scholarly journals Construction of fault geometry by finite-fault inversion of teleseismic data

2020 ◽  
Vol 224 (2) ◽  
pp. 1003-1014
Author(s):  
Kousuke Shimizu ◽  
Yuji Yagi ◽  
Ryo Okuwaki ◽  
Yukitoshi Fukahata
Keyword(s):  
Fault Plane ◽  
Seismic Source ◽  
Rupture Process ◽  
Inversion Method ◽  
Source Inversion ◽  
Fault Geometry ◽  
Waveform Data ◽  
Finite Fault Inversion ◽  
Finite Fault ◽  
Double Couple

SUMMARY Conventional seismic source inversion estimates the earthquake rupture process on an assumed fault plane that is determined a priori. It has been a difficult challenge to obtain the fault geometry together with the rupture process by seismic source inversion because of the nonlinearity of the inversion technique. In this study, we propose an inversion method to estimate the fault geometry and the rupture process of an earthquake from teleseismic P waveform data, through an elaboration of our previously published finite-fault inversion analysis (Shimizu et al. 2020). That method differs from conventional methods by representing slip on a fault plane with five basis double-couple components, expressed by potency density tensors, instead of two double-couple components compatible with the fault direction. Because the slip direction obtained from the potency density tensors should be compatible with the fault direction, we can obtain the fault geometry consistent with the rupture process. In practice we rely on an iterative process, first assuming a flat fault plane and then updating the fault geometry by using the information included in the obtained potency density tensors. In constructing a non-planar model-fault surface, we assume for simplicity that the fault direction changes only in either the strike or the dip direction. After checking the validity of the proposed method through synthetic tests, we applied it to the MW 7.7 2013 Balochistan, Pakistan, and MW 7.9 2015 Gorkha, Nepal, earthquakes, which occurred along geometrically complex fault systems. The modelled fault for the Balochistan earthquake is a curved strike-slip fault convex to the south-east, which is consistent with the observed surface ruptures. The modelled fault for the Gorkha earthquake is a reverse fault with a ramp-flat-ramp structure, which is also consistent with the fault geometry derived from geodetic and geological data. These results exhibit that the proposed method works well for constraining fault geometry of an earthquake.

scholarly journals Consecutive ruptures on a complex conjugate fault system during the 2018 Gulf of Alaska earthquake

2021 ◽  
Vol 11 (1) ◽  
Author(s):  
Shinji Yamashita ◽  
Yuji Yagi ◽  
Ryo Okuwaki ◽  
Kousuke Shimizu ◽  
Ryoichiro Agata ◽  
...  
Keyword(s):  
Gulf Of Alaska ◽  
Source Model ◽  
Fault System ◽  
Complex Conjugate ◽  
Inversion Method ◽  
Fault Geometry ◽  
Conjugate System ◽  
Finite Fault Inversion ◽  
Finite Fault ◽  
Alaska Earthquake

AbstractWe developed a flexible finite-fault inversion method for teleseismic P waveforms to obtain a detailed rupture process of a complex multiple-fault earthquake. We estimate the distribution of potency-rate density tensors on an assumed model plane to clarify rupture evolution processes, including variations of fault geometry. We applied our method to the 23 January 2018 Gulf of Alaska earthquake by representing slip on a projected horizontal model plane at a depth of 33.6 km to fit the distribution of aftershocks occurring within one week of the mainshock. The obtained source model, which successfully explained the complex teleseismic P waveforms, shows that the 2018 earthquake ruptured a conjugate system of N-S and E-W faults. The spatiotemporal rupture evolution indicates irregular rupture behavior involving a multiple-shock sequence, which is likely associated with discontinuities in the fault geometry that originated from E-W sea-floor fracture zones and N-S plate-bending faults.

scholarly journals Development of an inversion method to extract information on fault geometry from teleseismic data

