scholarly journals SOURCE LOCATION DEPENDENCE ON GREEN’S FUNCTIONS AND THE EFFECTS OF THE ARRANGEMENT OF STRONG MOTION GENERATION AREA ON COMPUTED GROUND MOTIONS

2021 ◽  
Vol 86 (783) ◽  
pp. 696-705
Author(s):  
Yoshihiro TERASHIMA ◽  
Nobuo FUKUWA
Keyword(s):  
Green's Functions ◽  
Green’S Functions ◽  
Ground Motions ◽  
Strong Motion ◽  
Source Location ◽  
Motion Generation ◽  
Strong Motion Generation Area

Rupture Process of the Mainshock of the 2019 Ridgecrest Earthquake Sequence from Waveform Inversion with Empirical Green’s Functions

2021 ◽  
Author(s):  
Shuang-Lan Wu ◽  
Atsushi Nozu ◽  
Yosuke Nagasaka
Keyword(s):  
Green's Functions ◽  
Green’S Functions ◽  
Ground Motions ◽  
Strong Motion ◽  
Rupture Process ◽  
Earthquake Sequence ◽  
Slip Model ◽  
Near Fault ◽  
Empirical Green’S Functions ◽  
Empirical Green's Functions

ABSTRACT The 2019 Mw 7.1 mainshock of the Ridgecrest earthquake sequence, which was the first event exceeding Mw 7.0 in California since the 1999 Hector Mine earthquake, caused near-fault ground motions exceeding 0.5g and 70  cm/s. In this study, the rupture process and the generation mechanism of strong ground motions of the mainshock were investigated through waveform inversions of strong-motion data in the frequency range of 0.2–2.0 Hz using empirical Green’s functions (EGFs). The results suggest that the mainshock involved two large slip regions: the primary one with a maximum slip of approximately 4.4 m was centered ∼3  km northwest of the hypocenter, which was slightly shallower than the hypocenter, and the secondary one was centered ∼25  km southeast of the hypocenter. Outside these regions, the slip was rather small and restricted to deeper parts of the fault. A relatively small rupture velocity of 2.1  km/s was identified. The robustness of the slip model was examined by conducting additional inversion analyses with different combinations of EGF events and near-fault stations. In addition, using the preferred slip model, we synthesized strong motions at stations that were not used in the inversion analyses. The synthetic waveforms captured the timing of the main phases of observed waveforms, indicating the validity of the major spatiotemporal characteristics of the slip model. Our large slip regions are also generally visible in the models proposed by other researchers based on different datasets and focusing on lower frequency ranges (generally lower than 0.5 Hz). In particular, two large slip regions in our model are very consistent with two of the four subevents identified by Ross et al. (2019), which may indicate that part of the large slip regions that generated low-frequency ground motions also generated high-frequency ground motions up to 2.0 Hz during the Ridgecrest mainshock.

Modeling of strong motion generation area of the Uttarkashi earthquake using modified semiempirical approach

2014 ◽  
Vol 73 (3) ◽  
pp. 2041-2066 ◽  
Author(s):  
Sandeep ◽  
A. Joshi ◽  
Kamal ◽  
Parveen Kumar ◽  
Pushpa Kumari
Keyword(s):  
Strong Motion ◽  
Motion Generation ◽  
Strong Motion Generation Area ◽  
Semiempirical Approach

Stability of earthquake ground motion synthesized by using different small-event records as empirical Green's functions

1990 ◽  
Vol 80 (6A) ◽  
pp. 1433-1455 ◽  
Author(s):  
K. Dan ◽  
T. Watanabe ◽  
T. Tanaka ◽  
R. Sato
Keyword(s):  
Ground Motion ◽  
Green's Functions ◽  
Green’S Functions ◽  
Ground Motions ◽  
Source Parameters ◽  
Earthquake Ground Motion ◽  
Source Spectrum ◽  
Similarity Relations ◽  
Coefficients Of Variation ◽  
Synthesis Procedure

