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

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.

Download Full-text

Inferring seismic hazards from a new 1:25,000 scale map of active and potentially-active continental faults in Chile

10.5194/egusphere-egu2020-10399 ◽

2020 ◽

Author(s):

Daniel Melnick ◽

Valentina Maldonado ◽

Martin Contreras ◽

Julius Jara-Muñoz ◽

Joaquín Cortés-Aranda ◽

...

Keyword(s):

Subduction Zones ◽

National Level ◽

Active Faults ◽

Slip Rate ◽

Stress Transfer ◽

Field Studies ◽

Seismic Hazards ◽

Slip Rates ◽

Megathrust Earthquakes ◽

Maule Earthquake

Most of the seismic hazard along subduction zones is posed by great tsunamigenic earthquakes associated with the interplate megathrust fault. However, crustal faults are ubiquitous along overriding continental plates, some of which have been triggered during recent megathrust earthquakes. In Chile, the 2010 Maule earthquake (M8.8) triggered a shallow M7 earthquake on the Pichilemu fault, which had not been mapped and was unknown. In fact, M~7 earthquakes have recently occurred along unknown faults in California and New Zealand, emphasizing the need for better and more detailed mapping initiatives. A first step towards a synoptic assessment of seismic hazards posed by continental faults at the national level is mapping at a homogeneous scale to allow for a systematic comparison of faults and fault systems. Here, we present the first map of active and potentially-active faults in Chile at 1:25,000 scale, which includes published studies and newly-identified faults. All the published faults have been re-mapped using LiDAR and TanDEM-X topography, where available. Using different scaling relations, we estimate the seismic potential of all crustal faults in Chile. For specific faults where we have conducted paleoseismic and tectonic geomorphic field studies (e.g., Liqui&#241;e-Ofqui, El Yolki, Mesamavida, and Pichilemu faults) we provide new estimates of slip rate, recurrence interval, and deformation style. We propose a segmentation model of continental faults systems in Chile, which are associated with distinct morphotectonic units and have predominant kinematics and relatively uniform slip rates. Using stress transfer models, we explore the potential feedbacks between upper-plate deformation and the megathrust seismic cycle.

Download Full-text

Enhancement of Interplate Coupling after Recent Megathrust Earthquakes

10.5194/egusphere-egu2020-2550 ◽

2020 ◽

Author(s):

Mohammad Yuzariyadi ◽

Kosuke Heki

Keyword(s):

Subduction Zones ◽

Megathrust Earthquakes ◽

The North ◽

Rupture Area ◽

Interplate Coupling ◽

Maule Earthquake ◽

Megathrust Faults ◽

Adjacent Segments ◽

Gnss Data ◽

Ne Japan

Enhanced interplate coupling has been found for segments adjacent along-strike to megathrust faults after the 2003 Tokachi-Oki and the 2011 Tohoku-Oki earthquakes, NE Japan, and was interpreted as acceleration of the subducting Pacific Plate slab. A similar enhanced coupling was also reported for the segments to the north of the rupture area of the 2010 Maule earthquake, central Chile. We utilize available GNSS data to find such enhanced coupling in worldwide subduction zones including NE Japan, central and northern Chile, Sumatra, and Mexico to investigate their common features. Our study revealed that the accelerations of landward movement of 2.1-9.0 mm per year appeared in adjacent segments following the 2014 Iquique (Chile), the 2007 Bengkulu (Sumatra), and the 2012 Oaxaca (Mexico) earthquakes. We also confirmed that the enhanced coupling is associated with the increase of seismicity for all these six cases. We found that the degree of enhancement depends on the length of the slab and the magnitude of the earthquake, which is consistent with the simple 2-dimensional model proposed earlier.

