scholarly journals Thermal squeezing of the seismogenic zone controlled rupture of the volcano-rooted Flores Thrust

2021 ◽  
Vol 7 (5) ◽  
pp. eabe2348
Author(s):  
Karen Lythgoe ◽  
Muzli Muzli ◽  
Kyle Bradley ◽  
Teng Wang ◽  
Andri Dian Nugraha ◽  
...  
Keyword(s):  
Thermal Structure ◽  
Critical Role ◽  
Volcanic Edifice ◽  
Seismic Array ◽  
Temperature Gradients ◽  
Seismogenic Zone ◽  
Arc Volcano

Temperature plays a critical role in defining the seismogenic zone, the area of the crust where earthquakes most commonly occur; however, thermal controls on fault ruptures are rarely observed directly. We used a rapidly deployed seismic array to monitor an unusual earthquake cascade in 2018 at Lombok, Indonesia, during which two magnitude 6.9 earthquakes with surprisingly different rupture characteristics nucleated beneath an active arc volcano. The thermal imprint of the volcano on the fault elevated the base of the seismogenic zone beneath the volcanic edifice by 8 km, while also reducing its width. This thermal “squeezing” directly controlled the location, directivity, dynamics, and magnitude of the earthquake cascade. Earthquake segmentation due to thermal structure can occur where strong temperature gradients exist on a fault.

scholarly journals Microseismicity constrains on the lithospheric structure at the ridge-transform intersection at the Romanche Transform Fault and Mid-Atlantic Ridge

2020 ◽  
Author(s):  
Zhiteng Yu ◽  
Satish C. Singh ◽  
Emma Gregory ◽  
Wayne Crawford ◽  
Marcia Maia ◽  
...  
Keyword(s):  
Thermal Structure ◽  
P Wave ◽  
Seismogenic Zone ◽  
Depth Range ◽  
Thermal Variation ◽  
Transform Fault ◽  
Pull Apart Basin ◽  
Mid Atlantic Ridge ◽  
Southern Border ◽  
Slow Spreading

<p>The Romanche Transform Fault (TF) in the equatorial Atlantic Ocean is the largest oceanic transform fault on Earth, offsetting the slow-spreading (2 cm/ yr) Mid-Atlantic Ridge (MAR) by 900-km and producing a maximum age contrast at the Ridge-Transform Intersection (RTI) of 45 Myr. This offset could cause a large thermal variation in the lithosphere around the RTI, but it is not known how this thermal variation would manifest itself. Here we present a ~21-day-long micro-earthquake study using a temporary deployment of 19 ocean-bottom seismometers (OBSs) during the 2019 SMARTIES cruise. 1363 earthquakes were detected on at least three OBSs and 622 could be located, of which 351 have high location accuracy (mean semi-major-axis of 3.9 km).</p><p>Linear (HYPOSAT) and non-linear (NonLinLoc) location algorithms reveal a similar earthquake distribution. Two event groups cluster at depths of 1) 0 km to ~18 km and 2) ~20 km to 30 km. Along the Romanche TF, micro-earthquakes are located beneath the southern border of the 30 km wide transform valley; no events are observed beneath the central or northern sections of the valley. These events' depths increase rapidly and linearly from a few km at the RTI to 30 km at 40 km along the transform fault, indicating a rapid increase in the thickness of the seismogenic zone (and lithosphere) along the transform fault. The presence of earthquakes on the southern border of the transform fault, which is younger and hence warmer, suggests that these events, and hence the seismogenic zone, follow an isotherm separating the brittle-ductile boundary. The absence of seismicity beneath the centre and northern boundary of the transform fault could be due to a much colder lithosphere and hence deeper ductile-brittle boundary.  </p><p>An aseismic gap exists beneath the pull-apart basin observed on bathymetry data. Beneath the RTI, earthquakes mainly occur in the 0-18 km depth range. Eight well-constrained focal mechanisms, derived from P-wave polarities, suggest that strike-slip faulting dominates along the transform fault. Normal faults are also observed, which may be attributed to an active detachment fault or pull-apart basin formation.</p><p>From the RTI to the tip of the southern MAR segment, micro-earthquakes show an undulating focal depth distribution from north to south. They can be summarized into three clustering groups: the RTI, the 16.6°W group, and the 16.2°W group. Micro-earthquakes beneath the MAR are mainly located in the axial valley. Events in the 16.6°W group mainly occur in the mantle at depths of 12-20 km, whereas those in the 16.2°W group are located at shallow depths of 2-12 km, which is similar to that observed along other slow-spreading Mid-Ocean Ridges. This evidence indicates that there are significant variations in the along-axis thermal structure of the lithosphere along the rift axis.</p><p>ZY acknowledges the China Postdoctoral Science Foundation (2019M652041, BX20180080); DB acknowledges funding PRIN2017KY5ZX8.</p>

