scholarly journals Modeling the seismic cycle in subduction zones: The role and spatiotemporal occurrence of off-megathrust earthquakes

2014 ◽  
Vol 41 (4) ◽  
pp. 1194-1201 ◽  
Author(s):  
Y. van Dinther ◽  
P. M. Mai ◽  
L. A. Dalguer ◽  
T. V. Gerya
Keyword(s):  
Subduction Zones ◽  
Seismic Cycle ◽  
Megathrust Earthquakes

scholarly journals Keyboard Model of Seismic Cycle of Great Earthquakes in Subduction Zones: Simulation Results and Further Generalization

2021 ◽  
Vol 11 (19) ◽  
pp. 9350
Author(s):  
Leopold I. Lobkovsky ◽  
Irina S. Vladimirova ◽  
Yurii V. Gabsatarov ◽  
Dmitry A. Alekseev
Keyword(s):  
Subduction Zones ◽  
Specific Effect ◽  
Simulated Data ◽  
Tohoku Earthquake ◽  
Direct Analysis ◽  
Earthquake Forecasting ◽  
Seismic Cycle ◽  
Megathrust Earthquakes ◽  
Direct Interpretation ◽  
Maule Earthquake

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.

Proposed methodology for estimating the magnitude at which subduction megathrust ground motions and source dimensions exhibit a break in magnitude scaling: Example for 79 global subduction zones

2020 ◽  
Vol 36 (3) ◽  
pp. 1271-1297
Author(s):  
Kenneth W. Campbell
Keyword(s):  
Ground Motion ◽  
Subduction Zones ◽  
Ground Motions ◽  
Seismic Source ◽  
Scaling Relations ◽  
Megathrust Earthquakes ◽  
Source Dimensions ◽  
Magnitude Scaling ◽  
Aspect Ratios ◽  
Source Scaling

In this article, I propose a method for estimating the magnitude [Formula: see text] at which subduction megathrust earthquakes are expected to exhibit a break in magnitude scaling of both seismic source dimensions and earthquake ground motions. The methodology is demonstrated by applying it to 79 global subduction zones defined in the literature, including Cascadia. Breakpoint magnitude is estimated from seismogenic interface widths, empirical source scaling relations, and aspect ratios of physically unbounded earthquake ruptures and their uncertainties. The concept stems from the well-established observation that source-dimension and ground motion scaling decreases for shallow continental (primarily strike-slip) earthquakes when rupture exceeds the seismogenic width of the fault. Although a scaling break for megathrust earthquakes is difficult to observe empirically, all of the instrumentally recorded historical [Formula: see text] mega-earthquakes have occurred on subduction zones with [Formula: see text] (8.1–8.9), consistent with an observed break in source scaling relations derived from these same events. The breakpoint magnitudes derived in this study can be used to constrain the magnitude at which the scaling of ground motion is expected to decrease in subduction ground motion prediction equations.

Subduction zone heterogeneity observed across the magnitude spectrum for megathrust earthquakes

2021 ◽  
Author(s):  
Susan Bilek ◽  
Emily Morton
Keyword(s):  
Spatial Heterogeneity ◽  
Subduction Zone ◽  
Stress Drop ◽  
Subduction Zones ◽  
Cascadia Subduction Zone ◽  
Ocean Bottom ◽  
Small Earthquake ◽  
Megathrust Earthquakes ◽  
Seismic Slip ◽  
Subduction Zone Earthquakes

<p>Observations from recent great subduction zone earthquakes highlight the influence of spatial geologic heterogeneity on overall rupture characteristics, such as areas of high co-seismic slip, and resulting tsunami generation.  Defining the relevant spatial heterogeneity is thus important to understanding potential hazards associated with the megathrust. The more frequent, smaller magnitude earthquakes that commonly occur in subduction zones are often used to help delineate the spatial heterogeneity.  Here we provide an overview of several subduction zones, including Costa Rica, Mexico, and Cascadia, highlighting connections between the small earthquake source characteristics and rupture behavior of larger earthquakes.  Estimates of small earthquake locations and stress drop are presented in each location, utilizing data from coastal and/or ocean bottom seismic stations.  These seismicity characteristics are then compared with other geologic and geophysical parameters, such as upper and lower plate characteristics, geodetic locking, and asperity locations from past large earthquakes.  For example, in the Cascadia subduction zone, we find clusters of small earthquakes located in regions of previous seamount subduction, with variations in earthquake stress drop reflecting potentially disrupted upper plate material deformed as a seamount passed.  Other variations in earthquake location and stress drop can be correlated with observed geodetic locking variations. </p>

scholarly journals Predicting Imminence of Analog Megathrust Earthquakes With Machine Learning: Implications for Monitoring Subduction Zones

