Comparison of magnitudes estimated by the Japan Meteorological Agency with moment magnitudes for intermediate and deep earthquakes

1996 ◽  
Vol 86 (3) ◽  
pp. 832-842 ◽  
Author(s):  
Akio Katsumata
Keyword(s):  
Velocity Structure ◽  
Epicentral Distance ◽  
Moment Tensor ◽  
Focal Depth ◽  
Moment Magnitude ◽  
Japan Meteorological Agency ◽  
Maximum Displacement ◽  
Centroid Moment Tensor ◽  
Attenuation Function ◽  
Shallow Earthquakes

Abstract The magnitude, MJMA, estimated by the Japan Meteorological Agency (JMA) is generally referred to in Japan for the regional seismicity in the area. MJMA is determined from maximum displacement amplitudes of the total seismic wave traces. For earthquakes shallower than 60 km, MJMA is determined by Tsuboi's formula, and for earthquakes deeper than 60 km, by Katsumata's formula. These relations were designed to give almost the same magnitude value as that of Gutenberg and Richter. We compared MJMA with moment magnitude, MW, which can be calculated from the centroid moment tensor (CMT) solutions. It was found that the average difference between MJMA and MW is not significant for shallow earthquakes in the magnitude range from 5 to 7, but it is significant at a low level for the earthquakes of deeper foci. The averaged difference reaches about 0.4 magnitude units for the focal depth of 600 km. We derived an attenuation function for the maximum displacement amplitude assuming the validity of the moment magnitude. This relation between epicentral distance and amplitude for shallow earthquakes is almost identical to the one calculated from Tsuboi's formula. It is suggested that the estimated attenuation function for deep-focus earthquakes reflects the specific Q and velocity structure that is peculiar to the subduction zone.

scholarly journals Source Parameter of Earthquakes in Talala, Gujarat (India): An Implication towards Seismotectonic

Proceedings ◽  
2019 ◽  
Vol 24 (1) ◽  
pp. 7
Author(s):  
Sandeep Kumar Aggarwal
Keyword(s):  
Epicentral Distance ◽  
Moment Tensor ◽  
Source Parameters ◽  
Focal Depth ◽  
B Value ◽  
Complete Sequence ◽  
P Value ◽  
Centroid Moment Tensor ◽  
North East ◽  
Lateral Plane

Talala is an excellent example of triggered neo-tectonic seismicity between two dams during a monsoon. An earthquake of Mmax 5.1 on 6 November 2007 at 21.16° N; 70.54° E, with a focal depth of 4.5 km and complete sequence, was first-time recorded on the latest broadband sensor. This found a dam/monsoon-induced earthquake preceded by 18 foreshocks of 2 ≤ Mw ≤ 4.8 within 9 h 11 minute, as well as smaller shocks that may not have been recorded because of sparse network coverage. After the deployment of local mobile observatories, aftershocks of Mw ≥ 1.0, which continued for months and subsided to background seismicity after four months, were recorded. The same kind of phenomena repeated, with Mmax 5.0 on 20 October 2011 at 21.06° N; 70.50° E, focal depth 5.5 km, which implies that the potential to generate dam/monsoon-induced seismicity took nearly four years again. These phenomena continued and the sequence was recorded by a network of 10 broadband seismographs (three in the Talala area and seven at an epicentral distance of 30 to 300 km). Centroid Moment Tensor (CMT) solutions and spectral source parameters of mainshock and aftershocks are evaluated to understand the seismotectonic of the region. The CMT depicts a major strike-slip motion along East North East-West South West with a left-lateral plane at 4.5 km depth. This indicates a sympathetic fault extension of the Son-Narmada fault. The source parameters of 400 shocks of Mw 1.0 to 5.1 found seismic moment 1011 to 1016.5 N-m, source radii 120–850 meter, and a stress drop of 0.003 to 25.43 Mpa. The b-value, p-value, fractal dimension, and slip on estimated different faults. The comparison between Talala and Koyna dam-induced source parameters tries to establish a comparison of seismicity from different parts of the world.

