Tonga Slab Morphology and Stress Variations Controlled by a Relic Slab: Implications for Deep Earthquakes in the Tonga‐Fiji Region

The multistage and discontinuous nature of the injection process used in the geological storage of CO2 causes reservoirs to experience repeated loading and unloading. The reservoir permeability changes caused by this phenomenon directly impact the CO2 injection process and the process of CO2 migration in the reservoirs. Through laboratory experiments, variations in the permeability of sandstone in the Liujiagou formation of the Ordos CO2 capture and storage (CCS) demonstration project were analyzed using cyclic variations in injection pressure and confining pressure and multistage loading and unloading. The variation in the micropore structure and its influence on the permeability were analyzed based on micropore structure tests. In addition, the effects of multiple stress changes on the permeability of the same type of rock with different clay minerals content were also analyzed. More attention should be devoted to the influence of pressure variations on permeability in evaluations of storage potential and studies of CO2 migration in reservoirs in CCS engineering.

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Depth dependence of rupture velocity in deep earthquakes

Geophysical Research Letters ◽

10.1029/2011gl046807 ◽

2011 ◽

Vol 38 (5) ◽

pp. n/a-n/a ◽

Cited By ~ 14

Author(s):

Mitsuru Suzuki ◽

Yuji Yagi

Keyword(s):

Rupture Velocity ◽

Depth Dependence ◽

Deep Earthquakes

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The excitation of tsunamis by deep earthquakes

Geophysical Journal International ◽

10.1093/gji/ggx013 ◽

2017 ◽

pp. ggx013

Author(s):

Emile A. Okal

Keyword(s):

Deep Earthquakes

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Deep earthquakes beneath central Taiwan: Mantle shearing in an arc-continent collision

Tectonics ◽

10.1029/92tc02812 ◽

1993 ◽

Vol 12 (3) ◽

pp. 745-755 ◽

Cited By ~ 13

Author(s):

C. H. Lin ◽

S. W. Roecker

Keyword(s):

Deep Earthquakes ◽

Central Taiwan

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Differences in the rupture process for very deep earthquakes at the Peru-Brazil and Peru-Bolivia borders

10.5194/egusphere-egu21-3256 ◽

2021 ◽

Author(s):

Elisa Buforn ◽

Carmen Pro ◽

Hernando Tavera ◽

Agustin Udias ◽

Maurizio Mattesini

Keyword(s):

Focal Depth ◽

Vertical Plane ◽

Rupture Process ◽

The South ◽

Nazca Plate ◽

Deep Earthquakes ◽

Pressure Axis ◽

Rate Functions ◽

The Moment ◽

Epicentral Location

<p>We analyze the differences in the rupture process for twelve very deep earthquakes (h>500 km) at the Peruvian-Brazilian subduction zone. These earthquakes are produced by the contact between the Nazca and the South America Plates. We have estimated the focal mechanism from teleseismic waveforms, using the slip inversion over the rupture plane, testing rupture velocities ranging from 2.5 km/s to 4.5 km/s, and analyzing the slip distribution for each &#160;rupture velocity. The selected 12 earthquakes have occurred in the period 1994- 2016, with magnitudes between 5.9 and 8.2 and focal depth 500- 700 km. They can be separated in two groups attending to their epicentral location. The first group is formed by 9 events located, in the Peruvian-Brazil border, with epicenters following a NNW-SSE alignment, parallel to the trench. Their focal mechanisms present solutions of normal faulting with planes oriented in NS direction, dipping about 45 degrees and with vertical pressure axis. The second group is formed by three earthquakes located to the south of the first group in northern Bolivia. Their mechanisms show dip-slip motion with a near vertical plane, oriented in NW-SE direction and the pressure axis dipping 45&#186; to the NE. The moment rate functions correspond to single ruptures with time durations from 6s to 12s, with the exception of the large 1994 Bolivian earthquake (Mw = 8.2) which presents a complex and longer STF. The different mechanisms for the two groups of earthquakes confirm the different dip of the subducting Nazca plate at the two areas, with the steeper part at the southern one. &#160;</p>

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A New Stress-Intensity Factor Solution for an External Surface Crack in Spheres

10.1115/pvp2021-61397 ◽

2021 ◽

Author(s):

James C. Sobotka ◽

Yi-Der Lee ◽

Joseph W. Cardinal ◽

R. Craig McClung

Keyword(s):

Stress Intensity Factor ◽

Finite Element ◽

Crack Front ◽

Surface Crack ◽

Degrees Of Freedom ◽

External Surface ◽

Crack Plane ◽

Finite Element Analyses ◽

Stress Variations ◽

Geometric Formulation

Abstract This paper describes a new stress-intensity factor (SIF) solution for an external surface crack in a sphere that expands capabilities previously available for this common pressure vessel geometry. The SIF solution employs the weight function (WF) methodology that enables rapid calculations of SIF values. The WF methodology determines SIF values from the nonlinear stress variations computed for the uncracked geometry, e.g., from service stresses and/or residual stresses. The current approach supports two degrees of freedom that denote the two crack tips located normal to the surface and the surface of the sphere. The geometric formulation of this solution enforces an elliptical crack front, maintains normality of the crack front with the free surface, and supports two degrees of freedom for fatigue crack growth from an internal crack tip and a surface crack tip. The new SIF solution accommodates spherical geometries with an exterior diameter greater than or equal to four times the thickness. This WF SIF solution has been combined with stress variations common for spherical pressure vessels: uniform internal pressure on the interior surface, uniform tension on the crack plane, and uniform bending on the crack plane. This paper provides a complete overview of this solution. We present for the first time the geometric formulation of the crack front that enables the new functionality and set the geometric limits of the solution, e.g., the maximum size and shape of the crack front. The paper discusses the bivariant WF formulation used to define the SIF solution and details the finite element analyses employed to calibrate terms in the WF formulation. A summary of preliminary verification efforts demonstrates the credibility of this solution against independent results from finite element analyses. We also compare results of this new solution against independent SIFs computed by finite element analyses, legacy SIF solutions, API 579, and FITNET. These comparisons indicate that the new WF solution compares favorably with results from finite element analyses. This paper summarizes ongoing efforts to improve and extend this solution, including formal verification and development of an internal surface crack model. Finally, we discuss the capabilities of this solution’s implementation in NASGRO® v10.0.

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