2019 ◽  
Vol 220 (2) ◽  
pp. 1055-1065 ◽  
Author(s):  
Kousuke Shimizu ◽  
Yuji Yagi ◽  
Ryo Okuwaki ◽  
Yukitoshi Fukahata
Keyword(s):  
Fault Plane ◽  
Slip Rate ◽  
Rate Function ◽  
Fault Slip ◽  
Body Waves ◽  
Fault System ◽  
Inversion Method ◽  
Fault Geometry ◽  
Finite Fault ◽  
Extract Information

SUMMARY Teleseismic waveforms contain information on fault slip evolution during an earthquake, as well as on the fault geometry. A linear finite-fault inversion method is a tool for solving the slip-rate function distribution under an assumption of fault geometry as a single or multiple-fault-plane model. An inappropriate assumption of fault geometry would tend to distort the solution due to Green’s function modelling errors. We developed a new inversion method to extract information on fault geometry along with the slip-rate function from observed teleseismic waveforms. In this method, as in most previous studies, we assumed a flat fault plane, but we allowed arbitrary directions of slip not necessarily parallel to the assumed fault plane. More precisely, the method represents fault slip on the assumed fault by the superposition of five basis components of potency-density tensor, which can express arbitrary fault slip that occurs underground. We tested the developed method by applying it to real teleseismic P waveforms of the MW 7.7 2013 Balochistan, Pakistan, earthquake, which is thought to have occurred along a curved fault system. The obtained spatiotemporal distribution of potency-density tensors showed that the focal mechanism at each source knot was dominated by a strike-slip component with successive strike angle rotation from 205° to 240° as the rupture propagated unilaterally towards the south-west from the epicentre. This result is consistent with Earth’s surface deformation observed in optical satellite images. The success of the developed method is attributable to the fact that teleseismic body waves are not very sensitive to the spatial location of fault slip, whereas they are very sensitive to the direction of fault slip. The method may be a powerful tool to extract information on fault geometry along with the slip-rate function without requiring detailed assumptions about fault geometry.

scholarly journals Complex rupture process of the 2014 Thailand Mw 6.2 earthquake on the conjugate fault system of the Phayao fault zone

2021 ◽  
Author(s):  
Tira Tadapansawut ◽  
Yagi Yuji ◽  
Ryo Okuwaki ◽  
Shinji Yamashita ◽  
Kousuke Shimizu
Keyword(s):  
Fault Zone ◽  
Fault Plane ◽  
Rupture Process ◽  
Fault System ◽  
Small Scale ◽  
Fault Geometry ◽  
Geological Setting ◽  
Complex Fault ◽  
Finite Fault ◽  
Complex Fault System

The earthquake with a moment magnitude 6.2 that occurred in northern Thailand on 5 May 2014 is the largest recorded in Thailand by modern seismographs; the source is located in the multi-segmented complex fault system of the Phayao fault zone in the northern Thai province of Chiang Rai. This geological setting is appropriate environment for investigating a compound rupture process associated with a geometrically complex fault system in a magnitude-6-class earthquake. To understand in detail the rupture process of the 2014 Thailand earthquake, we elaborate the flexible finite-fault inversion method, used it to invert the globally-observed teleseismic P waveforms, and resolved for the spatiotemporal distribution of both the slip and the fault geometry. The complex rupture process consists of two distinct coseismic slip episodes that evolved along two discontinuous fault planes; these planes coincide with the lineations of the aftershock distribution. The first episode originated at the hypocenter and the rupture propagated south along the north-northeast to south-southwest fault plane. The second episode was triggered at around 5 km north from the epicenter and the rupture propagated along the east-northeast to west-southwest fault plane and terminated at the west end of the source area at 4.5 s hypocentral time. The fault system derived from our finite-fault model suggests geometric complexities including bends. The derived spatiotemporal orientation of the principal stress axis shows different lineations within the two rupture areas and heterogeneity at their edges. This geological setting may have caused the perturbation of the rupture propagation and the triggering of the distinct rupture episodes. Our source model of the 2014 Thailand earthquake suggests that even in the case of small-scale earthquakes, the rupture evolution can be complex when the underlying fault geometry is multiplex.

