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.

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 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.

A teleseismic body-wave analysis of the May 1980 Mammoth Lakes, California, earthquakes

1983 ◽  
Vol 73 (2) ◽  
pp. 419-434
Author(s):  
Jeffery S. Barker ◽  
Charles A. Langston
Keyword(s):  
Body Wave ◽  
Moment Tensor ◽  
Normal Fault ◽  
Strike Slip ◽  
Body Waves ◽  
P Wave ◽  
Moment Tensors ◽  
Double Couple ◽  
The Moment ◽  
Mammoth Lakes

abstract Teleseismic P-wave first motions for the M ≧ 6 earthquakes near Mammoth Lakes, California, are inconsistent with the vertical strike-slip mechanisms determined from local and regional P-wave first motions. Combining these data sets allows three possible mechanisms: a north-striking, east-dipping strike-slip fault; a NE-striking oblique fault; and a NNW-striking normal fault. Inversion of long-period teleseismic P and SH waves for the events of 25 May 1980 (1633 UTC) and 27 May 1980 (1450 UTC) yields moment tensors with large non-double-couple components. The moment tensor for the first event may be decomposed into a major double couple with strike = 18°, dip = 61°, and rake = −15°, and a minor double couple with strike = 303°, dip = 43°, and rake = 224°. A similar decomposition for the last event yields strike = 25°, dip = 65°, rake = −6°, and strike = 312°, dip = 37°, and rake = 232°. Although the inversions were performed on only a few teleseismic body waves, the radiation patterns of the moment tensors are consistent with most of the P-wave first motion polarities at local, regional, and teleseismic distances. The stress axes inferred from the moment tensors are consistent with N65°E extension determined by geodetic measurements by Savage et al. (1981). Seismic moments computed from the moment tensors are 1.87 × 1025 dyne-cm for the 25 May 1980 (1633 UTC) event and 1.03 × 1025 dyne-cm for the 27 May 1980 (1450 UTC) event. The non-double-couple aspect of the moment tensors and the inability to obtain a convergent solution for the 25 May 1980 (1944 UTC) event may indicate that the assumptions of a point source and plane-layered structure implicit in the moment tensor inversion are not entirely valid for the Mammoth Lakes earthquakes.

scholarly journals The 2018 Mw 7.5 Palu Earthquake: A Supershear Rupture Event Constrained by InSAR and Broadband Regional Seismograms

2019 ◽  
Vol 11 (11) ◽  
pp. 1330 ◽  
Author(s):  
Jin Fang ◽  
Caijun Xu ◽  
Yangmao Wen ◽  
Shuai Wang ◽  
Guangyu Xu ◽  
...  
Keyword(s):  
Pulse Propagation ◽  
The South ◽  
The North ◽  
Strike Direction ◽  
Slip Pulse ◽  
Rupture Model ◽  
Dip Angle ◽  
Total Seismic Moment ◽  
The City ◽  
North And South

The 28 September 2018 Mw 7.5 Palu earthquake occurred at a triple junction zone where the Philippine Sea, Australian, and Sunda plates are convergent. Here, we utilized Advanced Land Observing Satellite-2 (ALOS-2) interferometry synthetic aperture radar (InSAR) data together with broadband regional seismograms to investigate the source geometry and rupture kinematics of this earthquake. Results showed that the 2018 Palu earthquake ruptured a fault plane with a relatively steep dip angle of ~85°. The preferred rupture model demonstrated that the earthquake was a supershear event from early on, with an average rupture speed of 4.1 km/s, which is different from the common supershear events that typically show an initial subshear rupture. The rupture expanded rapidly (~4.1 km/s) from the hypocenter and propagated bilaterally towards the north and south along the strike direction during the first 8 s, and then to the south. Four visible asperities were ruptured during the slip pulse propagation, which resulted in four significant deformation lobes in the coseismic interferogram. The maximum slip of 6.5 m was observed to the south of the city of Palu, and the total seismic moment released within 40 s was 2.64 × 1020 N·m, which was equivalent to Mw 7.55. Our results shed some light on the transtensional tectonism in Sulawesi, given that the 2018 Palu earthquake was dominated by left-lateral strike slip (slip maxima is 6.2 m) and that some significant normal faulting components (slip maxima is ~3 m) were resolved as well.

Rupture Kinematics of the 11 January 2021 Mw 6.7 Hovsgol, Mongolia, Earthquake and Implications in the Western Baikal Rift Zone

2021 ◽  
Author(s):  
Gang Liu ◽  
Xuejun Qiao ◽  
Pengfei Yu ◽  
Yu Zhou ◽  
Bin Zhao ◽  
...  
Keyword(s):  
Baikal Rift Zone ◽  
Tien Shan ◽  
Deformation Pattern ◽  
Convergence Region ◽  
The North ◽  
Finite Fault Inversion ◽  
Teleseismic Data ◽  
Finite Fault ◽  
The Right ◽  
Rupture Kinematics

Abstract The Mongolia plateau is the farthest intracontinental region of the India–Eurasia collision and is a transition zone between north–south convergence to the south in the Tien Shan and northwest–southeast extension to the north in the Baikal rift. Mongolia has experienced four M 8 earthquakes since 1905, but due to limited observations, the mechanism of these strong earthquakes and regional tectonics are poorly understood. The 11 January 2021 Mw 6.7 Hovsgol, Mongolia, earthquake is the largest event that has occurred in the Hovsgol graben, which is noted for being the northernmost convergence region of the India–Eurasia collision and the youngest extension region of the Baikal rift. In this article, the coseismic displacements are retrieved by space geodesy for the first time in this region, providing good constraints for the deformation pattern. We use a finite-fault inversion of InSAR and teleseismic data, and a backprojection analysis to reveal the rupture kinematics of this event. The geometry of the Hovsgol fault is determined as east-dipping with a dip of 45°. The rupture process is characterized by a northwestward propagation with a moderate average rupture velocity of ∼2.0  km/s and a complex slip pattern composed of two major slip patches with dimensions of 40  km×20  km. The oblique slip, illustrated by predominate extension and significant dextral striking, confirms the right-lateral-striking faulting in the Hovsgol rift, which indicates that the eastwardly north–south convergence across the southwest segment of the Baikal rift has decreased.