Application of Mwp to deep and teleseismic earthquakes

1999 ◽  
Vol 89 (5) ◽  
pp. 1345-1351 ◽  
Author(s):  
Seiji Tsuboi ◽  
Paul M. Whitmore ◽  
Thomas J. Sokolowski
Keyword(s):  
Moment Tensor ◽  
Earthquake Magnitude ◽  
Moment Magnitude ◽  
Centroid Moment Tensor ◽  
Shallow Earthquakes ◽  
Japanese Islands ◽  
Tsunami Warnings ◽  
Size Estimates ◽  
Good Agreement

Abstract The broadband moment magnitude Mwp (Tsuboi, et al., 1995) allows for the effective determination of earthquake magnitude by using broadband P waveforms. It was developed to determine moment magnitude of shallow earthquakes around the Japanese Islands for early tsunami warnings. Tsuboi et al. (1995) demonstrated that Mwp shows good agreement with the Mw from Harvard centroid moment tensor (CMT) solutions. In the present study, we show that Mwp is also applicable to deep earthquakes and earthquakes recorded at teleseismic distances. The Mwp proves to be useful for quick, accurate size estimates of earthquakes recorded at both regional and teleseismic distances occurring at any depth.

scholarly journals New Updated Classification of Shallow Earthquakes Based on Faulting Style

2020 ◽  
pp. 103-111
Author(s):  
Emad Abulrahman Mohammed Salih Al-Heety
Keyword(s):  
Return Period ◽  
Moment Tensor ◽  
Focal Depth ◽  
Strike Slip ◽  
Shallow Depth ◽  
Main Trend ◽  
Maximum Magnitude ◽  
Centroid Moment Tensor ◽  
Significant Information

Earthquakes occur on faults and create new faults. They also occur on  normal, reverse and strike-slip faults. The aim of this work is to suggest a new unified classification of Shallow depth earthquakes based on the faulting styles, and to characterize each class. The characterization criteria include the maximum magnitude, focal depth, b-constant value, return period and relations between magnitude, focal depth and dip of fault plane. Global Centroid Moment Tensor (GCMT) catalog is the source of the used data. This catalog covers the period from Jan.1976 to Dec. 2017. We selected only the shallow (depth less than 70kms) pure, normal, strike-slip and reverse earthquakes (magnitude ≥ 5) and excluded the oblique earthquakes. The majority of normal and strike-slip earthquakes occurred in the upper crust, while the reverse earthquakes occurred throughout the thickness of the crust. The main trend for the derived b-values for the three classes was: b normal fault>bstrike-slip fault>breverse fault.  The mean return period for the normal earthquake was longer than that of the strike-slip earthquakes, while the reverse earthquakes had the shortest period. The obtained results report the relationship between the magnitude and focal depth of the normal earthquakes. A negative significant correlation between the magnitude and dip class for the normal and reverse earthquakes is reported. Negative and positive correlation relations between the focal depth and dip class were recorded for normal and reverse earthquakes, respectively. The suggested classification of earthquakes provides significant information to understand seismicity, seismtectonics, and seismic hazard analysis.

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

2020 ◽  
Vol 222 (2) ◽  
pp. 1109-1125 ◽  
Author(s):  
Shunsuke Takemura ◽  
Ryo Okuwaki ◽  
Tatsuya Kubota ◽  
Katsuhiko Shiomi ◽  
Takeshi Kimura ◽  
...  
Keyword(s):  
Wave Propagation ◽  
Seismic Wave ◽  
Velocity Structure ◽  
Nankai Trough ◽  
Moment Tensor ◽  
Plate Boundary ◽  
Seismic Wave Propagation ◽  
Structure Model ◽  
Centroid Moment Tensor ◽  
Heterogeneous Distribution

SUMMARY Due 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.

scholarly journals Accounting for theory errors with empirical Bayesian noise models in nonlinear centroid moment tensor estimation