Source inversion of the 1988 Upland, California, earthquake: Determination of a fault plane for a small event

1990 ◽  
Vol 80 (3) ◽  
pp. 507-518 ◽  
Author(s):  
Jim Mori ◽  
Stephen Hartzell
Keyword(s):  
Green Function ◽  
Fault Plane ◽  
Least Squares Method ◽  
Source Area ◽  
Rupture Velocity ◽  
P Waves ◽  
Waveform Data ◽  
Empirical Green Function ◽  
Finite Fault ◽  
Short Period

Abstract We examined short-period P waves to investigate if waveform data could be used to determine which of two nodal planes was the actual fault plane for a small (ML 4.6) earthquake near Upland, California. We removed path and site complications by choosing a small aftershock (ML 2.7) as an empirical Green function. The main shock P waves were deconvolved by using the empirical Green function to produce simple far-field displacement pulses. We used a least-squares method to invert these pulses for the slip distribution on a finite fault. Both nodal planes (strike 125°, dip 85° and strike 221°, dip 40°) of the first-motion focal mechanism were tested at various rupture velocities. The southwest trending fault plane consistently gave better fitting solutions than the southeast-trending plane. We determined a moment of 4.2 × 1022 dyne-cm. The rupture velocity, and thus the source area could not be well resolved, but if we assume a reasonable rupture velocity of 0.87 times the shear wave velocity, we obtain a source area of 0.97 km2 and a stress drop of 38 bars. Choice of a southwest-trending fault plane is consistent with the trend of the nearby portion of the Transverse Ranges frontal fault zone and indicates left-lateral motion. This method provides a way to determine the fault plane for small earthquakes that have no surface rupture and no obvious trend in aftershock locations.

scholarly journals THE 2014 MW 6.9 NORTH AEGEAN TROUGH (NAT) EARTHQUAKE: SEISMOLOGICAL AND GEODETIC EVIDENCE

2017 ◽  
Vol 50 (3) ◽  
pp. 1583
Author(s):  
V. Saltogianni ◽  
M. Gianniou ◽  
T. Taymaz ◽  
S. Yolsal-Çevikbilen ◽  
S. Stiros
Keyword(s):  
Broad Band ◽  
Strike Slip ◽  
Fault Geometry ◽  
Coseismic Slip ◽  
The North ◽  
Finite Fault Inversion ◽  
Seismological Data ◽  
Finite Fault ◽  
Slip History ◽  
North Aegean

A strong earthquake (Mw 6.9) on 24 May 2014 ruptured the North Aegean Trough (NAT) in Greece, west of the North Anatolian Fault Zone (NAFZ). In order to provide unbiased constrains of the rupture process and fault geometry of the earthquake, seismological and geodetic data were analyzed independently. First, based on teleseismic long-period P- and SH- waveforms a point-source solution yielded dominantly right-lateral strike-slip faulting mechanism. Furthermore, finite fault inversion of broad-band data revealed the slip history of the earthquake. Second, GPS slip vectors derived from 11 permanent GPS stations uniformly distributed around the meizoseismal area of the earthquake indicated significant horizontal coseismic slip. Inversion of GPS-derived displacements on the basis of Okada model and using the new TOPological INVersion (TOPINV) algorithm permitted to model a vertical strike slip fault, consistent with that derived from seismological data. Obtained results are consistent with the NAT structure and constrain well the fault geometry and the dynamics of the 2014 earthquake. The latter seems to fill a gap in seismicity along the NAT in the last 50 years, but seems not to have a direct relationship with the sequence of recent faulting farther east, along the NAFZ.

scholarly journals Construction of fault geometry by finite-fault inversion of teleseismic data

