Geometric controls on megathrust earthquakes

2020 ◽  
Vol 222 (2) ◽  
pp. 1270-1282
Author(s):  
Steven M Plescia ◽  
Gavin P Hayes
Keyword(s):  
Subduction Zone ◽  
Subduction Zones ◽  
Earthquake Hazard ◽  
Earthquake Rupture ◽  
Primary Control ◽  
Slab Geometry ◽  
Megathrust Earthquakes ◽  
Maximum Earthquake Magnitude ◽  
Maximum Earthquake

SUMMARY The role of subduction zone geometry in the nucleation and propagation of great-sized earthquake ruptures is an important topic for earthquake hazard, since knowing how big an earthquake can be on a given fault is fundamentally important. Past studies have shown subducting bathymetric features (e.g. ridges, fracture zones, seamount chains) may arrest a propagating rupture. Other studies have correlated the occurrence of great-sized earthquakes with flat megathrusts and homogenous stresses over large distances. It remains unclear, however, how subduction zone geometry and the potential for great-sized earthquakes (M 8+) are quantifiably linked—or indeed whether they can be. Here, we examine the potential role of subduction zone geometry in limiting earthquake rupture by mapping the planarity of seismogenic zones in the Slab2 subduction zone geometry database. We build from the observation that historical great-sized earthquakes have preferentially occurred where the surrounding megathrust is broadly planar, and we use this relationship to search for geometrically similar features elsewhere in subduction zones worldwide. Assuming geometry exerts a primary control on earthquake propagation and termination, we estimate the potential size distribution of large (M 7+) earthquakes and the maximum earthquake magnitude along global subduction faults based on geometrical features alone. Our results suggest that most subduction zones are capable of hosting great-sized earthquakes over much of their area. Many bathymetric features previously identified as barriers are indistinguishable from the surrounding megathrust from the perspective of slab curvature, meaning that they either do not play an important role in arresting earthquake rupture or that their influence on slab geometry at depth is not resolvable at the spatial scale of our subduction zone geometry models.

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>

How Good is a Paleoseismic Record of Megathrust Earthquakes for Probabilistic Forecasting?

2021 ◽  
Author(s):  
Francisco Acuña ◽  
Gonzalo A. Montalva ◽  
Daniel Melnick
Keyword(s):  
Subduction Zones ◽  
Weibull Model ◽  
Time Dependent ◽  
Probabilistic Forecasting ◽  
Future Event ◽  
Earthquake Forecast ◽  
Megathrust Earthquakes ◽  
Chile Earthquake ◽  
Hazard Assessments

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.

scholarly journals Fluid pressurisation and earthquake propagation in the Hikurangi subduction zone

2021 ◽  
Author(s):  
Stefano Aretusini ◽  
Francesca Meneghini ◽  
Elena Spagnuolo ◽  
Christopher Harbord ◽  
Giulio Di Toro
Keyword(s):  
Shear Strength ◽  
Pore Pressure ◽  
Subduction Zone ◽  
Subduction Zones ◽  
Fluid Pressure ◽  
Low Permeability ◽  
Earthquake Rupture ◽  
Fault Rocks ◽  
Seismic Slip ◽  
Saturated Clay

<p>In subduction zones, seismic slip at shallow crustal depths can lead to the generation of tsunamis. Large slip displacements during tsunamogenic earthquakes are attributed to the low coseismic shear strength of the fluid-saturated and non-lithified clay-rich fault rocks. However, because of experimental challenges in confining these materials, the physical processes responsible of the coseismic reduction in fault shear strength are poorly understood. Using a novel experimental setup, we measured pore fluid pressure during simulated seismic slip in clay-rich materials sampled from the deep oceanic drilling of the Pāpaku thrust (Hikurangi subduction zone, New Zealand). Here we show that seismic slip is characterized by an initial decrease followed by an increase of pore pressure. The initial pore pressure decrease is indicative of dilatant behavior. The following pore pressure increase, enhanced by the low permeability of the fault, reduces the energy required to propagate earthquake rupture. We suggest that thermal and mechanical pressurisation of fluids facilitates seismic slip in the Hikurangi subduction zone, which was tsunamigenic about 70 years ago. Fluid-saturated clay-rich sediments, occurring at shallow depth in subduction zones, can promote earthquake rupture propagation and slip because of their low permeability and tendency to pressurise when sheared at seismic slip velocities.</p>

Anisotropy-revealed change in hydration along the Alaska subduction zone

Geology ◽  
2021 ◽  
Author(s):  
Colton Lynner
Keyword(s):  
Subduction Zone ◽  
Shear Wave ◽  
Subduction Zones ◽  
Seismic Anisotropy ◽  
Shear Wave Splitting ◽  
Pacific Plate ◽  
Seismic Gap ◽  
Megathrust Earthquakes ◽  
Wave Splitting ◽  
Subducting Slab