2021 ◽  
Author(s):  
H Vasyura-Bathke ◽  
J Dettmer ◽  
R Dutta ◽  
P M Mai ◽  
S Jónsson
Keyword(s):  
Parameter Estimation ◽  
Uncertainty Quantification ◽  
Measurement Errors ◽  
Velocity Structure ◽  
Moment Tensor ◽  
Velocity Model ◽  
Model Uncertainties ◽  
Centroid Moment Tensor ◽  
Uncertainty Estimates ◽  
Noise Models

Summary Centroid moment-tensor (CMT) parameters can be estimated from seismic waveforms. Since these data indirectly observe the deformation process, CMTs are inferred as solutions to inverse problems which are generally under-determined and require significant assumptions, including assumptions about data noise. Broadly speaking, we consider noise to include both theory and measurement errors, where theory errors are due to assumptions in the inverse problem and measurement errors are caused by the measurement process. While data errors are routinely included in parameter estimation for full CMTs, less attention has been paid to theory errors related to velocity-model uncertainties and how these affect the resulting moment-tensor (MT) uncertainties. Therefore, rigorous uncertainty quantification for CMTs may require theory-error estimation which becomes a problem of specifying noise models. Various noise models have been proposed, and these rely on several assumptions. All approaches quantify theory errors by estimating the covariance matrix of data residuals. However, this estimation can be based on explicit modelling, empirical estimation, and/or ignore or include covariances. We quantitatively compare several approaches by presenting parameter and uncertainty estimates in non-linear full CMT estimation for several simulated data sets and regional field data of the Ml 4.4, 13 June 2015 Fox Creek, Canada, event. While our main focus is at regional distances, the tested approaches are general and implemented for arbitrary source model choice. These include known or unknown centroid locations, full MTs, deviatoric MTs, and double-couple MTs. We demonstrate that velocity-model uncertainties can profoundly affect parameter estimation and that their inclusion leads to more realistic parameter uncertainty quantification. However, not all approaches perform equally well. Including theory errors by estimating non-stationary (non-Toeplitz) error covariance matrices via iterative schemes during Monte Carlo sampling performs best and is computationally most efficient. In general, including velocity-model uncertainties is most important in cases where velocity structure is poorly known.

scholarly journals Shallow soil effects for contrasting PGAs at nearby strong-motion stations during the 2017, Mj 5.2, southern Akita Prefecture earthquake

2021 ◽  
Vol 62 ◽  
pp. 34-46
Author(s):  
Yadab P. Dhakal ◽  
Wataru Suzuki ◽  
Takeshi Kimura ◽  
Takashi Kunugi ◽  
Shin Aoi
Keyword(s):  
Ground Motion ◽  
Epicentral Distance ◽  
Focal Depth ◽  
Strong Motion ◽  
Disaster Mitigation ◽  
Japan Meteorological Agency ◽  
Velocity Models ◽  
Wide Range ◽  
Akita Prefecture ◽  
Neighboring Sites

On September 8, 2017, an earthquake of Mj 5.2 occurred with the epicenter in southern Akita Prefecture, Japan, at 22:23 local time. According to the Japan Meteorological Agency (JMA), the focal depth was 9 km. Many strong-motion stations of K-NET and KiK-net recorded ground motions from the earthquake. The maximum horizontal vector peak ground acceleration (PGA) of approximately 136 cm/s2 was recorded at one of the KiK-net stations at an epicentral distance of about 8 km. However, despite being 37 km and 53 km far from the epicenter, two stations recorded PGAs of approximately 126 and 113 cm/s2, respectively, similar to that near the epicenter. Even though these PGAs are not rare, we found that the PGAs at the two sites strongly deviated from the median values suggested by a ground motion prediction equation (GMPE), while the nearby sites generally followed the GMPE. Available velocity models showed that shallow shear wave velocities, especially in the top 5 m, were lower (i.e., the soils were softer) at the two sites compared to those at their nearest neighboring sites. We compared the ratios of the PGAs and peak ground velocities (PGVs) at the two sites with respect to their neighboring sites for many earthquakes covering a wide range of magnitudes and azimuths. We found that the PGAs and PGVs at the two sites were systematically larger than those at the adjacent sites. Linear theoretical site amplifications using the available soil models gave peak frequencies around 6-8 Hz at the larger PGA sites. Bandpass-filtered records showed significantly larger PGAs around these frequencies at the larger PGA sites. The above results showed that local site condition is one of the major contributing factors to induce large PGAs. Furthermore, softer sites experience more substantial nonlinear site amplification than the stiffer sites when input motions exceed some threshold PGAs. This latter effect means that the softer sites can produce a variety of ground motion spectra. Nevertheless, the degree of damage to built structures depends on several factors, including the design and quality of construction. We expect that this study contributes to developing improved microzonation maps for earthquake disaster mitigation.

