megathrust earthquakes
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2022 ◽  
Author(s):  
Muhammad Taufiq Rafie ◽  
David P. Sahara ◽  
Phil R. Cummins ◽  
Wahyu Triyoso ◽  
Sri Widiyantoro

Abstract The seismically active Sumatra subduction zone has generated some of the largest earthquakes in the instrumental record, and both historical accounts and paleogeodetic coral studies indicate such activity has historical recorded megathrust earthquakes and transferred stress to the surrounding, including the Great Sumatran Fault (GSF). Therefore, evaluating the stress transfer from these large subduction earthquakes could delineate the highly stressed area as potential-earthquake region along the GSF. In this study, we investigated eight megathrust earthquakes from 1797 to 2010 and resolved the accumulated Coulomb stress changes onto the 18 segments along the GSF. Additionally, we also estimated the rate of tectonic stress on the GSF segments which experienced large earthquake using the case of: (1) no sliver movement and (2) with sliver movement. Based on the historical stress changes of large earthquakes and the increase in tectonic stress rate, we analysed the historical stress changes time evolution on the GSF. The Coulomb stress accumulation of megathrust earthquakes between 1797-1907 increase the stress changes mainly on the southern part of GSF which followed by four major events between 1890-1943. The estimation of tectonic stress rates using case (1) produces low rate and long recurrence intervals which implies that the megathrust earthquakes plays an important role in allowing the GSF earthquake to occur. When implementing the arc-parallel sliver movement of case (2) to the calculation, the tectonic stress rates is 9 to 58 times higher than case (1) of no sliver movement. The observed slip rate of 15-16 mm/yr at the GSF is consistent with the recurrence interval for full-segment rupture of 100-200 years obtained from case (2). This suggests that the GSF earthquake is more controlled by the rapid arc-parallel forearc sliver motion. Furthermore, the analysis of stress changes time evolution model shows that some segments such as Tripa (North and South), Angkola, Musi and Manna appear to be brought back in their seismic cycles since these segments have experienced full-segment rupture and likely locked, increasing their earthquake hazard potentials.


2021 ◽  
Vol 12 (1) ◽  
Author(s):  
Saeko Kita ◽  
Heidi Houston ◽  
Suguru Yabe ◽  
Sachiko Tanaka ◽  
Youichi Asano ◽  
...  

AbstractSlow slip phenomena deep in subduction zones reveal cyclic processes downdip of locked megathrusts. Here we analyze seismicity within a subducting oceanic slab, spanning ~50 major deep slow slip with tremor episodes over 17 years. Changes in rate, b-values, and stress orientations of in-slab seismicity are temporally associated with the episodes. Furthermore, although stress orientations in the slab below these slow slips may rotate slightly, in-slab orientations 20–50 km updip from there rotate farther, suggesting that previously-unrecognized transient slow slip occurs on the plate interface updip. We infer that fluid pressure propagates from slab to interface, promoting episodes of slow slip, which break mineral seals, allowing the pressure to propagate tens of km further updip along the interface where it promotes transient slow slips. The proposed methodology, based primarily on in-slab seismicity, may help monitor plate boundary conditions and slow slip phenomena, which can signal the beginning stages of megathrust earthquakes.


2021 ◽  
Vol 11 (23) ◽  
pp. 11310
Author(s):  
Muhammad Yudhi Rezaldi ◽  
Ambar Yoganingrum ◽  
Nuraini Rahma Hanifa ◽  
Yoshiyuki Kaneda ◽  
Siti Kania Kushadiani ◽  
...  

Three-dimensional (3D) modeling of tsunami events is intended to promote tsunami safety. However, the developed 3D modeling methods based on Computational Fluid Dynamics and photorealistic particle visualization have some weaknesses, such as not being similar to the original environment, not measuring the wave’s end point, and low image accuracy. The method for 3D modeling of tsunamis that results from this research can fulfil those weaknesses because it has advantages, such as being able to predict the end point of waves, similar to the original environment, and the height and area of inundation. In addition, the method produces more detailed and sharper spatial data. Modeling in this research is conducted using Agisoft Metashape Professional software to a produce 3D orthomosaic from pictures taken with Unmanned Aerial Vehicle (UAV) technique or drone (photogrammetry), and 3ds max software is used for wave simulation. We take a sample of an area in Cilacap, Indonesia that was impacted by the 2006 southwest coast tsunamis and may be vulnerable to future big megathrust earthquakes and tsunamis. The results could be used to provide several benefits, such as the creation of evacuation routes and the determination of appropriate locations for building shelters.


