scholarly journals Northern Chile intermediate-depth earthquakes controlled by plate hydration

2020 ◽  
Author(s):  
Leoncio Cabrera ◽  
Sergio Ruiz ◽  
Piero Poli ◽  
Eduardo Contreras-Reyes ◽  
Axel Osses ◽  
...  
Keyword(s):  
Template Matching ◽  
Thermal Structure ◽  
Seismic Source ◽  
Northern Chile ◽  
Large Magnitude ◽  
Aftershock Activity ◽  
Dramatic Decrease ◽  
Intermediate Depth ◽  
Subducting Plate

Summary We investigate the variations of the seismic source properties and aftershock activity using kinematic inversions and template-matching, for six large magnitude intermediate-depth earthquakes occurred in northern Chile. Results show similar rupture geometry and stress drop values between 7–30 MPa. Conversely, aftershocks productivity systematically decreases for the deeper events within the slab. Particularly there is a dramatic decrease in aftershock activity below the 400–450°C isotherm-depth, which separates high and low-hydrated zones. The events exhibit tensional focal mechanisms at unexpected depths within the slab, suggesting a deepening of the neutral plane, where the extensional regimen reaches the 700–800°C isotherm-depth. We interpret the reduction of aftershocks in the lower part of the extensional regime as the absence of a hydrated-slab at those depths. Our finding highlights the role of the thermal-structure and fluids in the subducting plate, in controlling the intermediated-depth seismic activity and shed new light in their causative mechanism.

Aftershock Activity at Intermediate-Depth Earthquakes in Northern Chile Controlled by Plate Hydration

2020 ◽  
Author(s):  
Leoncio Cabrera ◽  
Sergio Ruiz ◽  
Piero Poli ◽  
Eduardo Contreras-Reyes ◽  
Renzo Mancini ◽  
...  
Keyword(s):  
Template Matching ◽  
Broad Band ◽  
Strong Motion ◽  
Seismic Source ◽  
Northern Chile ◽  
Aftershock Activity ◽  
Study Region ◽  
Abrupt Decrease ◽  
Intermediate Depth ◽  
The Impact

<p>We investigate the differences of the seismic source and aftershock activity using kinematic inversions and template matching respectively, for the six largest intraslab intermediate-depth earthquakes occurred in northern Chile (Mw ~6.3) since 2010 at depths between 90 and 130 km and recorded by dense strong-motion and broad-band seismic networks. In addition, we developed a thermal model using the finite element method in the study region with the aim of analyze the impact of temperature on seismic behavior as the oceanic plate subducts. Our results show that geometries of rupture zones are similar, with semi-axis for an elliptical patch approach about 5 km, and stress drop values between 7 and 30 MPa. On the other hand, the number of aftershocks exhibits clear differences, and their amount decreases with increasing the depth within the slab bounded by the 450 ºC isotherm, which represents a limit between a high-hydrated and a dry or low-hydrated region. Furthermore, mainshocks occur at distances from the top of the slab from 7 to 40 km, and all of them exhibit normal focal mechanisms suggesting that the extensional regimen deepens within the slab to the 700-750 ºC isotherm-depth. We suggest that in northern Chile the abrupt decrease of aftershocks in the lower part of the extensional regimen is caused by the absence of a hydrated slab at those depths.</p>

scholarly journals Thermal structure and intermediate-depth seismicity in the Tohoku-Hokkaido subduction zones

Solid Earth ◽  
2012 ◽  
Vol 3 (2) ◽  
pp. 355-364 ◽  
Author(s):  
P. E. van Keken ◽  
S. Kita ◽  
J. Nakajima
Keyword(s):  
Subduction Zones ◽  
Thermal Structure ◽  
Finite Element Models ◽  
Local Conditions ◽  
Intermediate Depth ◽  
Upper Mantle Structure ◽  
Subduction System ◽  
Subducting Slab ◽  
Northern Japan