Abstract The semi-empirical method, in which small-event records are used as Green's functions to synthesize strong ground motions from a large earthquake, has become one of the most practical methods for generating the input ground motion for earthquake-resistant design of structures. The stability of the synthesized ground motions was examined in the applicability for engineering purposes. The accelerograms from the 1980 Izu-Hanto-Toho-Oki, Japan, earthquake with a magnitude of 6.7 were simulated by using the records from 17 foreshocks and aftershocks with magnitudes of 3.4 to 4.9. The syntheses were carried out for each small-event record and 17 results are obtained. The coefficients of variation (percentages of the standard deviations to the mean values) of the ratios of the synthesized PGA, PGV and SI to the observed ones were found to be 40 to 80 per cent, which consisted of 20 to 30 per cent caused by our synthesis procedure itself, 30 to 40 per cent caused by the approximation of the source spectrum for each small event by the ω-square model, and 0 to 70 per cent caused by the similarity relations used to obtain the source parameters (L, W, D, and σe from the magnitude. Consequently, in order to minimize the variation caused by the modeling of the source spectrum and the similarity relations, we proposed a new synthesis procedure, in which the small-event records were normalized with regard to the source size and then chosen randomly as Green's functions for each element of the fault plane of the main shock. The coefficients of variation of the results by the present new procedure became 15 to 25 per cent much more stable.

scholarly journals Variability in synthetic earthquake ground motions caused by source variability and errors in wave propagation models

2019 ◽  
Vol 219 (1) ◽  
pp. 346-372 ◽  
Author(s):  
Paul Spudich ◽  
Antonella Cirella ◽  
Laura Scognamiglio ◽  
Elisa Tinti
Keyword(s):  
Green's Functions ◽  
Green’S Functions ◽  
Ground Motions ◽  
Broad Band ◽  
Computational Method ◽  
Spatial Covariance ◽  
Rupture Surface ◽  
Earthquake Ground Motions ◽  
Earth Structures ◽  
Rupture Model

SUMMARY Numerical simulations of earthquake ground motions are used both to anticipate the effects of hypothetical earthquakes by forward simulation and to infer the behaviour of the real earthquake source ruptures by the inversion of recorded ground motions. In either application it is necessary to assume some Earth structure that is necessarily inaccurate and to use a computational method that is also inaccurate for simulating the wavefield Green's functions. We refer to these two sources of error as ‘propagation inaccuracies’, which might be considered to be epistemic. We show that the variance of the Fourier spectrum of the synthetic earthquake seismograms caused by propagation inaccuracies is related to the spatial covariance on the rupture surface of errors in the computed Green's functions, which we estimate for the case of the 2009 L'Aquila, Italy, earthquake by comparing erroneous computed Green's functions with observed L'Aquila aftershock seismograms (empirical Green's functions). We further show that the variance of the synthetic seismograms caused by the rupture variability (aleatory uncertainty) is related to the spatial covariance on the rupture surface of aleatory variations in the rupture model, and we investigate the effect of correlated variations in Green's function errors and variations in rupture models. Thus, we completely characterize the variability of synthetic earthquake seismograms induced by errors in propagation and variability in the rupture behaviour. We calculate the spectra of the variance of the ground motions of the L'Aquila main shock caused by propagation inaccuracies for two specific broad-band stations, the AQU and the FIAM stations. These variances are distressingly large, being comparable or in some cases exceeding the data amplitudes, suggesting that the best-fitting L'Aquila rupture model significantly overfits the data and might be seriously in error. If these computed variances are typical, the accuracy of many other rupture models for past earthquakes may need to be reconsidered. The results of this work might be useful in seismic hazard estimation because the variability of the computed ground motion, caused both by propagation inaccuracies and variations in the rupture model, can be computed directly, not requiring laborious consideration of multiple Earth structures.

Sign in / Sign up

Export Citation Format

Share Document