Stress Drop Mapping in the Northern Chilean Subduction Zone

2020 ◽  
Author(s):  
Jonas Folesky ◽  
Joern Kummerow ◽  
Serge A. Shapiro
Keyword(s):  
Subduction Zone ◽  
Stress Drop ◽  
Observation Interval ◽  
Spectral Ratio ◽  
Temporal Variations ◽  
Data Set ◽  
Systematic Analysis ◽  
Megathrust Earthquakes ◽  
Time Period ◽  
Stress Drops

<p>The Northern Chilean subduction zone has been monitored by the IPOC network for more than ten years. During this time period two very large earthquakes occurred, the 2007 M<sub>W</sub>7.7  Tocopilla earthquake and the 2014 M<sub>W</sub>8.1 Iquique earthquake. Over the entire subduction zone a vast amount of seismic activity has been recorded and a huge catalog was compiled including over 100000 events (Sippl et al. 2018). With this exceptional data base we attempt a systematic analysis of the stress drops of as many events from the catalog as possible. We apply different estimation techniques, namely the spectral ratio type, the spectral stacking approach, and the lower bound method. A goal of our research is a comparison and possibly a combination of the techniques to obtain reliable and well constrained results.</p><p>The data set covers events at the interface, within the subducting plate, crustal events, and intermediate depth events. It therefore bears a great potential to better understand the stress drop distribution within a subduction zone. Also, the long observation interval allows to analyze temporal variations according to pre-, inter-, and post-seismic phases of megathrust earthquakes.   </p><p>We present preliminary results where a subset of 730 events with a magnitude range of M<sub>L</sub>2.7 - M<sub>L</sub>4.8  was used for analysis with the spectral ratio technique. For these events we show maps of spatial stress drop variation, and we analyze the time dependent stress drop variance. </p>

Stress Drops from Trench to Depth in the Northern Chilean Subduction Zone

2021 ◽  
Author(s):  
Jonas Folesky ◽  
Rens Hofman ◽  
Jörn Kummerow
Keyword(s):  
Subduction Zone ◽  
Stress Drop ◽  
Template Matching ◽  
High Stress ◽  
Spectral Ratio ◽  
Observation Time ◽  
Data Set ◽  
First Results ◽  
Depth Dependency ◽  
Stress Drops

<div> <div> <div> <p>At the northern Chilean subduction zone the IPOC network monitors seismicity since 2007. During the observation time period two very large earthquakes occurred, the 2007 MW 7.7 Tocopilla earthquake and the 2014 MW 8.1 Iquique earthquake and until today the subduction zone shows a vast amount of seismic activity. A large catalog was compiled and published including over 100000 events by Sippl et al. 2018. Therein, seismicity ranges from close to the trench till deep into the mantle to about 300km depth. Consequently, events occur under a broad variability of physical conditions.</p> <p>We extend the aforementioned catalog by applying a template matching technique to identify additional events, that are colocated with catalog events. Based on these events we apply an empirical Green’s function method called spectral ratio approach to estimate stress drops. The results cover different nucleation provinces i.e. the data set includes stress drops obtained at the interface, within the subducting plate, from crustal events, intermediate depth events, and from deep to very deep seismicity. The study therefore bears a great potential to better understand the stress drop distribution within an entire subduction zone.</p> </div> </div> </div><p>First results show no depth dependency in the shallowest 100 km but spatial variability with high stress drops focused to particular regions on the interface. We also find increased stress drop values in the crust when compared to events close or at the interface.</p>

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>

Source parameters for aftershocks of the Oroville, California, earthquake

1984 ◽  
Vol 74 (4) ◽  
pp. 1101-1123
Author(s):  
Jon Fletcher ◽  
John Boatwright ◽  
Linda Haar ◽  
Thomas Hanks ◽  
Art McGarr
Keyword(s):  
Stress Drop ◽  
Dynamic Stress ◽  
Depth Interval ◽  
Causal Mechanism ◽  
Overburden Pressure ◽  
Data Set ◽  
State Of Stress ◽  
Aftershock Sequences ◽  
Least Squares Fit ◽  
Stress Drops