scholarly journals The Reliance of the Earthquake B-Value on Depth and Focal Mechanism

2021 ◽  
Vol 54 (1D) ◽  
pp. 1-10
Author(s):  
Emad Al-Heety
Keyword(s):  
Moment Tensor ◽  
Focal Depth ◽  
Seismic Hazard Assessment ◽  
B Value ◽  
Strike Slip ◽  
Focal Mechanisms ◽  
Likelihood Method ◽  
Centroid Moment Tensor ◽  
B Values ◽  
Completeness Magnitude

The earthquake size distribution (b-value) is a significant factor to recognize the seismic activity, seismotectonic, and seismic hazard assessment. In the current work, the connection of the b-constant value with the focal depth and mechanism was studied. The effect of the study scale (global, regional and local) on the dependence of b-value on the focal mechanisms was investigated. The database is quoted from the Global Centroid Moment Tensor catalog. The selected earthquakes are the shallow normal, reverse and strike-slip events. The completeness magnitude (Mc) is 5.3. The maximum likelihood method is utilized to compute the b-value. The obtained results show that the b-value is decreasing with depth to range 10-20 km, then increases to the depth of 40km. The turning point of b-value (increasing of b-value) locates at the depth of the transition brittle-ductile zone. Globally and regionally, low, moderate, and high b-values are associated with reverse, strike-slip, and normal focal mechanisms, respectively, while locally, the relation between b-values and focal mechanisms shows different association trends, such as low, moderate, and high b-values are associated with normal, strike-slip, and reverse focal mechanisms and so on.

gCAPjoint, A Software Package for Full Moment Tensor Inversion of Moderately Strong Earthquakes with Local and Teleseismic Waveforms

2020 ◽  
Vol 91 (6) ◽  
pp. 3550-3562
Author(s):  
Qipeng Bai ◽  
Sidao Ni ◽  
Risheng Chu ◽  
Zhe Jia
Keyword(s):  
Software Package ◽  
Epicentral Distance ◽  
Joint Inversion ◽  
Moment Tensor ◽  
Centroid Moment Tensor ◽  
Waveform Data ◽  
Strong Earthquakes ◽  
Moment Tensors ◽  
Seismic Networks ◽  
Full Moment Tensor

Abstract Earthquake moment tensors and focal depths are crucial to assessing seismic hazards and studying active tectonic and volcanic processes. Although less powerful than strong earthquakes (M 7+), moderately strong earthquakes (M 5–6.5) occur more frequently and extensively, which can cause severe damages in populated areas. The inversion of moment tensors is usually affected by insufficient local waveform data (epicentral distance <5°) in sparse seismic networks. It would be necessary to combine local and teleseismic data (epicentral distance 30°–90°) for a joint inversion. In this study, we present the generalized cut-and-paste joint (gCAPjoint) algorithm to jointly invert full moment tensor and centroid depth with local and teleseismic broadband waveforms. To demonstrate the effectiveness and explore the limitations of this algorithm, we perform case studies on three earthquakes with different tectonic settings and source properties. Comparison of our results with global centroid moment tensor and other catalog solutions illustrates that both non-double-couple compositions of the focal mechanisms and centroid depths can be reliably recovered for very shallow (<10  km) earthquakes and intermediate-depth events with this software package.

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