Reducing nonuniqueness in finite source inversion using rotational ground motions

2014 ◽  
Vol 119 (6) ◽  
pp. 4860-4875 ◽  
Author(s):  
M. Bernauer ◽  
A. Fichtner ◽  
H. Igel
Keyword(s):  
Ground Motions ◽  
Source Inversion ◽  
Finite Source

scholarly journals Improved finite-source inversion through joint measurements of rotational and translational ground motions: A theoretical study

2016 ◽  
Author(s):  
Michael Reinwald ◽  
Moritz Bernauer ◽  
Heiner Igel ◽  
Stefanie Donner
Keyword(s):  
Inverse Problem ◽  
Ground Motions ◽  
Source Parameters ◽  
Normal Fault ◽  
Seismic Source ◽  
Vertical Gradient ◽  
Vertical Displacement ◽  
Source Inversion ◽  
Additional Information ◽  
Finite Source

Abstract. With the prospects of seismic equipment being able to measure rotational ground motions in a wide frequency and amplitude range in the near future we engage in the question how this type of ground motion observation can be used to solve the seismic inverse problem. In this paper, we focus on the question, whether finite source inversion can benefit from additional observations of rotational motion. Keeping the overall number of traces constant, we compare observations from a surface seismic network with 44 3-component translational sensors (classic seismometers) with those obtained with 22 6-component sensors (with additional 3-component rotational motions). Synthetic seismograms are calculated for known finite-source properties. The corresponding inverse problem is posed in a probabilistic way using the Shannon information content as measure how the observations constrain the seismic source properties. We minimize the influence of the source receiver geometry around the fault by statistically analyzing six-component (three velocity and three rotation rate) inversions with a random distribution of receivers. The results show that with the 6-C subnetworks the source properties are not only equally well recovered (even that would be benefitial because of the substantially reduced logistics installing half the sensors) but statistically some source properties are almost always better resolved. We assume that this can be attributed to the fact that the (in particular vertical) gradient information is contained in the additional motion components. We compare these effects for strike-slip and normal-faulting type sources and confirm that the increase in inversion quality for kinematic source parameters is even higher for the normal fault. This indicates that the inversion benefits from the additional information provided by the horizontal rotation rates, i.e. information about the vertical displacement gradient.

scholarly journals Improved finite-source inversion through joint measurements of rotational and translational ground motions: a numerical study

Solid Earth ◽  
2016 ◽  
Vol 7 (5) ◽  
pp. 1467-1477 ◽  
Author(s):  
Michael Reinwald ◽  
Moritz Bernauer ◽  
Heiner Igel ◽  
Stefanie Donner
Keyword(s):  
Inverse Problem ◽  
Numerical Study ◽  
Ground Motions ◽  
Source Parameters ◽  
Normal Fault ◽  
Seismic Source ◽  
Vertical Gradient ◽  
Vertical Displacement ◽  
Source Inversion ◽  
Finite Source

Abstract. With the prospects of seismic equipment being able to measure rotational ground motions in a wide frequency and amplitude range in the near future, we engage in the question of how this type of ground motion observation can be used to solve the seismic source inverse problem. In this paper, we focus on the question of whether finite-source inversion can benefit from additional observations of rotational motion. Keeping the overall number of traces constant, we compare observations from a surface seismic network with 44 three-component translational sensors (classic seismometers) with those obtained with 22 six-component sensors (with additional three-component rotational motions). Synthetic seismograms are calculated for known finite-source properties. The corresponding inverse problem is posed in a probabilistic way using the Shannon information content to measure how the observations constrain the seismic source properties. We minimize the influence of the source receiver geometry around the fault by statistically analyzing six-component inversions with a random distribution of receivers. Since our previous results are achieved with a regular spacing of the receivers, we try to answer the question of whether the results are dependent on the spatial distribution of the receivers. The results show that with the six-component subnetworks, kinematic source inversions for source properties (such as rupture velocity, rise time, and slip amplitudes) are not only equally successful (even that would be beneficial because of the substantially reduced logistics installing half the sensors) but also statistically inversions for some source properties are almost always improved. This can be attributed to the fact that the (in particular vertical) gradient information is contained in the additional motion components. We compare these effects for strike-slip and normal-faulting type sources and confirm that the increase in inversion quality for kinematic source parameters is even higher for the normal fault. This indicates that the inversion benefits from the additional information provided by the horizontal rotation rates, i.e., information about the vertical displacement gradient.

scholarly journals Exploring the potentials and limitations of the time-reversal imaging of finite seismic sources