2020 ◽  
Author(s):  
Kousuke Shimizu ◽  
Yuji Yagi ◽  
Ryo Okuwaki ◽  
Yukitoshi Fukahata
Keyword(s):  
Fault Geometry ◽  
Finite Fault Inversion ◽  
Teleseismic Data ◽  
Finite Fault

Imaging the rupture process of recent earthquakes using backprojection of local high frequency records

2020 ◽  
Author(s):  
Ioannis Fountoulakis ◽  
Christos Evangelidis ◽  
Olga-Joan Ktenidou
Keyword(s):  
High Frequency ◽  
A Priori ◽  
Strong Motion ◽  
Seismic Hazard Assessment ◽  
Seismic Source ◽  
Site Effect ◽  
Source Inversion ◽  
Waveform Data ◽  
Novel Approach ◽  
Spatio Temporal

<p>The seismic source spatio-temporal rupture processes of events in Japan, Greece and Turkey are imaged by backprojection of strong-motion waveforms. Normalized high-frequency (> 2Hz) S-waveforms from recordings on dense strong-motion networks are used to scan a predefined 3D source volume over time. </p><p>Backprojection is an alternative novel approach to image the spatio-temporal earthquake rupture. The method was first applied for large earthquakes at teleseismic distances, but is nowadays also used at local distances and over higher frequencies. The greatest advantage of the method is that processing is done without any a-priori constraints on the geometry, or size of the source. Thus, the spatio-temporal imaging of the rupture is feasible at higher frequencies (> 1Hz) than conventional source inversion studies, even when the examined fault geometry is complex. This high-frequency energy emitted during an earthquake is of great importance in seismic hazard assessment for certain critical infrastructures. The actual challenge in using high-frequency local recordings is to distinguish the local site effects from the true earthquake source content - otherwise, mapping the former incorrectly onto the latter limits the resolvability of the method. It is not straightforward to remove the site effect component or even to distinguish good reference stations from amid hard-soil and rock sites. In this study, the advantages and limitations of the method are explored using waveform data from well-recorded events in Japan (Kumamoto Mw7.1, 2016), Turkey (Marmara Mw6.4, 2019) and Greece (Antikythera Mw6.1, 2019). For each event and seismic array the resolution limits of the applied method are explored by performing various synthetic tests.</p>

A user-friendly probabilistic earthquake source inversion framework for joint inversion of seismic, geodetic, and gravitational signals - The Grond toolkit

2020 ◽  
Author(s):  
Sebastian Heimann ◽  
Marius Isken ◽  
Daniela Kühn ◽  
Hannes Vasyura-Bathke ◽  
Henriette Sudhaus ◽  
...  
Keyword(s):  
Open Source ◽  
Joint Inversion ◽  
Moment Tensor ◽  
Source Parameters ◽  
Seismic Source ◽  
Magma Ascent ◽  
Caldera Collapse ◽  
Waveform Data ◽  
Trade Offs ◽  
Finite Fault

<p>Seismic source and moment tensor waveform inversion is often ill-posed or non-unique if station coverage is poor or signals are weak. Three key ingredients can help in these situations: (1) probabilistic inference and global search of the full model space, (2) joint optimisation with datasets yielding complementary information, and (3) robust source parameterisation or additional source constraints. These demands lead to vast technical challenges, on the performance of forward modelling, on the optimisation algorithms, as well as on visualisation, optimisation configuration, and management of the datasets. Implementing a high amount of automation is inevitable.</p><p>To tackle all these challenges, we are developing a sophisticated new seismic source optimisation framework, Grond. With its innovative Bayesian bootstrap optimiser, it is able to efficiently explore large model spaces, the trade-offs and the uncertainties of source parameters. The program is highly flexible with respect to the adaption to specific source problems, the design of objective functions, and the diversity of empirical datasets.</p><p>It uses an integrated, robust waveform data processing, and allows for interactive visual inspection of many aspects of the optimisation problem, including visualisation of the result uncertainties. Grond has been applied to CMT moment tensor and finite-fault optimisations at all scales, to nuclear explosions, to a meteorite atmospheric explosion, and to volcano-tectonic processes during caldera collapse and magma ascent. Hundreds of seismic events can be handled in parallel given a single optimisation setup.</p><p>Grond can be used to optimise simultaneously seismic waveforms, amplitude spectra, waveform features, phase picks, static displacements from InSAR and GNSS, and gravitational signals.</p><p>Grond is developed as an open-source package and community effort. It builds on and integrates with other established open-source packages, like Kite (for InSAR) and Pyrocko (for seismology).</p>

