An Earthquake Source Spectrum Model Considering Rupture Directivity and Its Application for Obtaining Green’s Functions

2020 ◽  
Vol 110 (6) ◽  
pp. 2711-2727
Author(s):  
Shota Shimmoto
Keyword(s):  
Ground Motion ◽  
Green's Functions ◽  
Green’S Functions ◽  
Ground Motions ◽  
Source Spectrum ◽  
Rupture Directivity ◽  
Small Earthquake ◽  
Finite Fault ◽  
Ground Motion Records ◽  
Spectrum Model

ABSTRACT A small earthquake with strong rupture directivity is inappropriate to use as a point source when estimating ground motion. A source spectrum model is proposed to remove the effects of rupture directivity and finite fault size from observed earthquakes. This model is developed by using a kinematic source model of a rectangular fault with bilateral-bidirectional rupture propagation. Its amplitude spectrum is modeled to decay as ω−2 at high frequency and is approximated by its envelope to make deconvolution a stable operation. The effectiveness of the proposed spectrum model is demonstrated through application to the two aftershocks of Mw 4.0 and Mw 5.5 observed following the 2016 Kumamoto earthquake. These aftershocks had similar focal mechanisms and were located near to each other. A method to estimate the source parameters by using the proposed spectrum model is presented and its effectiveness is demonstrated. The deconvolution of the ground-motion records using a suitable source spectrum model gives us the Green’s function. The amplitude spectra of the Green’s functions obtained from both observed aftershock events are shown to be consistent. The far-field ground motions are simulated by using the Green’s functions. The simulated ground motions match well with the observed ones. Simulation of the ground motions by using the Green’s functions obtained from the deconvolution of ground-motion records by the proposed spectrum model has an advantage compared to the use of small earthquake records as empirical Green’s functions (EGFs). Specifically, this approach reduces the variation in ground-motion simulation results due to the choice of different EGFs.

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.

Analysis of Near-Source Ground Motion from the 2019 Ridgecrest Earthquake Sequence

2020 ◽  
Vol 110 (4) ◽  
pp. 1495-1505 ◽  
Author(s):  
Georgios Baltzopoulos ◽  
Lucia Luzi ◽  
Iunio Iervolino
Keyword(s):  
Ground Motion ◽  
Earthquake Engineering ◽  
Ground Motions ◽  
Strong Motion ◽  
Rupture Directivity ◽  
Surface Rupture ◽  
Ground Acceleration ◽  
Ground Motion Records ◽  
Manual Classification ◽  
Forward Rupture Directivity

ABSTRACT The Ridgecrest seismic sequence began on 4 July 2019 in California, on a hitherto relatively unmapped orthogonal cross-faulting system, causing mainly nonstructural or liquefaction-related damage to buildings in the vicinity of Ridgecrest and Trona, and also causing substantial surface rupture. The present study considers the near-source ground-acceleration recordings collected during the two principal events of the sequence—the 4 July moment-magnitude M 6.4 foreshock and the 6 July M 7.1 mainshock—to identify pulse-like ground motions, which may have arisen due to forward rupture directivity. Pulse-like seismic input is of particular interest to earthquake engineering due to its peculiar spectral shape and possibly increased damaging potential, and expanding the strong-motion databases with such records is a topical issue. In this context, a pulse identification methodology is implemented, partially based on computer-aided signal processing, but also involving manual classification. Nine ground-motion records were classified as pulse-like by this procedure. Further investigation led to the conclusion that, for some of these records, the impulsive characteristics could most likely be attributable to forward rupture directivity, whereas for others fling step may have also been an issue. Finally, clear signs of directionality were observed in these ground motions at periods near the pulse duration, manifesting as a polarization of the spectral ordinates toward the orientation of the impulsive component.

scholarly journals A technique for simulating strong ground motion using hybrid Green's function

1998 ◽  
Vol 88 (2) ◽  
pp. 357-367 ◽  
Author(s):  
Katsuhiro Kamae ◽  
Kojiro Irikura ◽  
Arben Pitarka
Keyword(s):  
Green’S Function ◽  
Ground Motion ◽  
Green's Function ◽  
Green's Functions ◽  
Strong Ground Motion ◽  
Green’S Functions ◽  
Ground Motions ◽  
Large Earthquake ◽  
Long Period ◽  
Strong Ground