Download Full-text

Joint estimate of the co-seismic 2011 Tohoku earthquake fault slip and post-seismic viscoelastic relaxation by GRACE data inversion

Geophysical Journal International ◽

10.1093/gji/ggz485 ◽

2019 ◽

Author(s):

G Cambiotti

Keyword(s):

Temporal Resolution ◽

Subduction Zones ◽

Gravity Data ◽

Tohoku Earthquake ◽

Fault Slip ◽

2011 Tohoku Earthquake ◽

The 2011 Tohoku Earthquake ◽

Physical Constraints ◽

Megathrust Earthquakes ◽

Grace Data

SUMMARY Satellite-derived gravity data offer a novel perspective for understanding the physics of megathrust earthquakes at subduction zones. Nonetheless, their temporal resolution and observational errors make it difficult to discern the different phases of the seismic cycle, as the elastostatic deformation (co-seismic) and the stress relaxation by viscous flow (post-seismic). To overcome these difficulties and to take advantage of the physical constraints on the temporal evolution and on the spatial pattern of the earthquake-induced gravity disturbances, we have jointly estimated the fault slip of the 2011 Tohoku earthquake and the rheological stratification by means of a Bayesian inversion of GRACE data time series and within the framework of spherically symmetric self-gravitating compressible viscoelastic Earth models. This approach, in addition to improve the exploitation of satellite-derived gravity data, allows us (i) to constrain the fault slip taking advantage of information from both the co- and post-seismic signatures and (ii) to investigate the trade-off between the fault slip and the shallow rheological stratification. In this respect, it can be used to improve the modelling of crustal displacements from GPS data, even if their higher accuracy and temporal resolution allow to discriminate well the co-seismic signature from the others.

Download Full-text

Spatial variations of incoming sediments at the northeastern Japan arc and their implications for megathrust earthquakes

Geology ◽

10.1130/g46757.1 ◽

2020 ◽

Vol 48 (6) ◽

pp. 614-619 ◽

Cited By ~ 4

Author(s):

Gou Fujie ◽

Shuichi Kodaira ◽

Yasuyuki Nakamura ◽

Jason P. Morgan ◽

Anke Dannowski ◽

...

Keyword(s):

Volcanic Activity ◽

Subduction Zones ◽

Tohoku Earthquake ◽

Northwestern Part ◽

Sediment Layer ◽

Oceanic Plate ◽

Coseismic Slip ◽

Acoustic Basement ◽

Seismic Reflection Data ◽

Megathrust Earthquakes

Abstract The nature of incoming sediments is a key controlling factor for the occurrence of megathrust earthquakes in subduction zones. In the 2011 Mw 9 Tohoku earthquake (offshore Japan), smectite-rich clay minerals transported by the subducting oceanic plate played a critical role in the development of giant interplate coseismic slip near the trench. Recently, we conducted intensive controlled-source seismic surveys at the northwestern part of the Pacific plate to investigate the nature of the incoming oceanic plate. Our seismic reflection data reveal that the thickness of the sediment layer between the seafloor and the acoustic basement is a few hundred meters in most areas, but there are a few areas where the sediments appear to be extremely thin. Our wide-angle seismic data suggest that the acoustic basement in these thin-sediment areas is not the top of the oceanic crust, but instead a magmatic intrusion within the sediments associated with recent volcanic activity. This means that the lower part of the sediments, including the smectite-rich pelagic red-brown clay layer, has been heavily disturbed and thermally metamorphosed in these places. The giant coseismic slip of the 2011 Tohoku earthquake stopped in the vicinity of a thin-sediment area that is just beginning to subduct. Based on these observations, we propose that post-spreading volcanic activity on the oceanic plate prior to subduction is a factor that can shape the size and distribution of interplate earthquakes after subduction through its disturbance and thermal metamorphism of the local sediment layer.

Download Full-text

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

Geophysical Research Letters ◽

10.1002/2013gl058886 ◽

2014 ◽

Vol 41 (4) ◽

pp. 1194-1201 ◽

Cited By ~ 19

Author(s):

Y. van Dinther ◽

P. M. Mai ◽

L. A. Dalguer ◽

T. V. Gerya

Keyword(s):

Subduction Zones ◽

Seismic Cycle ◽

Megathrust Earthquakes

Download Full-text

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

Earthquake Spectra ◽

10.1177/8755293019899957 ◽

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.

