Estimating high frequency energy radiation of large earthquakes by image deconvolution back-projection

2016 ◽  
Vol 449 ◽  
pp. 155-163 ◽  
Author(s):  
Dun Wang ◽  
Nozomu Takeuchi ◽  
Hitoshi Kawakatsu ◽  
Jim Mori
Keyword(s):  
High Frequency ◽  
Image Deconvolution ◽  
Back Projection ◽  
Energy Radiation ◽  
Large Earthquakes

scholarly journals Estimating Rupture Front of Large Earthquakes Using a Novel Multi-Array Back-Projection Method

2021 ◽  
Vol 9 ◽  
Author(s):  
Hailin Du
Keyword(s):  
Projection Method ◽  
High Frequency ◽  
Epicentral Distance ◽  
Temporal Distribution ◽  
Small Error ◽  
Back Projection ◽  
Positioning Accuracy ◽  
Complex Source ◽  
Back Azimuth ◽  
Large Earthquakes

A ruptured front obtained from high-frequency energy radiation is the key to understand the complex source. It is commonly observed that rupture fronts derived from different arrays often show some variations due to the obvious difference of the positioning accuracy of the far-field array between the azimuth and the epicentral distance. We developed a new multi-array back-projection method based on the classical back-projection method and applied the method to the 2015 MW7.8 Nepal earthquake. The back azimuth information with small error is separated from the classical back-projection results, and the azimuth intersection of multiple arrays is used to obtain more accurate spatial and temporal distribution information of the source rupture fronts.

Multi-Array Multi-Phase Back-Projection: Improving the imaging of earthquake rupture complexities

2021 ◽  
Author(s):  
Felipe Vera ◽  
Frederik Tilmann ◽  
Joachim Saul
Keyword(s):  
High Frequency ◽  
Solomon Islands ◽  
P Wave ◽  
Back Projection ◽  
Dynamic Triggering ◽  
Array Configuration ◽  
Megathrust Earthquakes ◽  
Rupture Length ◽  
Multi Phase ◽  
Large Earthquakes

<p>We present a teleseismic earthquake back-projection method parameterized with multiple arrays and combined P and pP waveforms, improving the spatiotemporal resolvability of rupture complexity. The contribution of each array to the rupture image is weighted depending on the multi-array configuration. Depth phases also contribute effectively to earthquakes at 40 km depth or deeper.</p><p>We examine 31 large earthquakes with moment magnitude greater than 7.5 from 2010-2020, which were back-projected in the 0.5-2.0 Hz band, giving access to the high-frequency rupture propagation. An algorithm estimates rupture length, directivity, and speed based on the back-projection results.</p><p>Thrust and normal earthquakes showed similar magnitude-dependent lengths and consistent subshear ruptures, while strike-slip earthquakes presented longer ruptures (relative to their magnitude) and frequently reached supershear speeds. The back-projected lengths provided scaling relations to derive high-frequency rupture lengths from moment magnitudes. The results revealed complex rupture behavior, for example, bilateral ruptures (e.g., the 2017 Mw 7.8 Komandorsky Islands earthquake), evidence of dynamic triggering by a P wave (e.g., the 2016 Mw 7.9 Solomon Islands earthquake), and encircling asperity ruptures (e.g., the 2010 Mw 7.8 Mentawai and 2015 Mw 8.4 Illapel earthquakes). The latter is particularly prevalent in subduction megathrust earthquakes, with down-dip, up-dip, double encircling, and segmented patterns. The automated choice of array weighting and the extraction of basic rupture parameters makes the approach well suited for near-real-time earthquake monitoring.</p>

Spatial distribution of high-frequency energy radiation on the fault of the 1995 Hyogo-Ken Nanbu, Japan, earthquake (MW 6.9) on the basis of the seismogram envelope inversion

1999 ◽  
Vol 89 (1) ◽  
pp. 22-35 ◽  
Author(s):  
Hisashi Nakahara ◽  
Haruo Sato ◽  
Masakazu Ohtake ◽  
Takeshi Nishimura
Keyword(s):  
Spatial Distribution ◽  
Wave Energy ◽  
High Frequency ◽  
Fault Plane ◽  
Time Window ◽  
Source Region ◽  
Inversion Method ◽  
S Wave ◽  
Energy Radiation ◽  
Initial Rupture

Abstract We studied the generation and propagation of high-frequency (above 1 Hz) S-wave energy from the 1995 Hyogo-Ken Nanbu (Kobe), Japan, earthquake (MW 6.9) by analyzing seismogram envelopes of the mainshock and aftershocks. We first investigated the propagation characteristics of high-frequency S-wave energy in the heterogeneous lithosphere around the source region. By applying the multiple lapse time window analysis method to aftershock records, we estimated two parameters that quantitatively characterize the heterogeneity of the medium: the total scattering coefficient and the intrinsic absorption of the medium for S waves. Observed envelopes of aftershocks were well reproduced by the envelope Green functions synthesized based on the radiative transfer theory with the obtained parameters. Next, we applied the envelope inversion method to 13 strong-motion records of the mainshock. We divided the mainshock fault plane of 49 × 21 km into 21 subfaults of 7 × 7 km square and estimated the spatial distribution of the high-frequency energy radiation on that plane. The average constant rupture velocity and the duration of energy radiation for each subfault were determined by grid searching to be 3.0 km/sec and 5.0 sec, respectively. Energy radiated from the whole fault plane was estimated as 4.9 × 1014 J for 1 to 2 Hz, 3.3 × 1014 J for 2 to 4 Hz, 1.5 × 1014 J for 4 to 8 Hz, 8.9 × 1012 J for 8 to 16 Hz, and 9.8 × 1014 J in all four frequency bands. We found that strong energy was mainly radiated from three regions on the mainshock fault plane: around the initial rupture point, near the surface at Awaji Island, and a shallow portion beneath Kobe. We interpret that energetic portions were associated with rupture acceleration, a fault surface break, and rupture termination, respectively.