scholarly journals Crustal Thermal Structure and Exhumation Rates in the Southern Alps Near the Central Alpine Fault, New Zealand

2021 ◽  
Author(s):  
K Michailos ◽  
Rupert Sutherland ◽  
John Townend ◽  
Martha Savage
Keyword(s):  
New Zealand ◽  
Thermal Structure ◽  
Hanging Wall ◽  
Southern Alps ◽  
Seismogenic Zone ◽  
Fixed Temperature ◽  
Alpine Fault ◽  
Brittle Ductile Transition ◽  
Orogenic Uplift ◽  
Exhumation Rates

© 2020. American Geophysical Union. All Rights Reserved. We investigate orogenic uplift rates and the thermal structure of the crust in the hanging wall of the Alpine Fault, New Zealand, using the hypocenters of 7,719 earthquakes that occurred in the central Southern Alps between late 2008 and early 2017, and previously published thermochronological data. We assume that the base of the seismogenic zone corresponds to a brittle-ductile transition at some fixed temperature, which we estimate by fitting the combined thermochronological data and distribution of seismicity using a multi-1-D approach. We find that exhumation rates vary from 1 to 8 mm/yr, with maximum values observed in the area of highest topography near Aoraki/Mount Cook, a finding consistent with previous geologic and geodetic analyses. We estimate the temperature of the brittle-ductile transition beneath the Southern Alps to be 410–430°C, which is higher than expected for Alpine Fault rocks whose bulk lithology is likely dominated by quartz. The high estimated temperatures at the base of the seismogenic zone likely reflect the unmodeled effects of high fluid pressures or strain rates.

Warm thermal structures in subduction zones lead to ample dehydration at the depths of deep slow slip and tremor and resultant transformations in viscous rheology 

2021 ◽  
Author(s):  
Cailey Condit ◽  
Victor Guevara ◽  
Melodie French ◽  
Adam Holt ◽  
Jonathan Delph
Keyword(s):  
Subduction Zones ◽  
Thermal Structure ◽  
Fluid Pressure ◽  
Plate Boundary ◽  
Pore Fluid ◽  
Seismogenic Zone ◽  
Plate Interface ◽  
Dehydration Reactions ◽  
Episodic Tremor And Slip ◽  
Increased Strength

<p>Feedbacks amongst petrologic and mechanical processes along the subduction plate boundary play a central role influencing slip behaviors and deformation styles. Metamorphic reactions, resultant fluid production, deformation mechanisms, and strength are strongly temperature dependent, making the thermal structure of these zones a key control on slip behaviors.</p><p> </p><p>Firstly, we investigate the role of metamorphic devolatilization reactions in the production of Episodic Tremor and Slip (ETS) in warm subduction zones. Geophysical and geologic observations of ETS hosting subduction zones suggest the plate interface is fluid-rich and critically stressed, which together, suggests that this area is a zone of near lithostatic pore fluid pressure.  Fluids and high pore fluid pressures have been invoked in many models for ETS. However, whether these fluids are sourced from local dehydration reactions in particular lithologies, or via up-dip transport from greater depths remains an open question. We present thermodynamic models of the petrologic evolution of four lithologies typical of the plate interface along predicted pressure–temperature (P-T) paths for the plate boundary along Cascadia, Nankai, and Mexico which all exhibit ETS at depths between 25-65 km. Our models suggest that 1-2 wt% H<sub>2</sub>O is released at the depths of ETS along these subduction segments due to punctuated dehydration reactions within MORB, primarily through chlorite and/or lawsonite breakdown. These reactions produce sufficient in-situ fluid across this narrow P-T range to cause high pore fluid pressures. Punctuated dehydration of oceanic crust provides the dominant source of fluids at the base of the seismogenic zone in these warm subduction margins, and up-dip migration of fluids from deeper in the subduction zone is not required to produce ETS-facilitating high pore fluid pressures. These dehydration reactions not only produce metamorphic fluids at these depths, but also result in an increased strength of viscous deformation through the breakdown of weak hydrous phases (e.g., chlorite, glaucophane) and the growth of stronger minerals (e.g., garnet, omphacite, Ca-amphibole). Lastly, we present preliminary data on viscosity along warm subduction paths showing the locations of these dehydration pulses correlate with viscosity increases in mafic lithologies along the shallow forarc.</p>