Abstract. The cause of intermediate-depth (>40 km) seismicity in subduction zones is not well understood. The viability of proposed mechanisms, which include dehydration embrittlement, shear instabilities and the presence of fluids in general, depends significantly on local conditions, including pressure, temperature and composition. The well-instrumented and well-studied subduction zone below Northern Japan (Tohoku and Hokkaido) provides an excellent testing ground to study the conditions under which intermediate-depth seismicity occurs. This study combines new finite element models that predict the dynamics and thermal structure of the Japan subduction system with a high-precision hypocenter data base. The upper plane of seismicity is principally contained in the crustal portion of the subducting slab and appears to thin and deepen within the crust at depths >80 km. The disappearance of seismicity overlaps in most of the region with the predicted phase change of blueschist to hydrous eclogite, which forms a major dehydration front in the crust. The correlation between the thermally predicted blueschist-out boundary and the disappearance of seismicity breaks down in the transition from the northern Japan to Kurile arc below western Hokkaido. Adjusted models that take into account the seismically imaged modified upper mantle structure in this region fail to adequately recover the correlation that is seen below Tohoku and eastern Hokkaido. We conclude that the thermal structure below Western Hokkaido is significantly affected by time-dependent, 3-D dynamics of the slab. This study generally supports the role of fluids in the generation of intermediate-depth seismicity.

scholarly journals Thermal structure and intermediate-depth seismicity in the Tohoku-Hokkaido subduction zones

2012 ◽  
Vol 4 (2) ◽  
pp. 1069-1093 ◽  
Author(s):  
P. E. van Keken ◽  
S. Kita ◽  
J. Nakajima
Keyword(s):  
Upper Mantle ◽  
Subduction Zones ◽  
Thermal Structure ◽  
Local Conditions ◽  
Intermediate Depth ◽  
Upper Mantle Structure ◽  
Subduction System ◽  
Subducting Slab ◽  
Northern Japan

Abstract. The cause of intermediate-depth (> 40 km) seismicity in subduction zones is not well understood. The viability of proposed mechanisms, that include dehydration embrittlement, shear instabilities, and the presence of fluids in general, depends significantly on local conditions, including pressure, temperature and composition. The well-instrumented and well-studied subduction zone below Northern Japan (Tohoku and Hokkaido) provides an excellent testing ground to study the conditions under which intermediate-depth seismicity occurs. This study combines new high resolution finite elements models that predict the dynamics and thermal structure of the Japan subduction system with a high precision hypocenter data base. The upper plane of seismicity is principally contained in the crustal portion of the subducting slab and appears to thin and deepen within the crust at depths > 80 km. The disappearance of seismicity overlaps in most of the region with the predicted phase change of blueschist to hydrous eclogite, which forms a major dehydration front in the crust. The correlation between thermally predicted blueschist-out boundary and the disappearance of seismicity breaks down in the transition from the northern Japan to Kurile arc below western Hokkaido. Adjusted models, that take into account the seismically imaged modified upper mantle structure in this region, fail to adequately recover the correlation that is seen below Tohoku and eastern Hokkaido. We conclude that the thermal structure below Western Hokkaido is significantly affected by time-dependent, 3-D dynamics of the slab. This study generally supports the role of fluids in the generation of intermediate-depth seismicity.

Estimating the accuracy of source “parameters”

1967 ◽  
Vol 57 (3) ◽  
pp. 373-379 ◽  
Author(s):  
Helen W. Freedman
Keyword(s):  
Standard Error ◽  
Source Parameters ◽  
Seismic Source ◽  
Origin Time ◽  
Intermediate Depth ◽  
Seismic Source Parameters ◽  
Space And Time

abstract This paper suggests a method for estimating the errors accompanying estimates of seismic source parameters. While the method is a general one, the data here are from 1962 and 1963 and special attention is given to a few regions, such as the Kuriles. The overall standard error of about one-half a degree in each coordinate and four seconds in origin time are broken down and analyzed in terms of magnitude, depth, and location in space and time. The most accurately located earthquakes appear to be those of intermediate depth and magnitude in highly seismic areas. There is some indication that these errors are decreasing with time.

scholarly journals On the role of dust storms in triggering atmospheric gravity waves observed in the middle atmosphere

2011 ◽  
Vol 29 (9) ◽  
pp. 1647-1654 ◽  
Author(s):  
S. K. Das ◽  
A. Taori ◽  
A. Jayaraman
Keyword(s):  
Gravity Waves ◽  
Dust Storm ◽  
Hot Spots ◽  
Middle Atmosphere ◽  
Thermal Structure ◽  
Dust Storms ◽  
Storm Events ◽  
Atmospheric Perturbations ◽  
Atmospheric Gravity

Abstract. Lower atmospheric perturbations often produce measurable effects in the middle and upper atmosphere. The present study demonstrates the response of the middle atmospheric thermal structure to the significant enhancement of the lower atmospheric heating effect caused by dust storms observed over the Thar Desert, India. Our study from multi-satellite observations of two dust storm events that occurred on 3 and 8 May 2007 suggests that dust storm events produce substantial changes in the lower atmospheric temperatures as hot spots which can become sources for gravity waves observed in the middle atmosphere.