Megathrust earthquake behavior in subduction zones is controlled by a variety of factors including the hydration state of the subducting slab. Increased hydration reduces the occurrence of great, damaging earthquakes by diminishing the strength of the material along the interface between tectonic plates. Understanding variations in hydration in subductions zones is necessary for properly assessing the overall hazard posed by each region. Fortunately, seismic anisotropy is strongly dependent upon hydration of the subducting crust and lithosphere. I present shear-wave splitting measurements that illuminate changes in anisotropy, and therefore hydration, of the subducting Pacific plate beneath the Alaska subduction zone (northern Pacific Ocean). Variations in shear-wave splitting directly correlate to changes in the behavior of great, megathrust earthquakes. My measurements show that the Shumagin seismic gap is characterized by a hydrated subducting slab, explaining the long-term lack of great earthquakes. Observations in the immediately adjacent Semidi segment, which experiences great events regularly, indicate a far less hydrated slab. These results are driven by the preferential alignment of paleo-spreading fabrics of the Pacific plate. Where fabrics are more closely aligned with the orientation of the trench, outer-rise faulting and plate hydration is enhanced. These results highlight the importance of changes in preexisting slab structures and subsequent hydration in the production of great, damaging earthquakes.

scholarly journals Fluid pressurisation and earthquake propagation in the Hikurangi subduction zone

2021 ◽  
Vol 12 (1) ◽  
Author(s):  
S. Aretusini ◽  
F. Meneghini ◽  
E. Spagnuolo ◽  
C. W. Harbord ◽  
G. Di Toro
Keyword(s):  
Shear Strength ◽  
Subduction Zone ◽  
Subduction Zones ◽  
Seismic Velocity ◽  
Fluid Pressure ◽  
Velocity Shear ◽  
Low Permeability ◽  
Earthquake Rupture ◽  
Seismic Slip ◽  
Saturated Clay

AbstractIn subduction zones, seismic slip at shallow crustal depths can lead to the generation of tsunamis. Large slip displacements during tsunamogenic earthquakes are attributed to the low coseismic shear strength of the fluid-saturated and non-lithified clay-rich fault rocks. However, because of experimental challenges in confining these materials, the physical processes responsible for the coseismic reduction in fault shear strength are poorly understood. Using a novel experimental setup, we measured pore fluid pressure during simulated seismic slip in clay-rich materials sampled from the deep oceanic drilling of the Pāpaku thrust (Hikurangi subduction zone, New Zealand). Here, we show that at seismic velocity, shear-induced dilatancy is followed by pressurisation of fluids. The thermal and mechanical pressurisation of fluids, enhanced by the low permeability of the fault, reduces the energy required to propagate earthquake rupture. We suggest that fluid-saturated clay-rich sediments, occurring at shallow depth in subduction zones, can promote earthquake rupture propagation and slip because of their low permeability and tendency to pressurise when sheared at seismic slip velocities.

Main Results from the Program Promotion Panel for Subduction-Zone Earthquakes

2020 ◽  
Vol 15 (2) ◽  
pp. 87-95
Author(s):  
Kazushige Obara ◽  
Takuya Nishimura ◽  
◽  
Keyword(s):  
Subduction Zone ◽  
Subduction Zones ◽  
Deep Understanding ◽  
Disaster Mitigation ◽  
Observational Research ◽  
Earthquake Activity ◽  
Megathrust Earthquakes ◽  
Slow Earthquakes ◽  
Occurrence Mechanism ◽  
Subduction Zone Earthquakes

Understanding the occurrence mechanism of subduction zone earthquakes scientifically is intrinsically important for not only forecast of future subduction earthquakes but also disaster mitigation for strong ground motion and tsunami accompanied by large earthquakes. The Program Promotion Panel for Subduction-zone earthquakes mainly focused on interplate megathrust earthquakes in the subduction zones and the research activity included collection and classification of historical data on earthquake phenomena, clarifying the current earthquake phenomena and occurrence environment of earthquake sources, modelling earthquake phenomena, forecast of further earthquake activity based on monitoring crustal activity and precursory phenomena, and development of observation and analysis technique. Moreover, we studied the occurrence mechanism of intraslab earthquakes within the subducting oceanic plate. Five-year observational research program actually produced enormous results for deep understanding of subduction zone earthquakes phenomena, especially in terms of slow earthquakes, infrequent huge earthquakes, and intraslab earthquakes. This paper mainly introduces results from researches on these phenomena in subduction zones.

scholarly journals A Review of Tsunami Hazards in the Makran Subduction Zone

Geosciences ◽  
2020 ◽  
Vol 10 (9) ◽  
pp. 372
Author(s):  
Amin Rashidi ◽  
Denys Dutykh ◽  
Zaher Hossein Shomali ◽  
Nasser Keshavarz Farajkhah ◽  
Mohammadsadegh Nouri
Keyword(s):  
Subduction Zone ◽  
Subduction Zones ◽  
Tsunami Hazard ◽  
Makran Subduction Zone ◽  
Western Segment ◽  
History Of ◽  
Splay Faults ◽  
Almost All ◽  
New Evidence