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.

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 The problems of the post-Cenomanian tectonic evolution of the central parts of the Sredna Gora Zone. The wrench tectonics – how real is real?

2020 ◽  
Vol 49 (2) ◽  
pp. 39-58
Author(s):  
Alexandre Kounov ◽  
Ianko Gerdjikov
Keyword(s):  
Shear Zone ◽  
Tectonic Evolution ◽  
Shear Zones ◽  
Strike Slip ◽  
Evidence Based ◽  
Strain Partitioning ◽  
Substantial Evidence ◽  
The North ◽  
Thrust Belts ◽  
The Moment

The Sredna Gora Zone holds a unique place in the tectonic subdivisions of the Balkanide orogen and its evolution is still a subject of debate. In the last twenty years, the idea of strike-slip-related evolution of the zone has been invoked. However, for the moment, the number of thorough studies where such a scenario is envisaged is limited, and substantial evidence based on detailed fieldwork is still missing. In this article, we discuss some of the major problems of the suggested wrench tectonic concept in the evolution of the central part of the Sredna Gora Zone. These are the character of some major shear zones in the area, to which strike-slip movements are attributed, and the transtension-transpression evolution scenario for the Chelopech and Panagyurishte basins. Despite refuting completely their wrench tectonic-related evolution, we confirm the presence of strike-slip and oblique slip structures cutting the sediments, whereas the time of their activity and role in the deformation of the basin fill are yet to be revealed. Finally, we present a model based on natural examples and analogue modeling, in which the long-lived dextral Maritsa shear zone represents a zone of localized strain partitioning, separating the opposite vergent thrust belts of the Rhodope to the south and the Sredna Gora and Balkan fold-thrust belt to the north, during oblique or possibly orthogonal convergence.

scholarly journals Slip distribution effect in spatial coulomb stress analysis (Case study: Palu earthquake on September 28, 2018)

2021 ◽  
Vol 873 (1) ◽  
pp. 012033
Author(s):  
Kevin Hanyu Clinton Wulur ◽  
Iman Suardi ◽  
Sesar Prabu Dwi Sriyanto ◽  
Yusuf Hadi Perdana
Keyword(s):  
Fault Plane ◽  
Body Wave ◽  
Slip Distribution ◽  
Inversion Method ◽  
Coulomb Stress ◽  
The North ◽  
Wave Inversion ◽  
Dip Angle ◽  
Coulomb Stress Analysis

Abstract On September 28, 2018, the Palu-Koro fault released the accumulated stress that caused the earthquake. An earthquake with magnitude 7.5 caused large and massive damage around Palu. There were many aftershocks along the Palu-Koro fault. This research aims to calculate a model of spatial Coulomb stress based on this event to find a correlation between mainshock and the aftershocks. The slip distribution was used as an input of the spatial stress Coulomb modeling to increase the accuracy. We use the Teleseismic Body-Wave Inversion method to calculate slip distribution along the fault plane. As a result, this earthquake was generated by the Palu-Koro fault movement with Mw 7.48, strike 350°, dip angle 67°, and rake -9°. There are three asperity zones along the fault plane located in the north and southern parts of the fault plane. The location of the most energy discharge is in the south asperity zone of the fault plane model with a maximum slip value of 1.65 meters. The spatial Coulomb stress change of this event shows that aftershocks concentration are in areas experiencing increased stress after the earthquake.

“HISTORICAL PRESENTATION” OR “LIBEL TO THE RACE”?: CENSORSHIP AND THE BIRTH OF A NATION

2015 ◽  
Vol 14 (4) ◽  
pp. 612-615
Author(s):  
Jennifer Fronc
Keyword(s):  
Civil War ◽  
Young Woman ◽  
Young Women ◽  
First Amendment ◽  
Motion Pictures ◽  
National Board ◽  
The North ◽  
Reconstruction Period ◽  
The Moment ◽  
North And South

On April 9, 1915, the fiftieth anniversary of General Lee's surrender at Appomattox, The Birth of a Nation opened in Boston. Audience members were “prepared for the unusual” the moment they entered the Tremont Theatre. After “a young man in evening dress and a silk hat” took tickets, “two young women in flounced hoop skirts and with long curls … ma[d]e a sort of graceful minuet bow, and hand[ed] you a program.” While “soldiers ‘on guard’ in the Civil War uniforms of the North and South” flanked the aisles, another costumed young woman “escort[ed] you to your seat.” As the film projector flickered to life, a title card issued an important caveat to the audience: “This is an historical presentation of the Civil War and Reconstruction period and is not meant to reflect in any way upon any race or people of today.” D. W. Griffith did not write this title card; rather, the National Board of Censorship of Motion Pictures (NBC) inserted it to fend off protestors and signal its commitment to filmmakers’ First Amendment rights.

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