2020 ◽  
Vol 47 (7) ◽  
Author(s):  
F. Corbi ◽  
J. Bedford ◽  
L. Sandri ◽  
F. Funiciello ◽  
A. Gualandi ◽  
...  
Keyword(s):  
Machine Learning ◽  
Subduction Zones ◽  
Megathrust Earthquakes

scholarly journals New constraints on the 1922 Atacama, Chile, earthquake from Historical seismograms

2019 ◽  
Vol 219 (1) ◽  
pp. 645-661 ◽  
Author(s):  
Hiroo Kanamori ◽  
Luis Rivera ◽  
Lingling Ye ◽  
Thorne Lay ◽  
Satoko Murotani ◽  
...  
Keyword(s):  
Subduction Zones ◽  
Source Region ◽  
Plate Boundary ◽  
Spatial Proximity ◽  
Motion Data ◽  
Megathrust Earthquakes ◽  
Great Earthquakes ◽  
Chile Earthquake ◽  
Earthquake Research ◽  
Earthquake Research Institute

SUMMARY We recently found the original Omori seismograms recorded at Hongo, Tokyo, of the 1922 Atacama, Chile, earthquake (MS = 8.3) in the historical seismogram archive of the Earthquake Research Institute (ERI) of the University of Tokyo. These recordings enable a quantitative investigation of long-period seismic radiation from the 1922 earthquake. We document and provide interpretation of these seismograms together with a few other seismograms from Mizusawa, Japan, Uppsala, Sweden, Strasbourg, France, Zi-ka-wei, China and De Bilt, Netherlands. The 1922 event is of significant historical interest concerning the cause of tsunami, discovery of G wave, and study of various seismic phase and first-motion data. Also, because of its spatial proximity to the 1943, 1995 and 2015 great earthquakes in Chile, the 1922 event provides useful information on similarity and variability of great earthquakes on a subduction-zone boundary. The 1922 source region, having previously ruptured in 1796 and 1819, is considered to have significant seismic hazard. The focus of this paper is to document the 1922 seismograms so that they can be used for further seismological studies on global subduction zones. Since the instrument constants of the Omori seismographs were only incompletely documented, we estimate them using the waveforms of the observed records, a calibration pulse recorded on the seismogram and the waveforms of better calibrated Uppsala Wiechert seismograms. Comparison of the Hongo Omori seismograms with those of the 1995 Antofagasta, Chile, earthquake (Mw = 8.0) and the 2015 Illapel, Chile, earthquake (Mw = 8.3) suggests that the 1922 event is similar to the 1995 and 2015 events in mechanism (i.e. on the plate boundary megathrust) and rupture characteristics (i.e. not a tsunami earthquake) with Mw = 8.6 ± 0.25. However, the initial fine scale rupture process varies significantly from event to event. The G1 and G2, and R1 and R2 of the 1922 event are comparable in amplitude, suggesting a bilateral rupture, which is uncommon for large megathrust earthquakes.

On the cause of enhanced landward motion of the overriding plate after a major subduction earthquake

2020 ◽  
Author(s):  
Mario D'Acquisto ◽  
Matthew Herman ◽  
Rob Govers
Keyword(s):  
Subduction Zones ◽  
Relaxation Times ◽  
Underlying Mechanism ◽  
Rupture Zone ◽  
Elastic Response ◽  
Postseismic Deformation ◽  
Plate Interface ◽  
Mechanical Coupling ◽  
Megathrust Earthquakes ◽  
Viscous Relaxation