Abstract A suite of 111 strong-motion accelerograms for 14 aftershocks of the Oroville, California, earthquake (ML = 5.7, 1 August 1975) that range in local magnitude (ML) from 2.8 to 5.2 has been analyzed to obtain estimates of seismic moment (Mo), source radius (ro), and stress drop (Δσ) in addition to the focal parameters of location, depth, and fault-plane solution. This data set, which is unusually complete for near-source (Δ ≲ 20 km) on-scale readings, allows for greater precision in the calculation of various measures of stress difference as represented by the Brune stress drop, the apparent stress, the arms stress drop, and the dynamic stress drop. In addition, the seismicity following each aftershock and state-of-stress seem to correlate with particular estimates of stress drop. Seismic moments were calculated from the asymptotic long-period spectral levels which were corrected for the radiation pattern of a double-couple point source. They range from 1.4 × 1021 dyne-cm for a ML = 2.8 shock to 3.3 × 1023 dyne-cm for a ML = 5.1 event. A least-squares fit between ML and the logarithm Mo yields log M 0 = ( 1.36 ± 0.22 ) M L + ( 16.8 ± 1.1 ) for M L ≧ 4.3 and log ⁡ M 0 = ( 1.1 ± 0.14 ) M L + ( 18 ± 0.51 ) for M L ≦ 4.1. These relationships are qualitatively in agreement with the response of the Wood-Anderson instrument to a Brune pulse. Stress drops from the Brune formulation range about 14 to 170 bars. Stress drop is correlated with depth in that the deepest events have the largest stress drops and no large stress drops occur at the shallow depths. Apparent stresses are smaller than the Brune stress drops and show a weaker depth dependence over the depth interval for which they are available. The stress drop calculated from the rms of acceleration (arms) was approximately constant at about 90 bars for 5 of the 7 larger events analyzed; the two high values of 160 and 190 bars were obtained only for the two events which had marked aftershock sequences of their own. These results may be interpreted in terms of the state-of-stress, simple fracture criteria, and mechanisms for the generation of aftershocks. The increase with depth of the envelope of the Brune stress drops may be caused by an increase in shear stress from overburden pressure. Smaller stress drop events can occur at any depth interval. The causal mechanism of aftershocks is not known, but probably includes a change in the frictional properties of the fault, suggesting that the arms stress drop is a measure of the frictional or dynamic stress release.

scholarly journals Spatio-temporal analysis of seismic anisotropy associated with the Cook Strait and Kaikōura earthquake sequences in New Zealand

2021 ◽  
Author(s):  
KM Graham ◽  
Martha Savage ◽  
Richard Arnold ◽  
HJ Zal ◽  
T Okada ◽  
...  
Keyword(s):  
New Zealand ◽  
Seismic Anisotropy ◽  
Temporal Analysis ◽  
Temporal Variations ◽  
Orthogonal Direction ◽  
Data Set ◽  
Systematic Analysis ◽  
Crustal Earthquakes ◽  
Cook Strait ◽  
Earthquake Sequences