2021 ◽  
Author(s):  
◽  
Dee Ninis

<p>At the southern Hikurangi margin, the subduction interface between the Australian and Pacific plates, beneath the southern North Island of New Zealand, is ‘locked’. It has previously been estimated that sudden slip on this locked portion of the interface could result in a subduction zone or ‘megathrust’ earthquake of Mw 8.0-8.5 or larger. Historically, however, no significant (>Mw 7.2) subduction interface earthquake has occurred at the southern Hikurangi margin, and the hazard from subduction earthquakes to this region, which includes New Zealand’s capital city of Wellington, remains largely unknown.  Patterns of uplift at active margins can provide insight into subduction processes, including megathrust earthquakes. With the objectives to i) contribute to the understanding of partitioning of margin-parallel plate motion on to upper plate faults, and ii) provide insight into the relationship of permanent vertical deformation to subduction processes at the southern end of the Hikurangi margin, I investigate flights of late Pleistocene fluvial and marine terraces preserved across the lower North Island. Such geomorphic features, when constrained by numerical dating, provide a valuable set of data with which to quantify tectonic deformation - be they locally offset by a fault, or collectively uplifted across the margin.  Fault-offset fluvial terraces along the Hutt River, near Wellington, record dextral slip for the southern part of the Wellington Fault. From re-evaluated fault displacement measurements and new Optically Stimulated Luminescence (OSL) data, I estimate an average slip rate of 6.3 ± 1.9/1.2 mm/yr (2σ) during the last ~100 ka. However, slip on the Wellington Fault has not been steady throughout this time. During the Holocene, there was a phase of heightened ground rupture activity between ~8 and 10 ka, a period of relative quiescence between ~4.5 and 8 ka, and another period of heightened activity during the last ≤ 4.5 ka. Moreover, these results agree with independent paleoseismological evidence from other sites along the Wellington Fault for the timing of ground rupture events. The time-varying activity observed on the Wellington Fault may be regulated by stress interactions with other nearby upper plate active faults.  Net tectonic uplift of the southern Hikurangi margin is recorded by ancient emergent shore platforms preserved along the south coast of the North Island. I provide a new evaluation of the distribution and age of the Pleistocene marine terraces. Shore platform altitudes are accurately surveyed for the first time using Global Navigational Satellite Systems (GNSS). From these data I have determine the shore platform attitudes where they are preserved along the coast. The terraces are also dated, most for the first time, using OSL techniques. The most extensive Pleistocene terraces formed during Marine Isotope Stages (MIS) 5a, 5c, 5e and 7a. Because the ancient shorelines are now obscured by coverbed deposits, I use shore platform attitudes to reconstruct strandline elevations. These strandline elevations, corrected for sea level during their formative highstands, have been used to quantify rates of uplift across the southern Hikurangi margin.  In the forearc region of the Hikurangi margin, within ~70 km of the trough, uplift observed on the marine terraces along the Palliser Bay coast monotonically decreases away from the trough. The highest uplift rate of 1.7 ± 0.1 mm/yr is observed at the easternmost preserved terrace, near Cape Palliser, about 40 km from Hikurangi Trough. Further to the west, at Lake Ferry, uplift is 0.8 ± 0.1 mm/yr. The lowest rate of uplift, 0.2 ± 0.1 mm/yr, is observed at Wharekauhau, the westernmost marine terrace preserved on the Palliser Bay coast. Overall, the terraces are tilted towards the west, away from the trough, with older terraces exhibiting the most tilting. This long-wavelength pattern of uplift suggests that, in this forearc region of the margin, deep-seated processes, most likely subduction of a buoyant slab in combination with megathrust earthquakes, are the main contributors to permanent vertical deformation.  West of Palliser Bay, at a distance of >70 km from the Hikurangi Trough, vertical offsets on the marine terraces are evident across upper plate faults, most notably the Wairarapa and Ohariu Faults. The uplift rate at Baring Head, west and on the upthrown side of the Wairarapa Fault, is as much as 1.6 ± 0.1 mm/yr. At Tongue Point, where the Ohariu Fault offsets the marine terraces preserved there, uplift calculated from the western, upthrown side of the fault is 0.6 ± 0.1 mm/yr. These uplift rates suggest that, in the Axial Ranges, in addition to sediment underplating, movement on the major active upper plate faults also contributes to rock uplift.</p>