Thermal structure of the Amery Ice Shelf from borehole observations and simulations

2021 ◽  
Author(s):  
Yu Wang ◽  
Chen Zhao ◽  
Rupert Gladstone ◽  
Ben Galton-Fenzi
Keyword(s):  
Boundary Conditions ◽  
Mass Balance ◽  
Thermal Structure ◽  
Three Dimensional ◽  
Temperature Gradients ◽  
Temperature Fields ◽  
Large Temperature ◽  
Temperature Profiles ◽  
Ice Shelf ◽  
Amery Ice Shelf

<p>The Amery Ice Shelf (AIS), East Antarctica, has a layered structure, due to the presence of both meteoric and marine ice. In this study, the thermal structures of the AIS are evaluated from vertical temperature profiles, and its formation mechanism are demonstrated by numerical simulations. The temperature profiles, derived from borehole thermistor data at four different locations, indicate distinct temperature regimes in the areas with and without basal marine ice. The former shows a near-isothermal layer over 100 m at the bottom and stable internal temperature gradients, while the latter reveals a cold core ice resulting from upstream cold ice advection and large temperature gradients within 90 m at the bottom. The three-dimensional steady-state temperature fields are simulated by Elmer/Ice, a full-stokes ice sheet model, using three different basal mass balance datasets. We found the simulated temperature fields are highly sensitive to the choice of dynamic boundary conditions on both upper and lower surfaces. To better illustrate the formation of the vertical thermal regimes, we construct a one-dimensional temperature column model to simulate the process of ice columns moving on the flowlines with varying boundary conditions. The comparison of simulated and observed temperature profiles suggests that the basal mass balance and meteoric ice advection are both crucial factors determining the thermal structure of the ice shelf. The different basal mass balance datasets are indirectly evaluated as well. The improved understanding of the thermal structure of the AIS will assist with further studies on its thermodynamics and rheology.</p>

scholarly journals The Effect of the Ocean Eddy on Tropical Cyclone Intensity

2007 ◽  
Vol 64 (10) ◽  
pp. 3562-3578 ◽  
Author(s):  
Chun-Chieh Wu ◽  
Chia-Ying Lee ◽  
I-I. Lin
Keyword(s):  
Tropical Cyclone ◽  
Tropical Cyclones ◽  
Mixed Layer ◽  
Thermal Structure ◽  
Critical Role ◽  
Strong Mixing ◽  
Rapid Intensification ◽  
Tropical Cyclone Intensity ◽  
Cyclone Intensity ◽  
The Impact

Abstract The rapid intensification of Hurricane Katrina followed by the devastation of the U.S. Gulf States highlights the critical role played by an upper-oceanic thermal structure (such as the ocean eddy or Loop Current) in affecting the development of tropical cyclones. In this paper, the impact of the ocean eddy on tropical cyclone intensity is investigated using a simple hurricane–ocean coupled model. Numerical experiments with different oceanic thermal structures are designed to elucidate the responses of tropical cyclones to the ocean eddy and the effects of tropical cyclones on the ocean. This simple model shows that rapid intensification occurs as a storm encounters the ocean eddy because of enhanced heat flux. While strong winds usually cause strong mixing in the mixed layer and thus cool down the sea surface, negative feedback to the storm intensity of this kind is limited by the presence of a warm ocean eddy, which provides an insulating effect against the storm-induced mixing and cooling. Two eddy factors, FEDDY-S and FEDDY-T, are defined to evaluate the effect of the eddy on tropical cyclone intensity. The efficiency of the eddy feedback effect depends on both the oceanic structure and other environmental parameters, including properties of the tropical cyclone. Analysis of the functionality of FEDDY-T shows that the mixed layer depth associated with either the large-scale ocean or the eddy is the most important factor in determining the magnitude of eddy feedback effects. Next to them are the storm’s translation speed and the ambient relative humidity.