© 2020 The Author(s) 2020. Published by Oxford University Press on behalf of The Royal Astronomical Society. Large earthquakes can diminish and redistribute stress, which can change the stress field in the Earth's crust. Seismic anisotropy, measured through shear wave splitting (SWS), is often considered to be an indicator of stress in the crust because the closure of cracks due to differential stress leads to waves polarized parallel to the cracks travelling faster than in the orthogonal direction. We examine spatial and temporal variations in SWS measurements and the Vp/Vs ratio associated with the 2013 Cook Strait (Seddon, Grassmere) and 2016 Kaikōura earthquakes in New Zealand. These earthquake sequences provide a unique data set, where clusters of closely spaced earthquakes occurred. We use an automatic, objective splitting analysis algorithm and automatic local S-phase pickers to expedite the processing and to minimize observer bias. We present SWS and Vp/Vs measurements for over 40 000 crustal earthquakes across 36 stations spanning close to $5\frac{1}{2}$ yr between 2013 and 2018. We obtain a total of 102 260 (out of 398 169) high-quality measurements. We observe significant spatial variations in the fast polarization orientation, φ. The orientation of gravitational stresses are consistent with most of the observed anisotropy. However, multiple mechanisms (such as structural, tectonic stresses and gravitational stresses) may control some of the observed crustal anisotropy in the study area. Systematic analysis of SWS parameters and Vp/Vs ratios revealed that apparent temporal variations are caused by variation in earthquake path through spatially varying media.

scholarly journals Spatio-temporal analysis of seismic anisotropy associated with the Cook Strait and Kaikōura earthquake sequences in New Zealand

2020 ◽  
Vol 223 (3) ◽  
pp. 1987-2008
Author(s):  
Kenny M Graham ◽  
Martha K Savage ◽  
Richard Arnold ◽  
Hubert J Zal ◽  
Tomomi Okada ◽  
...  
Keyword(s):  
New Zealand ◽  
Seismic Anisotropy ◽  
Temporal Analysis ◽  
Temporal Variations ◽  
Orthogonal Direction ◽  
Data Set ◽  
Systematic Analysis ◽  
Crustal Earthquakes ◽  
Cook Strait ◽  
Earthquake Sequences

SUMMARY Large earthquakes can diminish and redistribute stress, which can change the stress field in the Earth’s crust. Seismic anisotropy, measured through shear wave splitting (SWS), is often considered to be an indicator of stress in the crust because the closure of cracks due to differential stress leads to waves polarized parallel to the cracks travelling faster than in the orthogonal direction. We examine spatial and temporal variations in SWS measurements and the Vp/Vs ratio associated with the 2013 Cook Strait (Seddon, Grassmere) and 2016 Kaikōura earthquakes in New Zealand. These earthquake sequences provide a unique data set, where clusters of closely spaced earthquakes occurred. We use an automatic, objective splitting analysis algorithm and automatic local S-phase pickers to expedite the processing and to minimize observer bias. We present SWS and Vp/Vs measurements for over 40 000 crustal earthquakes across 36 stations spanning close to $5\frac{1}{2}$ yr between 2013 and 2018. We obtain a total of 102 260 (out of 398 169) high-quality measurements. We observe significant spatial variations in the fast polarization orientation, ϕ. The orientation of gravitational stresses are consistent with most of the observed anisotropy. However, multiple mechanisms (such as structural, tectonic stresses and gravitational stresses) may control some of the observed crustal anisotropy in the study area. Systematic analysis of SWS parameters and Vp/Vs ratios revealed that apparent temporal variations are caused by variation in earthquake path through spatially varying media.

scholarly journals Spatio-temporal analysis of seismic anisotropy associated with the Cook Strait and Kaikōura earthquake sequences in New Zealand

2021 ◽  
Author(s):  
KM Graham ◽  
Martha Savage ◽  
Richard Arnold ◽  
HJ Zal ◽  
T Okada ◽  
...  
Keyword(s):  
New Zealand ◽  
Seismic Anisotropy ◽  
Temporal Analysis ◽  
Temporal Variations ◽  
Orthogonal Direction ◽  
Data Set ◽  
Systematic Analysis ◽  
Crustal Earthquakes ◽  
Cook Strait ◽  
Earthquake Sequences

