite is already in production at many seismic networks worldwide, we have been able to test the new VS implementation across a wide variety of tectonic settings and network infrastructures. Using mainly real‐time performance, we analyze over 3200 events with magnitudes between 2.0 and 6.8 and show that, for shallow crustal seismicity, 68% of the first VS magnitude estimates are within ±0.5 magnitude units of the final reported magnitude. We further demonstrate the very significant effect of data communication strategies on final alert times. Using a Monte Carlo simulation approach, we then model the best possible alert times for optimally configured EEW systems and show that, for events within the dense parts of each of the seven test networks, effective warnings could be issued for magnitudes as small as M 5.0.

The intraplate Mw 7 Machaze earthquake in Mozambique: Improved point source model, stress drop, and geodynamic implications

The February 22nd 2006 Mw = 7 Machaze earthquake is one of the largest, if not the largest, earthquakes reported since 1900 within Continental Africa. This large continental intraplate event has important implications to our understanding of tectonics and strong ground motion prediction locally and in the global context. Thus, accurate estimates of source parameters of this earthquake are important. In this study, we inverted the complete azimuthally distributed high frequency (0.05–2 Hz) P waveform dataset available for a best-fitting point source model and obtained stress drop estimates assuming different theoretical rupture models from spectral fitting. Our best-fitting point source model confirms steep normal faulting, has strike = 173° (309°), dip = 73° (23°), rake = −72° (−132°), and shows a 12%–4% improvement in waveform fit compared to previous models, which translates into an error minimization. We attribute this improvement to higher order reverberations near the source region that we took in to account and the excellent azimuthal coverage of the dataset. Preferred stress drop estimates assuming a rupture velocity = 0.9 x shear wave velocity (Vs) are between 11 and 15 MPa though, even higher stress drop estimates are possible for rupture velocities lower than 0.9Vs. The estimated stress drop is significantly higher than the global stress drop average of intraplate earthquakes, but is consistent with stress drop estimated for some intra-continental earthquakes elsewhere. The detection of a new active structure that appears to terminate in Machaze, its step-like geometry, and lithospheric strength all favors a hypothesis of stress concentration in the source region, which is likely the cause of this event and the higher than average stress drop.

Self-constrained inversion of microgravity data along a segment of the Irpinia fault

A microgravity survey was completed to precisely locate and better characterize the near-surface geometry of a recent fault with small throw in a mountainous area in the Southern Apennines (Italy). The site is on a segment of the Irpinia fault, which is the source of the M6.9 1980 earthquake. This fault cuts a few meter of Mesozoic carbonate bedrock and its younger, mostly Holocene continental deposits cover. The amplitude of the complete Bouguer anomaly along two profiles across the fault is about 50μGal. The data were analyzed and interpreted according to a self-constrained strategy, where some rapid estimation of source parameters was later used as constraint for the inversion. The fault has been clearly identified and localized in its horizontal position and depth. Interesting features in the overburden have been identified and their interpretation has allowed us to estimate the fault slip-rate, which is consistent with independent geological estimates.

Rapid earthquake focal mechanism inversion using high-rate GPS velometers in sparse network

In this study, we demonstrate an approach for inverting earthquake source parameters based on high-rate global positioning system (GPS) velocity seismograms. The velocity records obtained from single-station GPS velocity solutions with broadcast ephemeris are used directly for earthquake source parameter inversion using the Cut and Paste method, without requiring conversion of the velocity records into displacement records. Taking the El Mayor-Cucapah earthquake as an example, GPS velocity records from 10 stations with reasonable azimuthal coverage provide earthquake source parameters very close to those from the Global centroid moment tensor (Global CMT) solution. In sparse network tests, robust source parameters with acceptable bias can be achieved with as few as three stations. When the number of stations is reduced to two, the bias in rake angle becomes appreciable, but the magnitude and strike estimations are still robust. The results of this study demonstrate that rapid and reliable estimation of earthquake source parameters can be obtained from GPS velocity data. These parameters could be used for early earthquake warning and shake map construction, because such GPS velocity records can be obtained in real time.