scholarly journals Numerical Simulation of the Effects of Wedge Subduction on the Lithospheric Thermal Structure and the Seismogenic Zone South of Chile Triple Junction

2021 ◽  
Vol 9 ◽  
Author(s):  
Changsheng Guo ◽  
Pengchao Sun ◽  
Dongping Wei
Keyword(s):  
Convergence Rate ◽  
Triple Junction ◽  
Thermal Structure ◽  
Focal Depth ◽  
Seismogenic Zone ◽  
Nazca Plate ◽  
Thick Part ◽  
Lithospheric Thermal Structure ◽  
Chile Triple Junction ◽  
The Antarctic

In contrast to common subduction, the young and thin part of the Antarctic Plate subducts first to the south of the Chile Triple Junction (CTJ), followed by the old and thick part, corresponding to wedge subduction. A finite element model was used to simulate the wedge subduction of the Antarctic Plate and to compare it with the slab subduction of the Nazca Plate. The results show that the CTJ is not only a wedge subduction boundary but also an important factor controlling the lithospheric thermal structure of the overriding plate. The computed heat flow curves are consistent with the data observed near the trench of the two selected profiles. The different slab dips to the north and south of the CTJ are considered to be caused by wedge subduction. When the slabs are young and at the same age, the deep dip of the Antarctic slab is 22° smaller than the Nazca slab. Southward from the CTJ, the slab age of the wedge subduction increases, which leads to a larger slab dip, a colder slab, and a wider seismogenic zone. The effect of the slab age of wedge subduction on the focal depth is smaller than that of the convergence rate. A 4.8-cm/year difference in convergence rate of the wedge subduction results in an 11-km difference in the width of the seismogenic zone and a 10-km difference in the depth of the downdip limit. Among these controlling factors, the convergence rate plays a major role in the different focal depths south and north of the CTJ.

scholarly journals Self-Organization of Atmospheric Macroturbulence into Critical States of Weak Nonlinear Eddy–Eddy Interactions

2006 ◽  
Vol 63 (6) ◽  
pp. 1569-1586 ◽  
Author(s):  
Tapio Schneider ◽  
Christopher C. Walker
Keyword(s):  
Surface Temperature ◽  
Thermal Stratification ◽  
Nonlinear Models ◽  
Thermal Structure ◽  
Baroclinic Instability ◽  
Temperature Gradients ◽  
Tropopause Height ◽  
Weakly Nonlinear ◽  
Critical States ◽  
Inverse Energy Cascade

Abstract It is generally held that atmospheric macroturbulence can be strongly nonlinear. Yet weakly nonlinear models successfully account for scales and structures of baroclinic eddies in Earth's atmosphere. Here a theory and simulations with an idealized GCM are presented that suggest weakly nonlinear models are so successful because atmospheric macroturbulence organizes itself into critical states of weak nonlinear eddy–eddy interactions. By modifying the thermal structure of the extratropical atmosphere such that its supercriticality remains limited, macroturbulence inhibits nonlinear eddy–eddy interactions and the concomitant inverse energy cascade from the length scales of baroclinic instability to larger scales. For small meridional surface temperature gradients, the extratropical thermal stratification and tropopause height are set by radiation and convection, and the supercriticality is less than one; for sufficiently large meridional surface temperature gradients, the extratropical thermal stratification and tropopause height are modified by baroclinic eddies such that the supercriticality does not significantly exceed one. In either case, the scale of the energy-containing eddies is similar to the scale of the linearly most unstable baroclinic waves, and eddy kinetic and available potential energies are equipartitioned. The theory and simulations point to fundamental constraints on the thermal structures and global circulations of the atmospheres of Earth and other planets, for example, by providing limits on the tropopause height and estimates for eddy scales, eddy energies, and jet separation scales.

scholarly journals Three-dimensional thermal structure of subduction zones: effects of obliquity and curvature