© 2020 The Author(s) 2020. Published by Oxford University Press on behalf of The Royal Astronomical Society. Large earthquakes can diminish and redistribute stress, which can change the stress field in the Earth's crust. Seismic anisotropy, measured through shear wave splitting (SWS), is often considered to be an indicator of stress in the crust because the closure of cracks due to differential stress leads to waves polarized parallel to the cracks travelling faster than in the orthogonal direction. We examine spatial and temporal variations in SWS measurements and the Vp/Vs ratio associated with the 2013 Cook Strait (Seddon, Grassmere) and 2016 Kaikōura earthquakes in New Zealand. These earthquake sequences provide a unique data set, where clusters of closely spaced earthquakes occurred. We use an automatic, objective splitting analysis algorithm and automatic local S-phase pickers to expedite the processing and to minimize observer bias. We present SWS and Vp/Vs measurements for over 40 000 crustal earthquakes across 36 stations spanning close to $5\frac{1}{2}$ yr between 2013 and 2018. We obtain a total of 102 260 (out of 398 169) high-quality measurements. We observe significant spatial variations in the fast polarization orientation, φ. The orientation of gravitational stresses are consistent with most of the observed anisotropy. However, multiple mechanisms (such as structural, tectonic stresses and gravitational stresses) may control some of the observed crustal anisotropy in the study area. Systematic analysis of SWS parameters and Vp/Vs ratios revealed that apparent temporal variations are caused by variation in earthquake path through spatially varying media.

CHARACTERIZATION OF EXPOSURE TO ELECTROMAGNETIC EMISSIONS FROM PUBLIC MOBILE SYSTEMS USING THE TIME-AVERAGED AND INTEGRAL-BASED MEASURE

2020 ◽  
Vol 190 (2) ◽  
pp. 226-236
Author(s):  
Darko Šuka ◽  
Predrag Pejović ◽  
Mirjana Simić-Pejović
Keyword(s):  
Field Measurements ◽  
Temporal Variations ◽  
Mobile Systems ◽  
Data Set ◽  
Time Period ◽  
Monitoring Process ◽  
Short Term Exposure ◽  
Measurement Results ◽  
Electromagnetic Emissions ◽  
The Mean

Abstract Since radio frequency (RF) signals from public mobile systems are stochastic and exhibit large temporal variations, the results of measurements, typically E field measurements, are time dependent and highly variable. Therefore, any 6-min measurements and 6-min averaged results to obtain the mean level strength at a given place may not be so reliable when it comes to determine long-term exposure levels. Specifically, the results of such short-term exposure assessments can be both under- or overestimated depending on whether the extreme value is caught during the measurement time. Because the RF range is active 24 h a day, the authors suggest that the monitoring process should cover the same time period. To evaluate the variability of measurement results, the analysis in this paper was conducted through descriptive statistics of the 24-h instantaneous, time-averaged and integral-based values. By applying the 24-h time-averaged and integral-based measure on a 24-h data set of measurements, the variability of daily exposure could be reduced to ±20% of the mean week value obtained either with the time-averaged or integral-based measure.

scholarly journals A maximum rupture model for the central and southern Cascadia subduction zone—reassessing ages for coastal evidence of megathrust earthquakes and tsunamis

2021 ◽  
Vol 261 ◽  
pp. 106922
Author(s):  
Alan R. Nelson ◽  
Christopher B. DuRoss ◽  
Robert C. Witter ◽  
Harvey M. Kelsey ◽  
Simon E. Engelhart ◽  
...  
Keyword(s):  
Subduction Zone ◽  
Cascadia Subduction Zone ◽  
Megathrust Earthquakes ◽  
Rupture Model

Origins and Destinations – Social Security Claimant Dynamics

1998 ◽  
Vol 27 (3) ◽  
pp. 351-369 ◽  
Author(s):  
MICHAEL NOBLE ◽  
SIN YI CHEUNG ◽  
GEORGE SMITH
Keyword(s):  
The United States ◽  
Data Sets ◽  
Income Support ◽  
Data Set ◽  
Family Structures ◽  
Highly Educated ◽  
Lone Parents ◽  
Lone Mothers ◽  
Time Period ◽  
Short Time