<div> <p>During and after a large megathrust earthquake, the overriding plate above the rupture zone moves oceanward. Enigmatically, the post-seismic motion of the overriding plate after several recent large earthquakes, further along strike from the rupture zone, was faster in the landward direction than before the event. Previous studies interpreted these changes as the result of increased mechanical coupling along the megathrust interface, transient slab acceleration, or bulk postseismic deformation with elastic bending mentioned as a possible underlying mechanism. Before invoking additional mechanisms, it is important to understand the contribution of postseismic deformation processes that are inherent features of megathrust earthquakes. We thus aim to quantify and analyse the deformation that produces landward motion during afterslip and viscous relaxation. </p> </div><div> <p>We use velocity-driven 3D mechanical finite element models, in which large megathrust earthquakes occur periodically on the finite plate interface. The model geometry is similar to most present-day subduction zones, but does not exactly match any specific subduction zone. </p> </div><div> <p>The results show increased post-seismic landward motion at (trench-parallel) distances greater than 450 km from the middle of the ruptured asperity. Similar patterns of landward motion are generated by viscous relaxation in the mantle wedge and by deep afterslip on the shear zone downdip of the brittle megathrust interface. Landward displacement due to postseismic relaxation largely accumulates at exponentially decaying rates until ~6 Maxwell relaxation times after the earthquake. The spatial distribution and magnitude of the velocity changes is broadly consistent with observations related to both the 2010 Maule and the 2011 Tohoku-oki earthquakes.  </p> </div><div> <p>Further model experiments show that patterns of landward motion due to afterslip and to viscous relaxation are insensitive to the locking pattern of the megathrust. However, the locking distribution does affect the magnitudes of the displacements and velocities. Results show that the increased landward displacement due to postseismic deformation scales directly proportionally to seismic moment. </p> </div><div> <p>We conclude that the landward motion results from in-plane horizontal bending of the overriding plate and mantle. This bending is an elastic response to oceanward tractions near the base of the plate around the ruptured asperity, causing extension locally and compression further away along-trench. This elastic in-plate bending consistently contributes to earthquake-associated changes in surface velocities for the biggest megathrust earthquakes, producing landward motion along strike from the rupture zone.</p> </div>

The Chile subduction zone : Nature of the lithosphere between alternating regions of slow earthquakes versus non slow earthquakes

2020 ◽  
Author(s):  
Pousali Mukherjee ◽  
Yoshihiro Ito ◽  
Emmanuel S. Garcia ◽  
Raymundo Plata-Martinez ◽  
Takuo Shibutani
Keyword(s):  
Subduction Zones ◽  
Receiver Function ◽  
Function Analysis ◽  
Fluid Distribution ◽  
Inversion Method ◽  
Megathrust Earthquakes ◽  
Slow Earthquake ◽  
Slow Earthquakes ◽  
Receiver Function Analysis ◽  
Earthquake Area

<p>Subduction zones host some of the greatest megathrust earthquakes in the world. Slow earthquakes have been discovered around the subduction zones of the Pacific rim very close to megathrust earthquakes. Investigating the lithosphere of the slow earthquake area versus non slow-earthquake area in subduction zones is crucial in understanding the role of the internal structure to control slow earthquakes. In this study, we investigate the lithospheric structure of stations in the slow earthquake area and non slow-earthquake areas in Chile using receiver function analysis and inversion method using teleseismic earthquakes. Here we focus on, especially the Vp/Vs ratios from both slow and non-slow earthquake areas, because the Vp/Vs ratio is sensitive to the fluid distribution in the lithosphere; the fluid distribution possibly controls the potential occurrence of slow earthquakes. Additionally, the nature of the slab can also play a crucial factor. The Vp/Vs ratio results across depth shows significantly higher value in the deeper oceanic slab region beneath the stations in the slow earthquake areas with higher contrast at the boundary.</p>

Relationships between deformation and morphology of forearc wedges and earthquake ruptures

2021 ◽  
Author(s):  
Nadaya Cubas
Keyword(s):  
Subduction Zones ◽  
Permanent Deformation ◽  
Seismic Cycle ◽  
Earthquake Rupture ◽  
Earthquake Ruptures ◽  
Mechanical Modelling ◽  
Seismic Behaviors ◽  
Deformation Patterns ◽  
Rupture Properties ◽  
Effective Friction

<p>Over the last decade, we have accumulated evidence that, along subduction zones, a significant part of the seismic cycle deformation is permanently acquired by the medium and reflects the variation of rupture properties along the megathrust. Assuming a persistence of the megathrust segmentation over several hundred thousand years, this permanent deformation and the forearc topography could thus reveal the mechanics of the megathrust. Numerous recent studies have also shown that the megathrust effective friction appears to differ significantly between aseismic or seismic areas. From mechanical modelling, I will first discuss how such differences in effective friction are significant enough to induce wedge segments with varying morphologies and deformation patterns. I will present examples from different subduction zones characterized by either erosive or accretionary wedges, and by different seismic behaviors. Secondly, I will present how this long-lived deformation can in turn control earthquake ruptures. I will show, that along the Chilean subduction zone, all recent mega-earthquakes are surrounded by basal erosion and underplating. Therefore, the deformation and morphology of forearcs would both be partly linked to the megathrust rupture properties and should be used in a more systematic manner to improve earthquake rupture prediction.</p>

Two-Element Keyboard-Block Model Of Megathrust Earthquakes Generation For Central Kurils