2012 ◽  
Vol 4 (2) ◽  
pp. 919-941 ◽  
Author(s):  
A. K. Bengtson ◽  
P. E. van Keken
Keyword(s):  
Cross Section ◽  
Cross Sections ◽  
Subduction Zones ◽  
Mantle Wedge ◽  
Thermal Structure ◽  
Critical Role ◽  
Three Dimensional ◽  
Arc Volcanism ◽  
Oblique Subduction ◽  
Dehydration Reactions

Abstract. Quantifying the precise thermal structure of subduction zones is essential for understanding the nature of metamorphic dehydration reactions, arc volcanism, and intermediate depth seismicity. High resolution two-dimensional (2-D) models have shown that the rheology of the mantle wedge plays a critical role and establishes strong temperature gradients in the slab. The influence of three-dimensional (3-D) subduction zone geometry on thermal structure is however not yet well characterized. A common assumption for 2-D models is that the cross-section is taken normal to the strike of the trench with a corresponding velocity reduction in the case of oblique subduction, rather than taken parallel to velocity. A comparison between a full 3-D Cartesian model with oblique subduction and selected 2-D cross-sections demonstrates that the trench-normal cross-section provides a better reproduction of the slab thermal structure than the velocity-parallel cross-section. An exception is found in the case of strongly curved subduction, such as in the Marianas, where strong 3-D flow in the mantle wedge is generated. In this case it is shown that the full 3-D model should be evaluated for an accurate prediction of the slab thermal structure.

scholarly journals Revisiting evidence for widespread seismicity in the upper mantle under Los Angeles

2021 ◽  
Vol 7 (4) ◽  
pp. eabf2862
Author(s):  
Lei Yang ◽  
Xin Liu ◽  
Gregory C. Beroza
Keyword(s):  
Stress Concentration ◽  
Los Angeles ◽  
Upper Mantle ◽  
Active Faults ◽  
Fault Zones ◽  
Seismic Array ◽  
Seismogenic Zone ◽  
Long Beach ◽  
Back Projection ◽  
Deep Seismicity

We revisit the finding of widespread deep seismicity in the upper mantle imaged with a dense, temporary nodal seismic array in Long Beach, California using back-projection to detect candidate events and trace randomization to develop a reliable imaging threshold for candidate detections. We find that nearly all detections of small events at depths greater than 20 kilometers in the upper mantle fall below the reliability threshold. We find a modest number of small, shallower events in the crust that appear to align with the active Newport-Inglewood Fault. These events occur primarily at 15- to 20-kilometer depth near the base of the seismogenic zone. Localized seismicity under fault zones suggests that the deep extensions of active faults are localized and deforming, with stress concentration leading to a concentration of small events, near the seismic-aseismic transition.

scholarly journals Crustal Thermal Structure and Exhumation Rates in the Southern Alps Near the Central Alpine Fault, New Zealand

2021 ◽  
Author(s):  
K Michailos ◽  
Rupert Sutherland ◽  
John Townend ◽  
Martha Savage
Keyword(s):  
New Zealand ◽  
Thermal Structure ◽  
Hanging Wall ◽  
Southern Alps ◽  
Seismogenic Zone ◽  
Fixed Temperature ◽  
Alpine Fault ◽  
Brittle Ductile Transition ◽  
Orogenic Uplift ◽  
Exhumation Rates

© 2020. American Geophysical Union. All Rights Reserved. We investigate orogenic uplift rates and the thermal structure of the crust in the hanging wall of the Alpine Fault, New Zealand, using the hypocenters of 7,719 earthquakes that occurred in the central Southern Alps between late 2008 and early 2017, and previously published thermochronological data. We assume that the base of the seismogenic zone corresponds to a brittle-ductile transition at some fixed temperature, which we estimate by fitting the combined thermochronological data and distribution of seismicity using a multi-1-D approach. We find that exhumation rates vary from 1 to 8 mm/yr, with maximum values observed in the area of highest topography near Aoraki/Mount Cook, a finding consistent with previous geologic and geodetic analyses. We estimate the temperature of the brittle-ductile transition beneath the Southern Alps to be 410–430°C, which is higher than expected for Alpine Fault rocks whose bulk lithology is likely dominated by quartz. The high estimated temperatures at the base of the seismogenic zone likely reflect the unmodeled effects of high fluid pressures or strain rates.

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