The uncertain tsunamigenic potential of the Makran Subduction Zone (MSZ) has made it an interesting natural laboratory for tsunami-related studies. This study aims to review the recent activities on tsunami hazard in the Makran subduction zone with a focus on deterministic and probabilistic tsunami hazard assessments. While almost all studies focused on tsunami hazard from the Makran subduction thrust, other local sources such as splay faults and landslides can be also real threats in the future. Far-field tsunami sources such as Sumatra-Andaman and Java subduction zones, commonly lumped as the Sunda subduction zone, do not seem to pose a serious risk to the Makran coastlines. The tsunamigenic potential of the western segment of the MSZ should not be underestimated considering the new evidence from geological studies and lessons from past tsunamis in the world. An overview of the results of tsunami hazard studies shows that the coastal area between Kereti to Ormara along the shoreline of Iran-Pakistan and the coastal segment between Muscat and Sur along Oman’s shoreline are the most hazardous areas. Uncertainties in studying tsunami hazard for the Makran region are large. We recommend that future studies mainly focus on the role of thick sediments, a better understanding of the plates interface geometry, the source mechanism and history of extreme-wave deposits, the contribution of other local tsunamigenic sources and vulnerability assessment for all coastlines of the whole Makran region.

scholarly journals Cascadia megathrust earthquake rupture model constrained by geodetic fault locking

2021 ◽  
Vol 379 (2196) ◽  
pp. 20200135 ◽  
Author(s):  
Duo Li ◽  
Yajing Liu
Keyword(s):  
Subduction Zone ◽  
Subduction Zones ◽  
Seismogenic Zone ◽  
Cascadia Subduction Zone ◽  
Earthquake Rupture ◽  
Megathrust Earthquake ◽  
Fracture Dynamics ◽  
Coastal Marine ◽  
Rate And State Friction ◽  
Fault Locking

Paleo-earthquakes along the Cascadia subduction zone inferred from offshore sediments and Japan coastal tsunami deposits approximated to M9+ and ruptured the entire margin. However, due to the lack of modern megathrust earthquake records and general quiescence of subduction fault seismicity, the potential megathrust rupture scenario and influence of downdip limit of the seismogenic zone are still obscure. In this study, we present a numerical simulation of Cascadia subduction zone earthquake sequences in the laboratory-derived rate-and-state friction framework to investigate the potential influence of the geodetic fault locking on the megathrust sequences. We consider the rate-state friction stability parameter constrained by geodetic fault locking models derived from decadal GPS records, tidal gauge and levelling-derived uplift rate data along the Cascadia margin. We incorporate historical coseismic subsidence inferred from coastal marine sediments to validate our coseismic rupture scenarios. Earthquake rupture pattern is strongly controlled by the downdip width of the seismogenic, velocity-weakening zone and by the earthquake nucleation zone size. In our model, along-strike heterogeneous characteristic slip distance is required to generate margin-wide ruptures that result in reasonable agreement between the synthetic and observed coastal subsidence for the AD 1700 Cascadia Mw∼9.0 megathrust rupture. Our results suggest the geodetically inferred fault locking model can provide a useful constraint on earthquake rupture scenarios in subduction zones. This article is part of the theme issue ‘Fracture dynamics of solid materials: from particles to the globe’.

Petrologic and geochemical role of serpentinite in subduction zones and plate interface domains

2015 ◽  
Vol 37 ◽  
pp. 61-64
Author(s):  
Marco Scambelluri ◽  
Enrico Cannaò ◽  
Mattia Gilio ◽  
Marguerite Godard
Keyword(s):  
Subduction Zones ◽  
Plate Interface

THYROID STIMULATORS AND THYROID STIMULATION

1971 ◽  
Vol 66 (3) ◽  
pp. 558-576 ◽  
Author(s):  
Gerald Burke
Keyword(s):  
Regulatory System ◽  
Control Site ◽  
Thyroid Cell ◽  
Primary Control ◽  
Physico Chemical ◽  
Site Of Action ◽  
Long Acting

ABSTRACT A long-acting thyroid stimulator (LATS), distinct from pituitary thyrotrophin (TSH), is found in the serum of some patients with Graves' disease. Despite the marked physico-chemical and immunologic differences between the two stimulators, both in vivo and in vitro studies indicate that LATS and TSH act on the same thyroidal site(s) and that such stimulation does not require penetration of the thyroid cell. Although resorption of colloid and secretion of thyroid hormone are early responses to both TSH and LATS, available evidence reveals no basic metabolic pathway which must be activated by these hormones in order for iodination reactions to occur. Cyclic 3′, 5′-AMP appears to mediate TSH and LATS effects on iodination reactions but the role of this compound in activating thyroidal intermediary metabolism is less clear. Based on the evidence reviewed herein, it is suggested that the primary site of action of thyroid stimulators is at the cell membrane and that beyond the(se) primary control site(s), there exists a multifaceted regulatory system for thyroid hormonogenesis and cell growth.

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