Spatio-temporal variations of source parameters in the nucleation zone of the 6 April 2009, Mw 6.1 L'Aquila Earthquake

Mapping Intimacies ◽

10.5194/egusphere-egu2020-22596 ◽

2020 ◽

Author(s):

Rita Di Giovambattista ◽

Giovanna Calderoni ◽

Antonio Rovelli

Keyword(s):

Stress Drop ◽

Main Shock ◽

Source Parameters ◽

Dynamic Strength ◽

Temporal Variations ◽

Apparent Stress ◽

L’Aquila Earthquake ◽

Focal Volume ◽

Spatio Temporal ◽

The Individual

<p>We present the results of Brune stress drop (&#8710;&#963;) and apparent stress (&#964;a) variability of &#160;earthquakes located in a small zone adjacent to the hypocenter of the damaging Mw 6.1 L'Aquila earthquake. Their magnitude ranges between &#160;2.7 and 4.1. Interevent variability of stress drop and apparent stress results in a factor of 10, well beyond the individual&#8208;event uncertainty. Radiation efficiency &#951;sw = &#964;a/&#8710;&#963; varies mostly between 0.1 and 0.2, but decreases in the days immediately before and after the main shock to values as low as 0.06. This may be related to the migration of the events occurring in those days into a focal volume with higher dynamic strength. The temporal change of &#951;sw might be interpreted as a spatial variation due to the earthquake migration into the locked portion of the fault originating the main shock. Furthermore, no variation in stress drop and apparent stress can be observed between foreshocks and aftershocks but the smallest and largest &#8710;&#963; result in a good correlation with the largest and smallest b&#8208;values respectively, as already documented in literature in the rupture nucleation volume of large earthquakes.</p>

Download Full-text

Improved approach for stress drop estimation and its application to an induced earthquake sequence in Oklahoma

Geophysical Journal International ◽

10.1093/gji/ggaa316 ◽

2020 ◽

Vol 223 (1) ◽

pp. 233-253

Author(s):

X Chen ◽

R E Abercrombie

Keyword(s):

Stress Drop ◽

Source Parameters ◽

High Stress ◽

Temporal Variations ◽

Earthquake Source ◽

Average Stress ◽

Corner Frequency ◽

Resolution Limit ◽

Spectral Fitting ◽

Spatio Temporal

SUMMARY We calculate source parameters for fluid-injection induced earthquakes near Guthrie, Oklahoma, guided by synthetic tests to quantify uncertainties. The average stress drop during an earthquake is a parameter fundamental to ground motion prediction and earthquake source physics, but it has proved hard to measure accurately. This has limited our understanding of earthquake rupture, as well as the spatio-temporal variations of fault strength. We use synthetic tests based on a joint spectral-fitting method to define the resolution limit of the corner frequency as a function of the maximum frequency of usable signal, for both individual spectra and the average from multiple stations. Synthetic tests based on stacking analysis find that an improved stacking approach can recover the true input stress drop if the corner frequencies are within the resolution limit defined by joint spectral-fitting. We apply the improved approach to the Guthrie sequence, using different wave types and signal-to-noise criteria to understand the stability of the calculated stress drop values. The results suggest no systematic scaling relationship of stress drop for M ≤ 3.1 earthquakes, but larger events (M ≥ 3.5) tend to have higher average stress drops. Some robust spatio-temporal variations can be linked to the triggering processes and indicate possible stress heterogeneity within the fault zone. Tight clustering of low stress drop events at the beginning stage of the sequence suggests that pore pressure influences earthquake source processes. Events at shallow depth have lower stress drop compared to deeper events. The largest earthquake occurred within a cluster of high stress drop events, likely rupturing a strong asperity.

Download Full-text

Source mechanism and surface-wave attenuation studies for Tibet earthquake of July 14, 1973

Bulletin of the Seismological Society of America ◽

10.1785/bssa0690030737 ◽

1979 ◽

Vol 69 (3) ◽

pp. 737-750

Author(s):

D. D. Singh ◽

Harsh K. Gupta

Keyword(s):

Surface Wave ◽

Stress Drop ◽

Wave Attenuation ◽

Source Parameters ◽

High Stress ◽

The Body ◽

P Wave ◽

Slip Angle ◽

Apparent Stress ◽

Crust And Upper Mantle

abstract Focal mechanism for Tibet earthquake of July 14, 1973 (M = 6.9, mb = 6.0) has been determined using the P-wave first motions, S-wave polarization angles, and surface-wave spectral data. A normal faulting is obtained with a plane having strike N3°W, dip 51°W, and slip angle 81°. The source parameters have been estimated for this event using the body- and surface-wave spectra. The seismic moment, fault length, apparent stress, stress drop, seismic energy release, average dislocation, and fault area are estimated to be 2.96 × 1026 dyne-cm, 27.4 km, 14 bars, 51 bars, 1.4 × 1022 ergs, 157 cm, and 628 km2, respectively. The high stress drop and apparent stress associated with this earthquake indicate that the high stresses are prevailing in this region. The specific quality factor Q is found to vary from 21 to 1162 and 22 to 1110 for Rayleigh and Love waves, respectively. These wide ranges of variation in the attenuation data may be due to the presence of heterogeneity in the crust and upper mantle.