2011 ◽  
Vol 3 (1) ◽  
pp. 217-248 ◽  
Author(s):  
S. Kremers ◽  
A. Fichtner ◽  
G. B. Brietzke ◽  
H. Igel ◽  
C. Larmat ◽  
...  
Keyword(s):  
Frequency Band ◽  
Time Reversal ◽  
Standard Technique ◽  
Source Area ◽  
Rupture Process ◽  
Point Sources ◽  
Seismic Sources ◽  
Source Inversion ◽  
Origin Time ◽  
Finite Source

Abstract. The characterisation of seismic sources with time-reversed wave fields is developing into a standard technique that has already been successful in numerous applications. While the time-reversal imaging of effective point sources is now well-understood, little work has been done to extend this technique to the study of finite rupture processes. This is despite the pronounced non-uniqueness in classic finite source inversions. The need to better constrain the details of finite rupture processes motivates the series of synthetic and real-data time reversal experiments described in this paper. We address questions concerning the quality of focussing in the source area, the localisation of the fault plane, the estimation of the slip distribution and the source complexity up to which time-reversal imaging can be applied successfully. The frequency band for the synthetic experiments is chosen such that it is comparable to the band usually employed for finite source inversion. Contrary to our expectations, we find that time-reversal imaging is useful only for effective point sources, where it yields good estimates of both the source location and the origin time. In the case of finite sources, however, the time-reversed field does not provide meaningful characterisations of the fault location and the rupture process. This result cannot be improved sufficiently with the help of different imaging fields, realistic modifications of the receiver geometry or weights applied to the time-reversed sources. The reasons for this failure are manifold. They include the incomplete recording of wave field information at the surface, the excitation of large-amplitude surface waves that deteriorate the depth resolution, the absence of a sink that should absorb energy radiated during the later stages of the rupture process, the invisibility of small slip and the neglect of prior information concerning the fault geometry. The condensed conclusion of our study is that the limitations of time-reversal imaging – at least in the frequency band considered here – start where the seismic source stops being effectively point-localised.

Rupture parameters of dynamic source models compatible with NGA-West2 GMPEs

2020 ◽  
Author(s):  
Frantisek Gallovic ◽  
Lubica Valentova
Keyword(s):  
Ground Motions ◽  
Source Parameters ◽  
Strong Motion ◽  
Seismic Hazard Assessment ◽  
Response Spectra ◽  
Maximum Magnitude ◽  
Source Inversion ◽  
Dynamic Rupture ◽  
Heterogeneous Distribution ◽  
Dynamic Source

<p>Dynamic source inversions of individual earthquakes provide constraints on stress and frictional parameters, which are inherent to the studied event. However, general characteristics of both kinematic and dynamic rupture parameters are not well known, especially in terms of their variability. Here we constrain them by creating and analyzing a synthetic event database of dynamic rupture models that generate waveforms compatible with strong ground motions in a statistical sense.</p><p>We employ a framework that is similar to the Bayesian dynamic source inversion by Gallovič et al. (2019). Instead of waveforms of a single event, the data are represented by Ground Motion Prediction Equations (GMPEs), namely NGA-West2  (Boore et al., 2014). The Markov chain Monte Carlo technique produces samples of the dynamic source parameters with heterogeneous distribution on a fault. For all simulations, we assume a vertical 36x20km strike-slip fault, which limits our maximum magnitude to Mw<7. For dynamic rupture calculations, we employ upgraded finite-difference code FD3D_TSN (Premus et al., 2020) with linear slip-weakening friction law. Seismograms are calculated on a regular grid of phantom stations assuming a 1D velocity model using precalculated full wavefield Green's functions. The procedure results in a database with those dynamic rupture models that generate ground motions compatible with the GMPEs (acceleration response spectra in period band 0.5-5s) in terms of both median and variability.</p><p>The events exhibit various magnitudes and degrees of complexity (e.g. one or more asperities). We inspect seismologically determinable parameters, such as duration, moment rate spectrum, stress drop, size of the ruptured area, and energy budget, including their variabilities.  Comparison with empirically derived values and scaling relations suggests that the events are compatible with real earthquakes (Brune, 1970, Kanamori and Brodsky, 2004). Moreover, we investigate the stress and frictional parameters in terms of their scaling, power spectral densities, and possible correlations. The inferred statistical properties of the dynamic source parameters can be used for physics-based strong-motion modeling in seismic hazard assessment.</p>

A semi-empirical method for simulating strong ground motions based on variable-slip rupture models for large earthquakes

1999 ◽  
Vol 89 (1) ◽  
pp. 36-53
Author(s):  
Kazuo Dan ◽  
Toshiaki Sato
Keyword(s):  
Slip Velocity ◽  
Ground Motions ◽  
Seismic Intensity ◽  
Empirical Method ◽  
Source Inversion ◽  
Tokyo Metropolitan Area ◽  
Rupture Model ◽  
Semi Empirical ◽  
Large Earthquakes ◽  
Strong Ground