Acoustic source inversion to estimate volume flux from volcanic explosions

AbstractWe present an acoustic waveform inversion technique for infrasound data to estimate volume fluxes from volcanic eruptions. Previous inversion techniques have been limited by the use of a 1‐D Green's function in a free space or half space, which depends only on the source‐receiver distance and neglects volcanic topography. Our method exploits full 3‐D Green's functions computed by a numerical method that takes into account realistic topographic scattering. We apply this method to vulcanian eruptions at Sakurajima Volcano, Japan. Our inversion results produce excellent waveform fits to field observations and demonstrate that full 3‐D Green's functions are necessary for accurate volume flux inversion. Conventional inversions without consideration of topographic propagation effects may lead to large errors in the source parameter estimate. The presented inversion technique will substantially improve the accuracy of eruption source parameter estimation (cf. mass eruption rate) during volcanic eruptions and provide critical constraints for volcanic eruption dynamics and ash dispersal forecasting for aviation safety. Application of this approach to chemical and nuclear explosions will also provide valuable source information (e.g., the amount of energy released) previously unavailable.

Attenuation and Apparent Source Characteristics in the Northern Indian Oceanic Crust Surrounding Sri Lanka

A data analysis of 171 broadband vertical‐component records of 62 shallow crustal distant events in the northern Indian Ocean region was undertaken to investigate the far‐source geometric attenuation rate, high‐frequency cutoff filter parameter (kappa), and apparent source characteristics. Event magnitude varied from 4.0 to 5.9 in the short‐period body‐wave magnitude ( m b) scale, and hypocentral distance ranged between 2.3° (260 km) and 14.1° (1578 km) for the dataset. The far‐source geometric attenuation rate was estimated by fitting data to a predefined attenuation equation at a frequency range of 0.5–8.5 Hz, using the multiple linear regression method. A secondary regression in the frequency domain on constants resulting from the main (first) regression was performed to find kappa and the second hinge point of the trilinear geometric attenuation function. Source characteristics (stress drop, corner frequency, and moment magnitude) of selected events were determined using the Brune (1970, 1971) model. The average far‐source geometric attenuation rate was determined to be R −0.5 ( R is hypocentral distance) for the selected frequency range, but at low frequencies (below about 2 Hz) slightly lower rates than the average were observed. Kappa was found to be 0.041±0.009 s. The second hinge point of the geometric attenuation function was estimated to be 120±30 km, and the complete form of the function, after considering compliancy with actual records, was collated as ![Graphic][1] Average static stress drops were found to be 9.5 and 16.0 MPa for the m b 4–5 and 5–6 magnitude bands, respectively. Corner frequencies approximately fell within 1.0–7.0 Hz for the dataset. Derived attenuation parameters were also validated using a ground‐motion comparison between recorded and stochastically simulated events. Online Material: Tables of regression parameters, estimated source parameters, and stochastic simulation parameters, and a figure comparing the ground motion for simulated and recorded events. [1]: /embed/inline-graphic-1.gif

Application of a Threshold-Based Earthquake Early Warning Method to the Mw 6.6 Lushan Earthquake, Sichuan, China

Mitigation of earthquake damages remains an open task, despite the fact that many solutions have been proposed in the recent past. In this framework, the so‐called earthquake early warning systems (EEWS) try to exploit the short time interval between the earthquake occurrence and the arrival of the destructive wavetrain to warn the population or to perform some automatic actions that can reduce damages induced by the ground shaking. A rapid analysis of real‐time data from seismic stations deployed in the source region is the key element in such system. During the last three decades, the EEWS is increasingly used to reduce exposure of populations to seismic risk, and several countries around the world have already developed EEWS, or are on the verge of doing so. Japan, Taiwan, Mexico, and California, for example, already have operational EEWSs (Wu and Teng, 2002; Horiuchi et al. , 2005; Wu and Zhao, 2006; Hoshiba et al. , 2008; Espinosa‐Aranda et al. , 2009). In particular, the EEWS developed by the Japan Meteorological Agency began to send early‐warning information to general public since 2007. EEWSs are also under development and testing in other regions of the world, including Italy, Turkey, Romania, and China (Allen and Kanamori, 2003; Bose et al. , 2007; Alcik et al. , 2009; Allen, Brown, et al. , 2009; Allen, Gasparini, et al. , 2009; Bose et al. , 2009; Zollo et al. , 2010; Peng et al. , 2011; Satriano et al. , 2011; Kuyuk et al. , 2014). Most EEWS are designed as either regional (or network‐based) or onsite (or station‐based) systems. Deployment of the EEWS essentially depends on network geometry and source‐to‐site distance. In a regional EEWS, the early portion of recorded signals is used to rapidly estimate source parameters (event location and magnitude) and to …