3-D joint geodetic and strong-motion finite fault inversion of the 2008 May 12, Wenchuan, China Earthquake

2020 ◽  
Vol 222 (2) ◽  
pp. 1390-1404
Author(s):  
Leonardo Ramirez-Guzman ◽  
Stephen Hartzell
Keyword(s):  
Time Window ◽  
Joint Inversion ◽  
Strong Motion ◽  
Multiple Time ◽  
Source Inversion ◽  
Geodetic Inversion ◽  
Finite Fault Inversion ◽  
Finite Fault ◽  
China Earthquake ◽  
The Moment

SUMMARY We present a source inversion of the 2008 Wenchuan, China earthquake, using strong-motion waveforms and geodetic offsets together with 3-D synthetic ground motions. We applied the linear multiple time window technique considering geodetic and dynamic Green's functions computed with the finite-element method and the reciprocity and Strain Green's Tensor formalism. All ground motion estimates, valid up to 1 Hz, accounted for 3-D effects, including the topography and the geometry of the Beichuan and Pengguan faults. Our joint inversion has a higher moment (M0) than a purely geodetic inversion and the slip distribution presents differences when compared to 1-D model source inversions. The moment is estimated to be M0 = 1.2 × 1021 N·m, slightly larger than other works. Our results show that considering a complex 3-D structure reduces the size of large areas of 10 m slip or greater by distributing it in wider zones, with reduced slips, in the central portion of the Beichuan and the Pengguan faults. Finally, we compare our source with a relocated aftershock catalogue and conclude that the 4–5 m slip contours approximately bound the absence or presence of aftershocks.

Two main rupture stages during the 2018 magnitude 7.5 Sulawesi earthquake

2020 ◽  
Vol 221 (3) ◽  
pp. 1873-1882
Author(s):  
Qi Li ◽  
Bin Zhao ◽  
Kai Tan ◽  
Wenbin Xu
Keyword(s):  
Body Wave ◽  
Geographical Location ◽  
Strike Slip ◽  
Inversion Method ◽  
The North ◽  
Finite Fault Inversion ◽  
Strike Direction ◽  
Finite Fault ◽  
The Moment ◽  
North And South

SUMMARY On 28 September 2018, a Mw 7.5 strike-slip earthquake occurred in Sulawesi Island, Indonesia, and it unexpectedly triggered a tsunami. To clearly understand the spatiotemporal evolution process of source rupture, we collected the far-field body wave data and utilized the back-projection method together with finite fault inversion method to investigate the rupture kinematics of this earthquake. Results obtained with the two methods have good consistency and complementarity. We hold that the rupture expanded from the epicentre and propagated bilaterally towards the north and south along the strike direction during the first 24 s, and then to the south. Therefore, the whole rupture process consists of two main stages. For the second stage, the fault segment experienced most of the moment release between 0 and 15 km depth, while the fault plane tended to slip at greater depth (down to 20 km) in the first stage. The total length of the rupture was about 200 km and the seismic moment was ∼2.48 × 1020 Nm, which was equivalent to Mw 7.5. The surface rupture was evident and the maximum slip of 6.24 m was observed in the Palu basin, which was close to Palu city. The rupture was dominated by left-lateral strike-slip with both normal and thrust components as well. The normal slip exhibited in the shallow part of the fault on the north side of Palu bay together with the special geographical location of Palu bay likely favored tsunami genesis.

Sign in / Sign up

Export Citation Format

Share Document