Abstract A method for simulating strong ground motion for a large earthquake based on synthetic Green's function is presented. We use the synthetic motions of a small event as Green's functions instead of observed records of small events. Ground motions from small events are calculated using a hybrid scheme combining deterministic and stochastic approaches. The long-period motions from the small events are deterministically calculated using the 3D finite-difference method, whereas the high-frequency motions from them are stochastically simulated using Boore's method. The small-event motions are synthesized summing the long-period and short-period motions after passing them through a pair of matched filters to follow the omega-squared source model. We call the resultant time series “hybrid Green's functions” (HGF). Ground motions from a large earthquake are simulated by following the empirical Green's function (EGF) method. We demonstrate the effectiveness of the method at simulating ground motion from the 1995 Hyogo-ken Nanbu earthquake (Mw 6.9).

scholarly journals Simulation of non-stationary stochastic ground motions based on recent Italian earthquakes

2021 ◽  
Author(s):  
Fabio Sabetta ◽  
Antonio Pugliese ◽  
Gabriele Fiorentino ◽  
Giovanni Lanzano ◽  
Lucia Luzi
Keyword(s):  
Ground Motion ◽  
Ground Motions ◽  
Strong Motion ◽  
Stochastic Simulations ◽  
Model Parameters ◽  
Motion Model ◽  
Arias Intensity ◽  
Time Frequency ◽  
Ground Motion Model ◽  
Ground Motion Records

AbstractThis work presents an up-to-date model for the simulation of non-stationary ground motions, including several novelties compared to the original study of Sabetta and Pugliese (Bull Seism Soc Am 86:337–352, 1996). The selection of the input motion in the framework of earthquake engineering has become progressively more important with the growing use of nonlinear dynamic analyses. Regardless of the increasing availability of large strong motion databases, ground motion records are not always available for a given earthquake scenario and site condition, requiring the adoption of simulated time series. Among the different techniques for the generation of ground motion records, we focused on the methods based on stochastic simulations, considering the time- frequency decomposition of the seismic ground motion. We updated the non-stationary stochastic model initially developed in Sabetta and Pugliese (Bull Seism Soc Am 86:337–352, 1996) and later modified by Pousse et al. (Bull Seism Soc Am 96:2103–2117, 2006) and Laurendeau et al. (Nonstationary stochastic simulation of strong ground-motion time histories: application to the Japanese database. 15 WCEE Lisbon, 2012). The model is based on the S-transform that implicitly considers both the amplitude and frequency modulation. The four model parameters required for the simulation are: Arias intensity, significant duration, central frequency, and frequency bandwidth. They were obtained from an empirical ground motion model calibrated using the accelerometric records included in the updated Italian strong-motion database ITACA. The simulated accelerograms show a good match with the ground motion model prediction of several amplitude and frequency measures, such as Arias intensity, peak acceleration, peak velocity, Fourier spectra, and response spectra.

Deterministic 3D Ground-Motion Simulations (0–5 Hz) and Surface Topography Effects of the 30 October 2016 Mw 6.5 Norcia, Italy, Earthquake

2021 ◽  
Author(s):  
Arben Pitarka ◽  
Aybige Akinci ◽  
Pasquale De Gori ◽  
Mauro Buttinelli
Keyword(s):  
Surface Topography ◽  
Ground Motion ◽  
Seismic Station ◽  
Ground Motions ◽  
Peak Ground Velocity ◽  
Earth Model ◽  
Rupture Directivity ◽  
Epicentral Area ◽  
Near Fault ◽  
Local Topography

ABSTRACT The Mw 6.5 Norcia, Italy, earthquake occurred on 30 October 2016 and caused extensive damage to buildings in the epicentral area. The earthquake was recorded by a network of strong-motion stations, including 14 stations located within a 5 km distance from the two causative faults. We used a numerical approach for generating seismic waves from two hybrid deterministic and stochastic kinematic fault rupture models propagating through a 3D Earth model derived from seismic tomography and local geology. The broadband simulations were performed in the 0–5 Hz frequency range using a physics-based deterministic approach modeling the earthquake rupture and elastic wave propagation. We used SW4, a finite-difference code that uses a conforming curvilinear mesh, designed to model surface topography with high numerical accuracy. The simulations reproduce the amplitude and duration of observed near-fault ground motions. Our results also suggest that due to the local fault-slip pattern and upward rupture directivity, the spatial pattern of the horizontal near-fault ground motion generated during the earthquake was complex and characterized by several local minima and maxima. Some of these local ground-motion maxima in the near-fault region were not observed because of the sparse station coverage. The simulated peak ground velocity (PGV) is higher than both the recorded PGV and predicted PGV based on empirical models for several areas located above the fault planes. Ground motions calculated with and without surface topography indicate that, on average, the local topography amplifies the ground-motion velocity by 30%. There is correlation between the PGV and local topography, with the PGV being higher at hilltops. In contrast, spatial variations of simulated PGA do not correlate with the surface topography. Simulated ground motions are important for seismic hazard and engineering assessments for areas that lack seismic station coverage and historical recordings from large damaging earthquakes.