Download Full-text

Seismotectonic Deformations Related to the 2011 Tohoku Earthquake at Different Stages of the Seismic Cycle, Based on Satellite Geodetic Observations

Doklady Earth Sciences ◽

10.1134/s1028334x18080159 ◽

2018 ◽

Vol 481 (2) ◽

pp. 1060-1065

Author(s):

L. I. Lobkovsky ◽

I. S. Vladimirova ◽

Yu. V. Gabsatarov ◽

G. M. Steblov

Keyword(s):

Tohoku Earthquake ◽

2011 Tohoku Earthquake ◽

Seismic Cycle ◽

The 2011 Tohoku Earthquake

Download Full-text

A METHOD FOR THE DIRECT INTERPRETATION OF ELECTRICAL SOUNDINGS MADE OVER A FAULT OR DIKE

Geophysics ◽

10.1190/1.1440373 ◽

1973 ◽

Vol 38 (4) ◽

pp. 762-770 ◽

Cited By ~ 2

Author(s):

Terry Lee ◽

Ronald Green

Keyword(s):

Bessel Functions ◽

Direct Analysis ◽

Hankel Transform ◽

Approximation Technique ◽

Polarization Data ◽

Resistivity Data ◽

Vertical Fault ◽

Direct Interpretation ◽

Electrical Soundings ◽

Infinite Integral

The potential function for a point electrode in the vicinity of a vertical fault or dike may be expressed as an infinite integral involving Bessel functions. Beginning with such an expression, two methods are presented for the direct analysis of resistivity data measured both normal and parallel to dikes or faults. The first method is based on the asymptotic expansion of the Hankel transform of the field data and is suitable for surveys done parallel to the strike of the dike or fault. The second method is based on a successive approximation technique which starts from an initial approximate solution and iterates until a solution with prescribed accuracy is found. Both methods are suitable for programming on a digital computer and some illustrative numerical results are presented. These examples show the limitations of the methods. In addition, the application of resistivity data to the interpretation of induced‐polarization data is pointed out.

Download Full-text

Determination of the complex frequencies for the normal modes below 1mHz after the 2010 Maule and 2011 Tohoku earthquakes

Annals of Geophysics ◽

10.4401/ag-6400 ◽

2014 ◽

Vol 56 (5) ◽

Author(s):

Hao Ding ◽

Wen-Bin Shen

Keyword(s):

Time Series ◽

Normal Modes ◽

Power Spectra ◽

Tohoku Earthquake ◽

Superconducting Gravimeter ◽

Width Ratio ◽

Maule Earthquake ◽

Attenuation Models ◽

First Time

Based upon SG (superconducting gravimeter) records, the autoregressive method proposed by Chao and Gilbert [1980] is used to determine the frequencies of the singlets of seven spheroidal modes (0S2, 2S1, 0S3, 0S4, 1S2, 0S0, and 3S1) and the degenerate frequencies of three toroidal modes (0T2, 0T3, and 0T4) below 1 mHz after two recent huge earthquakes, the 2010 Mw8.8 Maule earthquake and the 2011 Mw9.1 Tohoku earthquake. The corresponding quality factor Qs are also determined for those modes, of which the Qs of the five singlets of 1S2 and the five singlets (m=0, m=±2, and m=±3) of 0S4 are estimated for the first time using the SG observations. The singlet m=0 of 3S1 is clearly observed from the power spectra of the SG time series without using other special spectral analysis methods or special time series from pole station records. In addition, the splitting width ratio R of 3S1 is 0.99, and consequently we conclude that 3S1 is normally split. The frequencies and Qs of the modes below 1mHz may contribute to refining the 3D density and attenuation models of the Earth.

Download Full-text

Subduction zone heterogeneity observed across the magnitude spectrum for megathrust earthquakes

10.5194/egusphere-egu21-8100 ◽

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

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.&#160; 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.&#160; 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.&#160; Estimates of small earthquake locations and stress drop are presented in each location, utilizing data from coastal and/or ocean bottom seismic stations.&#160; 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. &#160;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.&#160; Other variations in earthquake location and stress drop can be correlated with observed geodetic locking variations.&#160;

Download Full-text