2021 ◽  
Author(s):  
◽  
Dee Ninis

<p>At the southern Hikurangi margin, the subduction interface between the Australian and Pacific plates, beneath the southern North Island of New Zealand, is ‘locked’. It has previously been estimated that sudden slip on this locked portion of the interface could result in a subduction zone or ‘megathrust’ earthquake of Mw 8.0-8.5 or larger. Historically, however, no significant (>Mw 7.2) subduction interface earthquake has occurred at the southern Hikurangi margin, and the hazard from subduction earthquakes to this region, which includes New Zealand’s capital city of Wellington, remains largely unknown.  Patterns of uplift at active margins can provide insight into subduction processes, including megathrust earthquakes. With the objectives to i) contribute to the understanding of partitioning of margin-parallel plate motion on to upper plate faults, and ii) provide insight into the relationship of permanent vertical deformation to subduction processes at the southern end of the Hikurangi margin, I investigate flights of late Pleistocene fluvial and marine terraces preserved across the lower North Island. Such geomorphic features, when constrained by numerical dating, provide a valuable set of data with which to quantify tectonic deformation - be they locally offset by a fault, or collectively uplifted across the margin.  Fault-offset fluvial terraces along the Hutt River, near Wellington, record dextral slip for the southern part of the Wellington Fault. From re-evaluated fault displacement measurements and new Optically Stimulated Luminescence (OSL) data, I estimate an average slip rate of 6.3 ± 1.9/1.2 mm/yr (2σ) during the last ~100 ka. However, slip on the Wellington Fault has not been steady throughout this time. During the Holocene, there was a phase of heightened ground rupture activity between ~8 and 10 ka, a period of relative quiescence between ~4.5 and 8 ka, and another period of heightened activity during the last ≤ 4.5 ka. Moreover, these results agree with independent paleoseismological evidence from other sites along the Wellington Fault for the timing of ground rupture events. The time-varying activity observed on the Wellington Fault may be regulated by stress interactions with other nearby upper plate active faults.  Net tectonic uplift of the southern Hikurangi margin is recorded by ancient emergent shore platforms preserved along the south coast of the North Island. I provide a new evaluation of the distribution and age of the Pleistocene marine terraces. Shore platform altitudes are accurately surveyed for the first time using Global Navigational Satellite Systems (GNSS). From these data I have determine the shore platform attitudes where they are preserved along the coast. The terraces are also dated, most for the first time, using OSL techniques. The most extensive Pleistocene terraces formed during Marine Isotope Stages (MIS) 5a, 5c, 5e and 7a. Because the ancient shorelines are now obscured by coverbed deposits, I use shore platform attitudes to reconstruct strandline elevations. These strandline elevations, corrected for sea level during their formative highstands, have been used to quantify rates of uplift across the southern Hikurangi margin.  In the forearc region of the Hikurangi margin, within ~70 km of the trough, uplift observed on the marine terraces along the Palliser Bay coast monotonically decreases away from the trough. The highest uplift rate of 1.7 ± 0.1 mm/yr is observed at the easternmost preserved terrace, near Cape Palliser, about 40 km from Hikurangi Trough. Further to the west, at Lake Ferry, uplift is 0.8 ± 0.1 mm/yr. The lowest rate of uplift, 0.2 ± 0.1 mm/yr, is observed at Wharekauhau, the westernmost marine terrace preserved on the Palliser Bay coast. Overall, the terraces are tilted towards the west, away from the trough, with older terraces exhibiting the most tilting. This long-wavelength pattern of uplift suggests that, in this forearc region of the margin, deep-seated processes, most likely subduction of a buoyant slab in combination with megathrust earthquakes, are the main contributors to permanent vertical deformation.  West of Palliser Bay, at a distance of >70 km from the Hikurangi Trough, vertical offsets on the marine terraces are evident across upper plate faults, most notably the Wairarapa and Ohariu Faults. The uplift rate at Baring Head, west and on the upthrown side of the Wairarapa Fault, is as much as 1.6 ± 0.1 mm/yr. At Tongue Point, where the Ohariu Fault offsets the marine terraces preserved there, uplift calculated from the western, upthrown side of the fault is 0.6 ± 0.1 mm/yr. These uplift rates suggest that, in the Axial Ranges, in addition to sediment underplating, movement on the major active upper plate faults also contributes to rock uplift.</p>


