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>

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

2020 ◽  
Author(s):  
Felipe Vera ◽  
Frederik Tilmann ◽  
Joachim Saul
Keyword(s):  
High Frequency ◽  
Strong Motion ◽  
Back Projection ◽  
Coseismic Slip ◽  
Seismic Arrays ◽  
Motion Data ◽  
Successful Recovery ◽  
Short Period ◽  
Multi Phase ◽  
Rupture Imaging

<p><span>We present a back-projection method capable of being parameterized with multiples arrays. The rupture imaging is weighted to restrict uncertainties induced by non-symmetric azimuthal coverage of seismic arrays. The strategy also exploits the differences in time delays between </span><em><span>P</span></em><span> and depth phase (</span><em><span>pP)</span></em><span> waveforms by assuming them as proxies of the rupture that can be simultaneously back-projected. Surprisingly, this helps to improve the final results, even when depth phases overlap with the direct arrivals due to the rupture time exceeding the <em>pP-P</em> delay. Thus, the approach heightens the spatiotemporal resolvability enough to image rupture complexities. The rupture image of two large events demonstrates its robustness. The first one is the 14 November 2007 Mw 7.7 Tocopilla earthquake in northern Chile. The high-frequency rupture (0.5 - 2.0 Hz) encircles two asperities while the short-period energy radiated predominates up-dip of the coseismic slip. We propose the contribution of asperity rupture complexities and along-dip barriers to high-frequency emissions beyond the megathrust frictional structure. The second one is the Mw 7.5 Palu strike-slip earthquake, which occurred on 28 September 2018 in Sulawesi island. The back-projection reveals a prominent supershear rupture at a speed of 4.5 km/s. The result correlates with space geodesy data highlighting the successful recovery of fault structures. Finally, we discuss the potential and challenges of automating this analysis for near-real-time applications</span>, including near-source back-projection with strong-motion data.</p>

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.

Source dynamics of the 1979 Imperial Valley earthquake from near-source observations (of ground acceleration and velocity)

1982 ◽  
Vol 72 (6A) ◽  
pp. 1957-1968
Author(s):  
Mansour Niazi
Keyword(s):  
Particle Acceleration ◽  
Particle Velocity ◽  
High Frequency ◽  
Observation Point ◽  
P Wave ◽  
Imperial Valley ◽  
Ground Acceleration ◽  
Data Set ◽  
Ground Shaking ◽  
Fault Surface

abstract Two sets of observations obtained during the 15 October 1979 Imperial Valley earthquake, MS 6.9, are presented. The data suggest different dynamic characteristics of the source when viewed in different frequency bands. The first data set consists of the observed residuals of the horizontal peak ground accelerations and particle velocity from predicted values within 50 km of the fault surface. The residuals are calculated from a nonlinear regression analysis of the data (Campbell, 1981) to the following empirical relationships, PGA = A 1 ( R + C 1 ) − d 1 , PGV = A 2 ( R + C 2 ) − d 2 in which R is the closest distance to the plane of rupture. The so-calculated residuals are correlated with a positive scalar factor signifying the focusing potential at each observation point. The focusing potential is determined on the basis of the geometrical relation of the station relative to the rupture front on the fault plane. The second data set consists of the acceleration directions derived from the windowed-time histories of the horizontal ground acceleration across the El Centro Differential Array (ECDA). The horizontal peak velocity residuals and the low-pass particle acceleration directions across ECDA require the fault rupture to propagate northwestward. The horizontal peak ground acceleration residuals and the high-frequency particle acceleration directions, however, are either inconclusive or suggest an opposite direction for rupture propagation. The inconsistency can best be explained to have resulted from the incoherence of the high-frequency radiation which contributes most effectively to the registration of PGA. A test for the sensitivity of the correlation procedure to the souce location is conducted by ascribing the observed strong ground shaking to a single asperity located 12 km northwest of the hypocenter. The resulting inconsistency between the peak acceleration and velocity observations in relation to the focusing potential is accentuated. The particle velocity of Delta Station, Mexico, in either case appears abnormally high and disagrees with other observations near the southeastern end of the fault trace. From the observation of a nearly continuous counterclockwise rotation of the plane of P-wave particle motion at ECDA, the average rupture velocity during the first several seconds of source activation is estimated to be 2.0 to 3.0 km/sec. A 3 km upper bound estimate of barrier dimensions is tentatively made on the basis of the observed quasiperiodic variation of the polarization angles.