Source study of three moderate size recent earthquakes in the Guerrero seismic gap

We study three recent earthquakes of different types in the Guerrero seismic gap zone with M ≥ 6.5: the 15 July 1996 Guerrero near-coast interplate earthquake (Mw = 6.6), the 18 April 2002 Guerrero near-trench interplate earthquake (Mw = 6.7), and the 11 December 2011 Guerrero normal-faulting inslab earthquake (Mw = 6.5). We compute the slip distributions, estimate source parameters, and model strong ground motions with the finite-fault stochastic method. We use different methods to estimate source parameters in order to observe differences in stress drop and radiated seismic energy among these events. The similarity in seismic magnitude gives us the opportunity to compare our results for the three different types of earthquake and interpret them in terms of the tectonic environments and seismic hazard. We analyze the peak ground accelerations and their relation with the stress drop. We simulated ground motions with the stochastic method. The model parameters are validated against recordings and a stress drop of 3, 15, and 70 MPa is estimated for the near-trench interplate, near-coast interplate, and normal-faulting inslab events, respectively. The near-trench interplate event has the lowest radiated seismic energy and the lowest rupture velocity. This is reflected in the energy to moment ratio of 2.17 × 10−6, 4.52 × 10−6, and 3.96 × 10−6 for the near-trench interplate, near-coast interplate, and normal-faulting inslab events, respectively. We define asperities using two different criteria: (1) based on average displacement and (2) maximum displacement. The asperity area for the near-coast and near-trench interplate events represents about 23 and 24–25 % of the total rupture area, which in the case of the normal-faulting inslab event, it is only 19 and 23 % based on average and maximum displacement, respectively.

Single channel source separation and parameter estimation of multi-component PRBCPM-SFM signal based on generalized period

This paper proposes an approach of single channel source separation and parameter estimation of multi-component PRBCPM-SFM (pseudo-random binary code phase modulated sinusoidal frequency modulation) signal. By transforming all components to SFM signals through square calculation, we may then apply singular value decomposition to determine the generalized period and the modulation frequency of the SFM signal. The modulation index and carrier frequency are determined by searching for discrete points and optimizing calculations. The initial phase can be determined by calculating the inner product. Finally, given that the pseudo-random binary code is a real signal, the PN (Pseudo-noise) sequence and the amplitude can be estimated. Our proposed method can estimate the SNR by using the method of subspace-based decomposition, and the estimated SNR can be used to adaptively stop separation. Experimental results demonstrate the algorithm's performance.

Characterization of Source Parameters and Some Empirical Relations between Them for Kachchh Region, Gujarat, India: Implication of January 26, 2001 Bhuj Earthquake and Its Aftershock Sequence

Study of source parameters of small to moderate and large earthquakes is important to understand the differences and similarities between dynamic ruptures of different earthquakes and clarifying the scaling relations. In the present study, we have characterized source parameters and presented new and revised empirical relationships between various source parameters for Kachchh region of Gujarat, India to facilitate to draw first-order conclusions regarding the trends in the region. We have studied total 202 aftershocks of shallow-focus (hypo central depth less than 40 km) and moderate magnitude recorded over the Kachchh region during January 2001 to December 2012 by different seismological observatories of India Meteorological Department. We have adopted the spectral technique for source parameter estimation, where S-wave displacement spectra are considered and applied Fast Fourier Transform (FFT) to compute displacement spectra. We have followed the Brune’s source model for our estimation and the estimated values of source parameters show close approximation to the global values. While derived empirical relations between different source parameters, they demonstrate direct or inverse proportion to linear or power scale. Interrelation between seismic moment, rupture parameters, corner frequency and radiated seismic energy can be summarized as , , and ER μ M0 and ER μ Mw for our analysis. Stress drop distribution over the Kachchh region is very scattered and due to its peculiar behavior, it is difficult to derive its empirical relation with other source parameters. Sufficient accuracy on measuring source parameters like corner frequency stress drop, rupture dimensions, radiated seismic energy etc. helps to understand earthquake processes in the region. This is the first ever attempt to establish empirical relation between different source parameters for Kachchh region for longer aftershock sequence and they are useful to assess future earthquake potential over the region.