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.

An Improved Source Model for Simulation Near-Field Strong Ground Motion Acceleration Time History

2013 ◽  
Vol 438-439 ◽  
pp. 1474-1480
Author(s):  
Ju Fang Zhong ◽  
Long Wei Zhang ◽  
Jun Wei Liang
Keyword(s):  
Ground Motion ◽  
Strong Ground Motion ◽  
Response Spectrum ◽  
Near Field ◽  
Time History ◽  
Source Spectrum ◽  
Acceleration Time ◽  
Acceleration Time History ◽  
Spectrum Model ◽  
Strong Ground

The key to near-field strong ground motion simulation based on stochastic finite fault method is to determine the spectrum of ground motion. We present an improved source spectrum model for simulation near-field strong ground motion acceleration time history. We combine Masudas source spectrum model with scaling factor Hij to keep radiation energy conservation and reflect the energy decrease with frequency at low to mid frequencies. We calculate the Fourier amplitude spectrum Fa, accelerate response spectrum Sa, velocity response spectrum Sv and displacement response spectrum Sd of simulation time histories. By comparative analysis of the laws of spectrum values (Fa, Sa, Sv, Sd) with the variation of frequency or period, we discusses the effects of sub-fault dividing scheme, the method of determining scale factor and source spectrum model on spectrum values (Fa, Sa, Sv, Sd). The results show that sub-fault dividing scheme has slightly effect on the model presented in this paper, and the model enable to reflect the sink laws of source spectrum value in mid-to-low frequencies well. We demonstrate that the improved model is superior to other commonly used models.

Hybrid Simulation of Near-Fault Ground Motion for a Potential Mw 7 Earthquake in Lebanon

2021 ◽  
Vol 111 (5) ◽  
pp. 2441-2462 ◽  
Author(s):  
Rosemary Fayjaloun ◽  
Mayssa Dabaghi ◽  
Cecile Cornou ◽  
Mathieu Causse ◽  
Yang Lu ◽  
...  
Keyword(s):  
Ground Motion ◽  
Velocity Structure ◽  
Ground Motions ◽  
Seismic Energy ◽  
Velocity Model ◽  
Historical Seismicity ◽  
Stochastic Simulations ◽  
Hybrid Technique ◽  
Rupture Directivity ◽  
Near Fault

ABSTRACT Lebanon is a densely populated country crossed by major faults. Historical seismicity shows the potential of earthquakes with magnitudes >7, but large earthquakes have never been instrumentally recorded in Lebanon. Here, we propose a method to simulate near-fault broadband ground motions for a potential Mw 7 earthquake on the Yammouneh fault (YF)—the largest branch of the Dead Sea Transform fault that bisects Lebanon from north to south. First, we performed the first 3D tomography study of Lebanon using ambient noise correlation, which showed that Lebanon could be approximated by a 1D velocity structure for low-frequency (LF) ground-motion simulation purposes. Second, we generated suites of kinematic rupture models on the YF, accounting for heterogeneity of the rupture process, and uncertainty of the rupture velocity and hypocenter location. The radiated seismic energy was next propagated in the inferred 1D velocity model to obtain suites of LF ground motions (<1 Hz) at four hypothetical near-fault seismic stations. These LF simulations included the main features of near-fault ground motions, such as the impulsive character of ground velocity due to the rupture directivity or fling-step effects (so-called pulse-like ground motions). Third, to obtain broadband ground motions (up to 10 Hz), we proposed a hybrid technique that combined the simulated LF ground motions with high-frequency (HF) stochastic simulations, which were empirically calibrated using a worldwide database of near-fault recordings. Contrary to other hybrid approaches, in which the LF and HF motions are generally computed independently, the characteristics of stochastic HF ground motions were conditioned on those of LF ground motions (namely on the characteristics of the velocity pulse, if it existed, or on the absence of a pulse). The simulated peak ground accelerations were in agreement with the ones reported in the Next Generation Attenuation-West2 (NGA-West2) database for similar magnitude and distances and with three NGA-West2 ground-motion prediction equations.

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