2021 ◽  
Author(s):  
Yurii Gabsatarov ◽  
Irina Vladimirova ◽  
Dmitry Alexeev ◽  
Leopold Lobkovsky
Keyword(s):  
Continental Margin ◽  
Block Structure ◽  
Continuous Model ◽  
Environmental Damage ◽  
Single Element ◽  
Seismic Cycle ◽  
Block Model ◽  
Megathrust Earthquakes ◽  
Fault Block ◽  
Rear Part

<p>The strongest subduction earthquakes (M≥8) lead to the release of the huge amount of elastic stresses accumulated over hundreds or even thousands of years. Prediction of such earthquakes, causing significant socio-economic and environmental damage, is one of the most important and urgent tasks of geophysics.</p><p>To date, significant advances have been made in the field of earthquake prediction using models based on the concept of a continuous geophysical medium that ruptured coseismically along the main fault. As an alternative, models are proposed that take into account the fault-block structure of the continental margin, confirmed by seismological and oceanographic studies. In our study, we consider one of such models - a keyboard-block model (single-element) which combines the ideas of possible synchronous destruction of several adjacent asperities, mutual slip along a plane with variable friction depending on velocity, and subsequent healing of destructed portions of the medium under high-pressure conditions. This concept made it possible to simulate the displacement of surface points of frontal seismogenic blocks at all stages of the seismic cycle.</p><p>GNSS observations in subduction regions are carried out mostly on islands situated on the rear massif far from the seismogenic blocks. Strong multidirectional motion registered on GNSS stations during the seismic cycle, as well as seismological and geological data, clearly indicate that the rear part of the arc also has a complex structure and is divided into separate segments by large faults rooted into the contact zone of interacting lithospheric plates. We made a generalization (double-element) of the original model to consider the discontinuity of not only the frontal but also the rear part of the island arc.</p><p>We compared the earth's surface displacements during the seismic cycle in the Central Kurils, obtained within the framework of the continuous model, as well as the single-element and two-element keyboard models, to establish the influence of various configurations of the fault-block structure of the continental margin on the seismic cycle. We constructed the continuous model on the basis of our slip distribution model for the 2006 Simushir earthquake which indicates the interplate coupling patches prior to this earthquake.</p><p>This study was supported by the Russian Science Foundation (project 20–17-00140).</p>

Modeling the Interaction between Slow Slip Events and Earthquake Ruptures in the Nicoya Peninsula, Costa Rica. 

2021 ◽  
Author(s):  
Lise Alalouf ◽  
Yajing Liu
Keyword(s):  
Costa Rica ◽  
Subduction Zones ◽  
Computation Time ◽  
Seismogenic Zone ◽  
Model Parameters ◽  
Slow Slip ◽  
Coseismic Slip ◽  
Slow Slip Events ◽  
Megathrust Earthquakes ◽  
Earthquake Ruptures

<p>Subduction zones are where the largest earthquakes occur. In the past few decades, scientists have also discovered the presence of episodic aseismic slip, including slow slip events (SSEs), along most of the subduction zones. However, it is still unclear how these SSEs can influence megathrust earthquake ruptures. The Costa Rica subduction zone is a particularly interesting area because a SSE was recorded 6 months before the 2012 Mw7.6 earthquake in the Nicoya Peninsula, suggesting a potential stress transfer from the SSE to the earthquake slip zone. SSEs beneath the Nicoya Peninsula were also recorded both updip and downdip the seismogenic zone, making it a unique area to study the complex interaction between SSEs and earthquakes.</p><p>As most of the shallow SSEs were recorded around the Nicoya Peninsula, we chose to start using a 1D planar fault embedded in a homogeneous elastic half-space, with different dipping angles following several geometric profiles of the subduction fault beneath the Nicoya Peninsula section of the Costa Rica margin. This 1D modelling study allows us to better investigate the interaction between shallow and deep SSEs and megathrust earthquakes with high numerical resolution and relatively short computation time. The model provides information on the long-term seismic history by reproducing the different stages of the seismic cycle (interseismic slip, shallow and deep episodic slow slip, and coseismic slip).</p><p>We study the influence of the variation of numerical parameters and frictional properties on the recurrence interval, maximum slip velocity and cumulative slip of SSEs (both shallow and deep) and earthquakes and their interaction with each other. We then compare our results with GPS and seismic observations (i.e. cumulative slip, characteristic duration, moment rate, depth and size of the rupture, equivalent magnitude) to identify an optimal set of model parameters to understand the interaction between various modes of subduction fault deformation.</p>

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