Advances in earthquake and tsunami sciences and disaster risk reduction since the 2004 Indian ocean tsunami

The December 2004 Indian Ocean tsunami was the worst tsunami disaster in the world’s history with more than 200,000 casualties. This disaster was attributed to giant size (magnitude M ~ 9, source length >1000 km) of the earthquake, lacks of expectation of such an earthquake, tsunami warning system, knowledge and preparedness for tsunamis in the Indian Ocean countries. In the last ten years, seismology and tsunami sciences as well as tsunami disaster risk reduction have significantly developed. Progress in seismology includes implementation of earthquake early warning, real-time estimation of earthquake source parameters and tsunami potential, paleoseismological studies on past earthquakes and tsunamis, studies of probable maximum size, recurrence variability, and long-term forecast of large earthquakes in subduction zones. Progress in tsunami science includes accurate modeling of tsunami source such as contribution of horizontal components or “tsunami earthquakes”, development of new types of offshore and deep ocean tsunami observation systems such as GPS buoys or bottom pressure gauges, deployments of DART gauges in the Pacific and other oceans, improvements in tsunami propagation modeling, and real-time inversion or data assimilation for the tsunami warning. These developments have been utilized for tsunami disaster reduction in the forms of tsunami early warning systems, tsunami hazard maps, and probabilistic tsunami hazard assessments. Some of the above scientific developments helped to reveal the source characteristics of the 2011 Tohoku earthquake, which caused devastating tsunami damage in Japan and Fukushima Dai-ichi Nuclear Power Station accident. Toward tsunami disaster risk reduction, interdisciplinary and trans-disciplinary approaches are needed for scientists with other stakeholders.

Improving the local wavenumber method by automatic DEXP transformation

In this paper we present a new method for source parameter estimation, based on the local wavenumber function. We make use of the stable properties of the Depth from EXtreme Points (DEXP) method, in which the depth to the source is determined at the extreme points of the field scaled with a power-law of the altitude. Thus the method results particularly suited to deal with local wavenumber of high-order, as it is able to overcome its known instability caused by the use of high-order derivatives. The DEXP transformation enjoys a relevant feature when applied to the local wavenumber function: the scaling-law is in fact independent of the structural index. So, differently from the DEXP transformation applied directly to potential fields, the Local Wavenumber DEXP transformation is fully automatic and may be implemented as a very fast imaging method, mapping every kind of source at the correct depth. Also the simultaneous presence of sources with different homogeneity degree can be easily and correctly treated. The method was applied to synthetic and real examples from Bulgaria and Italy and the results agree well with known information about the causative sources.

New Tsunami Forecast Tools for the French Polynesia Tsunami Warning System

This paper presents the tsunami warning tools, which are used for the estimation of the seismic source parameters. These tools are grouped under a method called Preliminary Determination of Focal Mechanism_2 (PDFM2), that has been developed at the French Polynesia Warning Center, in the framework of the \(SEISCOMP3\) system, as a plug-in concept. The first tool determines the seismic moment and the focal geometry (strike, dip, and slip), and the second tool identifies the ”tsunami earthquakes” (earthquakes that cause much bigger tsunamis than their magnitude would imply). In a tsunami warning operation, initial assessment of the tsunami potential is based on location and magnitude. The usual quick magnitude methods which use \(P\) waves, work fine for smaller earthquakes. For major earthquakes these methods drastically underestimate the magnitude and its tsunami potential because the radiated energy shifts to the longer period waves. Since French Polynesia is located far away from the subduction zones of the Pacific rim, the tsunami threat is not imminent, and this luxury of time allows to use the long period surface wave data to determine the true size of a major earthquake. The source inversion method presented in this paper uses a combination of surface waves amplitude spectra and P wave first motions. The advantage of using long period surface data is that there is a much more accurate determination of earthquake size, and the advantage of using P wave first motion is to have a better constrain of the focal geometry than using the surface waves alone. The \(PDFM2\) method routinely gives stable results at \(T_0 + 45\) minutes, with \(T_0\) being the origin time of an earthquake. Our results are then compared to the Global Centroid Moment Tensor catalog for validating both the seismic moment and the source geometry. The second tool discussed in this paper is the slowness parameter \(\theta,\) and is the energy-to-moment ratio. It has been used to identify tsunami earthquakes, which are characterized by having unusual slow rupture velocity and release seismic energy that has been shifted to longer periods and, therefore, have low \(\theta\) values. The slow rupture velocity would indicate weaker material and bigger uplift and, thus, bigger tsunami potential. The use of the slowness parameter \(\theta\) is an efficient tool for monitoring the near real-time identification of tsunami earthquakes.