Author(s):  
Francisco Acuña ◽  
Gonzalo A. Montalva ◽  
Daniel Melnick

Abstract Time-dependent earthquake forecast depends on the frequency and number of past events and time since the last event. Unfortunately, only a few past events are historically documented along subduction zones where forecasting relies mostly on paleoseismic catalogs. We address the role of dating uncertainty and completeness of paleoseismic catalogs on probabilistic estimates of forthcoming earthquakes using a 3.6-ka-long catalog including 11 paleoseismic and 1 historic (Mw≥8.6) earthquakes that preceded the great 1960 Chile earthquake. We set the clock to 1940 and estimate the conditional probability of a future event using five different recurrence models. We find that the Weibull model predicts the highest forecasting probabilities of 44% and 72% in the next 50 and 100 yr, respectively. Uncertainties in earthquake chronologies due to missing events and dating uncertainties may produce changes in forecast probabilities of up to 50%. Our study provides a framework to use paleoseismic records in seismic hazard assessments including epistemic uncertainties.


2021 ◽  
Vol 73 (1) ◽  
Author(s):  
Masayuki Kano ◽  
Aoi Ikeuchi ◽  
Takuya Nishimura ◽  
Shin’ichi Miyazaki ◽  
Takeshi Matsushima

AbstractThe southern part of the Ryukyu subduction zone has recorded tsunami events with a recurrence interval of several hundred years. Although their source is controversial, one model suggests that the last 1771 Yaeyama tsunami was caused by a shallow megathrust earthquake with a magnitude of 8. However, the current knowledge on interplate coupling based on recent geodetic data is limited. Here, a time series of Global Navigation Satellite System data from January 2010 to February 2021 was analyzed, including newly installed stations by Kyoto and Kyushu Universities, to obtain the distance changes between stations and vertical secular velocities. The distance changes ranged from 2.4 mm/year in contraction and to 4.7 mm/year in extension, and the vertical velocities exhibited no clear uplift or subsidence, with − 2.4 to 1.1 mm/year. The back slip inversion results indicated a slip deficit of 17–47 mm/year to the south of the Yaeyama Islands. The large slip deficit area is complementarily intervened between the shallower source area of low-frequency earthquakes and the deeper slow slip region, suggesting the spatial heterogeneity of frictional properties along the plate interface. If the large slip deficit area accumulates stress in the same rate since the last 1771 earthquake, it could result in a megathrust event with a moment magnitude greater than 7.5. Because the limited onshore data cannot resolve the slip deficit on the shallow plate interface, seafloor geodetic observations are essential to clarify the detailed spatial distribution of the slip deficit and discuss its earthquake and tsunami potential. Graphical Abstract


2021 ◽  
Vol 11 (19) ◽  
pp. 9350
Author(s):  
Leopold I. Lobkovsky ◽  
Irina S. Vladimirova ◽  
Yurii V. Gabsatarov ◽  
Dmitry A. Alekseev

Catastrophic megaearthquakes (M > 8) occurring in the subduction zones are among the most devastating hazards on the planet. In this paper we discuss the seismic cycles of the megathrust earthquakes and propose a blockwise geomechanical model explaining certain features of the stress-deformation cycle revealed in recent decades from seismological and satellite geodesy (GNSS) observations. Starting with an overview of the so-called keyboard model of the seismic cycle by L. Lobkovsky, we outline mathematical formalism describing the motion of seismogenic block system assuming viscous rheology beneath and between the neighboring elastic blocks sitting on top of the subducting slab. By summarizing the GNSS-based evidence from our previous studies concerning the transient motions associated with the 2006–2007 Simushir earthquakes, 2010 Maule earthquake, and 2011 Tohoku earthquake, we demonstrate that those data support the keyboard model and reveal specific effect of the postseismic oceanward motion. However, since the seismogenic blocks in subduction systems are mostly located offshore, the direct analysis of GNSS-measured displacements and velocities is hardly possible in terms of the original keyboard model. Hence, the generalized two-segment keyboard model is introduced, containing both frontal offshore blocks and rear onshore blocks, which allows for direct interpretation of the onshore-collected GNSS data. We present a numerical computation scheme and a series of simulated data, which exhibits the consistency with measured motions and enables estimating the seismic cycle characteristics, important for the long-term earthquake forecasting.


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