P-wave spectra for ML 5 foreshocks, aftershocks, and isolated earthquakes near Parkfield, California

1981 ◽  
Vol 71 (2) ◽  
pp. 423-436
Author(s):  
Willian H. Bakun ◽  
Thomas V. McEvilly
Keyword(s):  
Stress Drop ◽  
High Stress ◽  
P Wave ◽  
Wave Radiation ◽  
Focal Region ◽  
Wave Spectra ◽  
Rupture Length ◽  
Main Shocks ◽  
Relative Stress ◽  
Fault Trace

abstract Wood-Anderson seismograms recorded at Mount Hamilton (MHC, 185 km, 327°), Santa Barbara (SBC, 180 km, 158°), and Tinemaha (TIN, 240 km, 56°) provide data for comparing P-wave spectra for two immediate (17-min) foreshocks, one early (55-hr) foreshock, two aftershocks, and two “isolated” Parkfield earthquakes. All are ML 5.0 shocks with epicenters within 7 km of the common epicenter of the 1934 and 1966 Parkfield main shocks. The set of events is well suited for testing the hypothesis that foreshocks are high-stress-drop sources. Calculated stress drops are controlled by source directivity at azimuths aligned with the fault break (at MHC and SBC). P-wave radiation from the three foreshocks is focused along one fault trace azimuth, suggesting that foreshock sources are characterized by pronounced unilateral rupture expansion. At TIN, broadside to the fault where directivity has minimum effect on calculated relative stress drop, the two immediate foreshocks are higher stress-drop sources. The early foreshock is a low-to-average stress-drop source, indicating the possibility that stress concentration is a rapidly occurring phenomenon in rupture nucleation. Alternatively, the stress field is highly variable on the scale of 2 to 3 km in the focal region of an impending earthquake with a rupture length of 20 to 30 km.

scholarly journals Pulse-like partial ruptures and high-frequency radiation at creeping-locked transition during megathrust earthquakes

2017 ◽  
Vol 44 (16) ◽  
pp. 8345-8351 ◽  
Author(s):  
Sylvain Michel ◽  
Jean-Philippe Avouac ◽  
Nadia Lapusta ◽  
Junle Jiang
Keyword(s):  
High Frequency ◽  
Megathrust Earthquakes ◽  
Frequency Radiation ◽  
High Frequency Radiation

Propagation of high-frequency (4- to 50-Hz) P waves in the northeastern United States

1995 ◽  
Vol 85 (4) ◽  
pp. 1244-1248
Author(s):  
Eric P. Chael ◽  
Patrick J. Leahy ◽  
Jerry A. Carter ◽  
Noël Barstow ◽  
Paul W. Pomeroy
Keyword(s):  
United States ◽  
Decay Rate ◽  
High Frequency ◽  
P Wave ◽  
Wave Spectra ◽  
Northeastern United States ◽  
P Waves ◽  
Geometric Spreading ◽  
Frequency Independent

Abstract We have measured the decay rate of high-frequency (4- to 50-Hz) P waves in the northeastern United States. We analyzed signals from 28 explosions of a 1988 USGS/AFGL/GSC refraction survey recorded at distances between 30 and 400 km. Over this range, the decay rate steadily increases from Δ−2 at 10 Hz to Δ−4 at 45 Hz. If one assumes geometric spreading of Δ−1.3, then the remaining decay is consistent with a nearly frequency-independent Q of about 1000. The results provide a useful parameterization for predicting P-wave spectra at near-regional ranges.

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