Hybrid algorithm of minimum relative entropy-particle swarm optimization with adjustment parameters for gas source term identification in atmosphere

In order to identify the source term of gas emission in atmosphere, an improved hybrid algorithm combined with the minimum relative entropy (MRE) and particle swarm optimization (PSO) method was presented. Not only are the estimated source parameters obtained, but also the confidence intervals at some probability levels. If only the source strength was required to be determined, the problem can be viewed as a linear inverse problem directly, which can be solved by original MRE method successfully. When both source strength and location are unknown, the common gas dispersion model should be transformed to be a linear system. Although the transformed linear model has some differences from that in original MRE method, satisfied estimation results were still obtained by adding iteratively adaptive adjustment parameters in the MRE-PSO method. The dependence of the MRE-PSO method on prior information such as lower and upper bound, prior expected values and noises were also discussed. The results showed that the confidence intervals and estimated parameters are influenced little by the prior bounds and expected values, but the errors affect the estimation results greatly. The simulation and experiment verification results showed that the MRE-PSO method is able to identify the source parameters with satisfied results. Finally, the error model was probed and then it was added in the MRE-PSO method. The addition of error model improves the performance of the identification method. Therefore, the MRE-PSO method with adjustment parameters proposed in this paper is a potential good method to resolve inverse problem in atmosphere environment.

Source study of the Jan Mayen transform fault strike-slip earthquakes

Seismic source parameters of oceanic transform zone earthquakes have been relatively poorly studied. Previous studies showed that this type of earthquakes has unique characteristics such as not only the relatively common occurrence of slow events with weak seismic radiation at high frequencies but also the occurrence of some events that have high apparent stress indicating strong high frequency radiation. We studied 5 strike-slip earthquakes in the Jan Mayen fracture zone with magnitudes in the range of 5.9<Mw<6.7. We determined finite-fault slip distributions with the iterative deconvolution method from teleseismic data. The slip models were characterized by determining source parameters on the asperities and background areas. We found that the areas of the asperities represent about 23–28% of the total rupture area with two different criteria based on average slip and maximum displacement. Sensitivity tests were carried out to estimate the variability of slip patterns and source parameters. We observed robust solutions and reliable source parameter estimates from the models. We also determined the radiated seismic energy and apparent stress in order to identify possible slow events. Our results suggest that the analyzed events in Jan Mayen have a regular nature in terms of apparent stress, seismic energy and centroid time delay compared to other oceanic transform fault earthquakes.

Source Parameters of the 2001 Mw 7.7 Bhuj Earthquake, Gujarat, India, Aftershock Sequence

Abstract We present the estimated source parameters from SH-wave spectral modeling of selected 463 aftershocks (2002-06) of the 26 January 2001 Bhuj earthquake, the well-recorded largest continental intraplate earthquake. The estimated seismic moment (Mo), corner frequency (fc), source radius (r) and stress drop (Δσ) for aftershocks of moment magnitude 1.7 to 5.6 range from 3.55×1011 to 2.84×1017 N-m, 1.3 to 11.83 Hz, 107 to 1515 m and 0.13 to 26.7 MPa, respectively, while the errors in fc and Δσ are found to be 1.1 Hz and 1.1 MPa, respectively. We also notice that the near surface attenuation factor (k) values vary from 0.02 to 0.03. Our estimates reveal that the stress drop values show more scatter (Mo0.5 to 1 is proportional to Δσ) toward the larger Mo values (≥1014.5 N-m), while they show a more systematic nature (Mo3 is proportional to Δσ) for smaller Mo values (&amp;lt;1014.5 N-m), which can be explained as a consequence of a nearly constant rupture radius for smaller aftershocks in the region. The large stress drops (= 10 MPa) associated with events on the north Wagad fault (at 15-30 km depth) and Gedi fault (at 3-15 km depth) can be attributed to the large stress developed at hypocentral depths as a result of high fluid pressure and the presence of mafic intrusive bodies beneath these two fault zones.