This article briefly reviews American and British literature on welfare dynamics and examines the concepts of welfare dependency and ‘dependency culture’ with particular reference to lone parents. Using UK benefit data sets, the welfare dynamics of lone mothers are examined to explore the extent to which they inform the debates. Evidence from Housing Benefits data show that even over a relatively short time period, there is significant turnover in the benefits-dependent lone parent population with movement in and out of income support as well as movement into other family structures. Younger lone parents and owner-occupiers tend to leave the data set while older lone parents and council tenants are most likely to stay. Some owner-occupier lone parents may be relatively well off and on income support for a relatively short time between separation and a financial settlement being reached. They may also represent a more highly educated and highly skilled group with easier access to the labour market than renters. Any policy moves paralleling those in the United States to time limit benefit will disproportionately affect older lone parents.

scholarly journals Consistent satellite XCO<sub>2</sub> retrievals from SCIAMACHY and GOSAT using the BESD algorithm

2015 ◽  
Vol 8 (2) ◽  
pp. 1787-1832 ◽  
Author(s):  
J. Heymann ◽  
M. Reuter ◽  
M. Hilker ◽  
M. Buchwitz ◽  
O. Schneising ◽  
...  
Keyword(s):  
Carbon Cycle ◽  
Detailed Comparison ◽  
Mean Difference ◽  
Total Carbon ◽  
Retrieval Algorithm ◽  
Data Sets ◽  
Data Set ◽  
Time Period ◽  
Comparison Results ◽  
The Future

Abstract. Consistent and accurate long-term data sets of global atmospheric concentrations of carbon dioxide (CO2) are required for carbon cycle and climate related research. However, global data sets based on satellite observations may suffer from inconsistencies originating from the use of products derived from different satellites as needed to cover a long enough time period. One reason for inconsistencies can be the use of different retrieval algorithms. We address this potential issue by applying the same algorithm, the Bremen Optimal Estimation DOAS (BESD) algorithm, to different satellite instruments, SCIAMACHY onboard ENVISAT (March 2002–April 2012) and TANSO-FTS onboard GOSAT (launched in January 2009), to retrieve XCO2, the column-averaged dry-air mole fraction of CO2. BESD has been initially developed for SCIAMACHY XCO2 retrievals. Here, we present the first detailed assessment of the new GOSAT BESD XCO2 product. GOSAT BESD XCO2 is a product generated and delivered to the MACC project for assimilation into ECMWF's Integrated Forecasting System (IFS). We describe the modifications of the BESD algorithm needed in order to retrieve XCO2 from GOSAT and present detailed comparisons with ground-based observations of XCO2 from the Total Carbon Column Observing Network (TCCON). We discuss detailed comparison results between all three XCO2 data sets (SCIAMACHY, GOSAT and TCCON). The comparison results demonstrate the good consistency between the SCIAMACHY and the GOSAT XCO2. For example, we found a mean difference for daily averages of −0.60 ± 1.56 ppm (mean difference ± standard deviation) for GOSAT-SCIAMACHY (linear correlation coefficient r = 0.82), −0.34 ± 1.37 ppm (r = 0.86) for GOSAT-TCCON and 0.10 ± 1.79 ppm (r = 0.75) for SCIAMACHY-TCCON. The remaining differences between GOSAT and SCIAMACHY are likely due to non-perfect collocation (±2 h, 10° × 10° around TCCON sites), i.e., the observed air masses are not exactly identical, but likely also due to a still non-perfect BESD retrieval algorithm, which will be continuously improved in the future. Our overarching goal is to generate a satellite-derived XCO2 data set appropriate for climate and carbon cycle research covering the longest possible time period. We therefore also plan to extend the existing SCIAMACHY and GOSAT data set discussed here by using also data from other missions (e.g., OCO-2, GOSAT-2, CarbonSat) in the future.

Sign in / Sign up

Export Citation Format

Share Document