Abstract Variable-slip rupture models for large earthquakes, obtained by the source inversion of long-period (>4 sec) seismic waves, are taken into account in a semi-empirical method for simulating broadband (< about 10 sec) strong ground motions. The high-frequency (>0.25 Hz) source spectrum of the (p, q)th subfault is inferred by the θ−2 mode with two circular corner frequencies. The first is ωDpq = Vpq/Dpq, due to the temporal integration of the slip-velocity time function, where Vpq is the maximum slip velocity and Dpq is the final slip. The other is ωSpq = 2βpq/λpq, due to the spacial integration of the slip-velocity time function on the subfault, where βpq is the S-wave velocity of the medium and λpq is the equivalent radius of the subfault. Here, Vpq, Dpq, βpq, and λpq are specified by the long-period source-inversion results. First, we describe this new method by applying it to the variable-slip rupture model for the 1985 Michoacan, Mexico, earthquake of MS 8.1 obtained by Mendoza and Hartzell (1989). The simulated accelerations and velocities at CAL (Caleta de Campos) and VIL (La Villita), both located above the ruptured zone, are in good agreement with the observed ones. Next, the method is applied to the variable-slip rupture model for the 1923 Kanto, Japan, earthquake of MS 8.2 obtained by Wald and Somerville (1995). This earthquake is one of the most important earthquakes for the mitigation of earthquake disaster in the Tokyo metropolitan area; unfortunately, strong-motion records for this earthquake were off-scaled in the region of strong shaking and significant damage. The pseudo-velocity response spectrum of the simulated acceleration of TOK (Tokyo JMA) averages 60 cm/sec in the period range of 0.5 to 10 sec and is consistent with that of the Kanto earthquake record observed at HNG (Hongo, Tokyo), whose off-scaled parts were restored as well as possible by Yokota et al. (1989). The instrumental JMA seismic intensities (JMA, 1996) of the simulated accelerations at TOK and YOK (Yokohama JMA) are consistent with the observed JMA seismic intensity 6 (JMA, 1983). The instrumental JMA seismic intensity of the simulated accelerations at KNS (soil site in Odawara) is also consistent with the JMA seismic intensity 7, estimated from the ratio of collapsed houses (Mononobe, 1925). The simulated broadband (0.1 to 10 sec) motions will be useful in the mitigation of earthquake disaster in the Tokyo metropolitan area.

scholarly journals Exploring the potentials and limitations of the time-reversal imaging of finite seismic sources

Solid Earth ◽  
2011 ◽  
Vol 2 (1) ◽  
pp. 95-105 ◽  
Author(s):  
S. Kremers ◽  
A. Fichtner ◽  
G. B. Brietzke ◽  
H. Igel ◽  
C. Larmat ◽  
...  
Keyword(s):  
Frequency Band ◽  
Time Reversal ◽  
Standard Technique ◽  
Source Area ◽  
Rupture Process ◽  
Point Sources ◽  
Seismic Sources ◽  
Source Inversion ◽  
Origin Time ◽  
Finite Source

Abstract. The characterisation of seismic sources with time-reversed wave fields is developing into a standard technique that has already been successful in numerous applications. While the time-reversal imaging of effective point sources is now well-understood, little work has been done to extend this technique to the study of finite rupture processes. This is despite the pronounced non-uniqueness in classic finite source inversions. The need to better constrain the details of finite rupture processes motivates the series of synthetic and real-data time reversal experiments described in this paper. We address questions concerning the quality of focussing in the source area, the localisation of the fault plane, the estimation of the slip distribution and the source complexity up to which time-reversal imaging can be applied successfully. The frequency band for the synthetic experiments is chosen such that it is comparable to the band usually employed for finite source inversion. Contrary to our expectations, we find that time-reversal imaging is useful only for effective point sources, where it yields good estimates of both the source location and the origin time. In the case of finite sources, however, the time-reversed field does not provide meaningful characterisations of the fault location and the rupture process. This result cannot be improved sufficiently with the help of different imaging fields, realistic modifications of the receiver geometry or weights applied to the time-reversed sources. The reasons for this failure are manifold. They include the choice of the frequency band, the incomplete recording of wave field information at the surface, the excitation of large-amplitude surface waves that deteriorate the depth resolution, the absence of a sink that should absorb energy radiated during the later stages of the rupture process, the invisibility of small slip and the neglect of prior information concerning the fault geometry and the inherent smoothness of seismologically inferred Earth models that prevents the beneficial occurrence of strong multiple-scattering. The condensed conclusion of our study is that the limitations of time-reversal imaging – at least in the frequency band considered here – start where the seismic source stops being effectively point-localised.

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