High-Frequency Spectral Decay Characteristics of Seismic Records of Inland Crustal Earthquakes in Japan: Evaluation of the fmax and κ Models

2020 ◽  
Vol 110 (2) ◽  
pp. 452-470
Author(s):  
Masato Tsurugi ◽  
Reiji Tanaka ◽  
Takao Kagawa ◽  
Kojiro Irikura
Keyword(s):  
Ground Motion ◽  
High Frequency ◽  
Strong Ground Motion ◽  
Cutoff Frequency ◽  
Source Model ◽  
Power Coefficient ◽  
Crustal Earthquakes ◽  
Log Linear ◽  
Large Earthquakes ◽  
Strong Ground

ABSTRACT We examined high-frequency spectral decay characteristics of ground motions for inland crustal earthquakes in Japan, which are important in strong ground motion predictions. We examined 105 earthquakes (Mw 3.3–7.1), including seven large earthquakes (Mw 5.9–7.1). Spectral decay characteristics were accurately evaluated assuming the ω-squared source model and using two approaches: the fmax model (commonly used in Japan), described by the cutoff frequency fmax and the power coefficient of spectral decay s, and the κ model (commonly used in worldwide), the exponential spectral decay model, described by the parameter κ and the specific frequency fE at which a spectrum starts to decrease linearly with increasing frequency in log–linear space. For large earthquakes, we estimated fmax to range from 6.5 to 9.9 Hz and s from 0.78 to 1.60 in the fmax model, and κ to range from 0.014 to 0.051 s and fE from 2 to 4.5 Hz in the κ model. In both approaches, we found that the spectral decay characteristics are regionally dependent. fmax in the fmax model and fE in the κ model tended to be smaller for large earthquakes than for moderate and small earthquakes, clearly demonstrating a seismic moment dependency. We confirmed positive correlations between equivalent parameters of the two approaches, that is, between s and κ and between fmax and fE. Moreover, we found that both approaches are appropriate for evaluating spectral decay characteristics, as long as the spectral decay parameters are appropriately evaluated by comparison with observed spectra. We examined the effects of the spectral decay characteristics on strong ground motion predictions, and demonstrated that simulated motions corrected using the fmax model and those corrected using the κ model are almost the same. The results presented in this article contribute to improving predictions of high-frequency strong ground motion.

scholarly journals Sources of uncertainties and artifacts in back-projection results

2019 ◽  
Author(s):  
Zeng Hongyu ◽  
Wei Shengji ◽  
Wu Wenbo
Keyword(s):  
High Frequency ◽  
Synthetic Data ◽  
Water Layer ◽  
Focal Mechanisms ◽  
Coda Waves ◽  
Back Projection ◽  
Common Procedure ◽  
Frequency Dependent ◽  
Synthetic Test ◽  
The Impact

Summary Back-projecting high-frequency (HF) waves is a common procedure for imaging rupture processes of large earthquakes (i.e. Mw > 7.0). However, obtained back-projection (BP) results could suffer from large uncertainties since high-frequency seismic waveforms are strongly affected by factors like source depth, focal mechanisms, and the Earth's 3D velocity structures. So far, these uncertainties have not been thoroughly investigated. Here, we use synthetic tests to investigate the influencing factors for which scenarios with various source and/or velocity set-ups are designed, using either Tohoku-Oki (Japan), Kaikoura (New Zealand), Java/Wharton Basin (Indonesia) as test areas. For the scenarios, we generate either 1D or 3D teleseismic synthetic data, which are then back-projected using a representative BP method, MUltiple SIgnal Classification (MUSIC). We also analyze corresponding real cases to verify the synthetic test results. The Tohoku-Oki scenario shows that depth phases of a point source can be back-projected as artifacts at their bounce points on the earth's surface, with these artifacts located far away from the epicenter if earthquakes occur at large depths, which could significantly contaminate BP images of large intermediate-depth earthquakes. The Kaikoura scenario shows that for complicated earthquakes, composed of multiple sub-events with varying focal mechanisms, BP tends to image sub-events emanating large amplitude coherent waveforms, while missing sub-events whose P nodal directions point to the arrays, leading to discrepancies either between BP images from different arrays, or between BP images and other source models. Using the Java event, we investigate the impact of 3D source-side velocity structures. The 3D bathymetry together with a water layer can generate strong and long-lasting coda waves, which are mirrored as artifacts far from the true source location. Finally, we use a Wharton Basin outer-rise event to show that the wavefields generated by 3D near trench structures contain frequency-dependent coda waves, leading to frequency-dependent BP results. In summary, our analyses indicate that depth phases, focal mechanism variations, and 3D source-side structures can affect various aspects of BP results. Thus, we suggest that target-oriented synthetic tests, for example, synthetic tests for subduction earthquakes using more realistic 3D source-side velocity structures, should be conducted to understand the uncertainties and artifacts before we interpret detailed BP images to infer earthquake rupture kinematics and dynamics.

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