scholarly journals Role of the stratospheric chemistry-climate interactions in the hot climate conditions of the Eocene

2018 ◽  
Author(s):  
Sophie Szopa ◽  
Rémi Thiéblemont ◽  
Slimane Bekki ◽  
Svetlana Botsyun ◽  
Pierre Sepulchre
Keyword(s):  
Thermal Structure ◽  
Stratospheric Ozone ◽  
Ozone Layer ◽  
Atmospheric Composition ◽  
Total Column Ozone ◽  
Climate Conditions ◽  
Ozone Distribution ◽  
Hot Climate ◽  
Ozone Column

Abstract. The stratospheric ozone layer plays a key role in atmospheric thermal structure and circulation. Although stratospheric ozone distribution is sensitive to changes in composition and climate, the modifications of stratospheric ozone are not usually considered in climate studies at geological time scales. Here, we evaluate with a chemical-climate model the potential role of stratospheric ozone chemistry in the case of the Eocene hot conditions. We show that the structure of the ozone layer is significantly different under these conditions (4×CO2 climate and high concentrations of tropospheric N2O and CH4). While at mid and high latitudes, the total column ozone is found to be enhanced, the tropical ozone column remains more or less unchanged. These ozone changes are related to the stratospheric cooling and an acceleration of stratospheric Brewer-Dobson circulation simulated under Eocene climate. The meridional distribution of the total ozone column appears also to be strongly modified, showing particularly pronounced mid-latitudes maxima and steeper negative poleward gradient from these maxima. These anomalies are consistent with changes in the seasonal evolution of the polar vortex during the winter, especially in the Northern Hemisphere. Compared to a pre-industrial atmospheric composition, the changes in local ozone concentration reach up to 40 % for zonal annual mean and affect temperature by a few Kelvins in the middle stratosphere. As inter-model differences in simulating the deep past temperatures are quite high, the consideration of atmospheric chemistry, which is computationally demanding in Earth system models, may seem superfluous. However, our results suggest that using stratospheric ozone calculated by the model (and hence more physically consistent with Eocene conditions) instead of the commonly specified preindustrial ozone distribution can change the simulated global surface air temperature by 14 %. This error is of the same order as the effect of non-CO2 boundary conditions (topography, bathymetry, solar constant & vegetation). Moreover, the results highlight the sensitivity of stratospheric ozone to hot climate conditions. Since the climate sensitivity to stratospheric ozone feedback largely differs between models, it must be better constrained not only for deep past conditions but also for future climates.

Reye Syndrome and Aspirin Use: The Role of Prodromal Illness Severity in the Assessment of Relative Risk

PEDIATRICS ◽  
1982 ◽  
Vol 69 (6) ◽  
pp. 822-825
Author(s):  
John T. Wilson ◽  
R. Don Brown
Keyword(s):  
Relative Risk ◽  
Infectious Diseases ◽  
Epidemiologic Study ◽  
Study Data ◽  
The State ◽  
Reye Syndrome ◽  
Confounding Variable ◽  
Large Magnitude ◽  
American Academy Of Pediatrics

In response to "Aspirin and Reye Syndrome" by the Committee on Infectious Diseases of the American Academy of Pediatrics (p 810), we offer comments which are restricted to our analysis of existing epidemiologic study data, portions of which were provided to us by the Ohio, Michigan, and Arizona investigators. This commentary should not be construed as our approval or disapproval of aspirin use in children. Rather, it summarizes our specific disagreements with the interpretation of the state epidemiologic data that were the basis of the report by the Committee on Infectious Diseases. We have found that an unassessed confounding variable of large magnitude is common to the state studies.

Water table variations in the hyperarid Atacama Desert: Role of the increasing groundwater extraction in the pampa del tamarugal (Northern Chile)

2019 ◽  
Vol 168 ◽  
pp. 9-16 ◽  
Author(s):  
Benoît Viguier ◽  
Hervé Jourde ◽  
Véronique Leonardi ◽  
Linda Daniele ◽  
Christelle Batiot-Guilhe ◽  
...  
Keyword(s):  
Water Table ◽  
Atacama Desert ◽  
Northern Chile ◽  
Groundwater Extraction ◽  
Pampa Del Tamarugal
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