Download Full-text

Person Re-Identification by Discriminative Local Features of Overlapping Stripes

Symmetry ◽

10.3390/sym12040647 ◽

2020 ◽

Vol 12 (4) ◽

pp. 647

Author(s):

Fawad ◽

Muhammad Jamil Khan ◽

MuhibUr Rahman

Keyword(s):

Feature Extraction ◽

Surveillance System ◽

Local Features ◽

Temporal Variations ◽

Visual Surveillance ◽

Local Patch ◽

Robust Feature Extraction ◽

Spatio Temporal ◽

The Individual ◽

Extraction Model

The human visual system can recognize a person based on his physical appearance, even if extreme spatio-temporal variations exist. However, the surveillance system deployed so far fails to re-identify the individual when it travels through the non-overlapping camera’s field-of-view. Person re-identification (Re-ID) is the task of associating individuals across disjoint camera views. In this paper, we propose a robust feature extraction model named Discriminative Local Features of Overlapping Stripes (DLFOS) that can associate corresponding actual individuals in the disjoint visual surveillance system. The proposed DLFOS model accumulates the discriminative features from the local patch of each overlapping strip of the pedestrian appearance. The concatenation of histogram of oriented gradients, Gaussian of color, and the magnitude operator of CJLBP bring robustness in the final feature vector. The experimental results show that our proposed feature extraction model achieves rank@1 matching rate of 47.18% on VIPeR, 64.4% on CAVIAR4REID, and 62.68% on Market1501, outperforming the recently reported models from the literature and validating the advantage of the proposed model.

Download Full-text

Spatio-temporal Evolution of Wet-dry Event Features and their Transition across Upper Jhelum Basin (UJB)-South Asia

10.5194/nhess-2021-267 ◽

2021 ◽

Author(s):

Rubina Ansari ◽

Giovanna Grossi

Keyword(s):

South Asia ◽

Temporal Evolution ◽

Southern Oscillation ◽

Temporal Variations ◽

Mitigation Measures ◽

Before And After ◽

Droughts And Floods ◽

Rapid Transition ◽

Spatio Temporal ◽

The Individual

Abstract. The increasing rate of extreme events (Droughts and floods) and their rapid transition magnifies the associated socio-economic impacts than the individual event. Understanding of spatio-temporal evolution of wet-dry events collectively, their characteristics and transition (wet to dry and dry to wet) is therefore significant to identify and locate most vulnerable hotspots, providing the basis for the adaptation and mitigation measures. The Upper Jhelum Basin (UJB)-South Asia was selected as a case study, where the relevance of wet-dry events and their transition have not been assessed yet, despite of clear evidence of climate change in the region. The Standardized Precipitation Evapotranspiration Index (SPEI) at the monthly time scale was applied to detect and characterize wet and dry events for the period 1981–2014. The results of temporal variations of SPEI showed a strong change in basin climatic features associated with El Niño Southern Oscillation (ENSO) at the end of 1997, with the prevalence of wet and dry events before and after 1997 respectively. The results of spatial analysis show a higher susceptibility of the monsoon-dominated region towards wet events, with more intense events occurring in the eastern part, whereas a higher severity and duration is featuring in the southwestern part of the basin. In contrast, westerlies-dominated region was found to be the hotspot of dry events with higher duration, severity, and intensity. Moreover, the surrounding region of the Himalaya divide line and the monsoon-dominated part of the basin were found to be the hotspots of rapid wet-dry transition events.

Download Full-text

Stress Drop, Apparent Stress, and Radiation Efficiency of Clustered Earthquakes in the Nucleation Volume of the 6 April 2009, M w 6.1 L'Aquila Earthquake

Journal of Geophysical Research Solid Earth ◽

10.1029/2019jb017513 ◽

2019 ◽

Vol 124 (10) ◽

pp. 10360-10375

Author(s):

Giovanna Calderoni ◽

Antonio Rovelli ◽

Rita Di Giovambattista

Keyword(s):

Stress Drop ◽

Radiation Efficiency ◽

Apparent Stress ◽

L’Aquila Earthquake

Download Full-text

A global spatially Continuous Solar Induced Fluorescence (CSIF) dataset using neural networks

10.5194/bg-2018-255 ◽

2018 ◽

Cited By ~ 3

Author(s):

Yao Zhang ◽

Joanna Joiner ◽

Seyed Hamed Alemohammad ◽

Sha Zhou ◽

Pierre Gentine

Keyword(s):

Primary Production ◽

Vegetation Index ◽

Normalized Difference Vegetation Index ◽

Gross Primary Production ◽

Terrestrial Ecosystems ◽

Temporal Variations ◽

Clear Sky ◽

Spatio Temporal ◽

The Individual ◽

Sky Conditions

Abstract. Satellite-retrieved Solar Induced Chlorophyll Fluorescence (SIF) has shown great potential to monitor the photosynthetic activity of terrestrial ecosystems. However, several issues, including low spatial and temporal resolution of the gridded datasets and high uncertainty of the individual retrievals, limit the applications of SIF. In addition, inconsistency in measurements footprints also hinder the direct comparison between gross primary production (GPP) from eddy covariance (EC) flux towers and satellite-retrieved SIF. In this study, by training a neural network (NN) with surface reflectance from the MODerate-resolution Imaging Spectroradiometer (MODIS) and SIF from Orbiting Carbon Observatory-2 (OCO-2), we generated two global spatially continuous SIF (CSIF) datasets at moderate spatio-temporal resolutions (0.05 degree 4-day) during 2001–2016, one for clear-sky conditions and the other one in all-sky conditions. The clear-sky instantaneous CSIF (CSIFclear-inst) shows high accuracy against the clear-sky OCO-2 SIF and little bias across biome types. The all-sky daily average CSIF (CSIFall-daily) dataset exhibits strong spatial, seasonal and interannual dynamics that are consistent with daily SIF from OCO-2 and the Global Ozone Monitoring Experiment-2 (GOME-2). An increasing trend (0.39 %) of annual average CSIFall-daily is also found, confirming the greening of Earth in most regions. Since the difference between satellite observed SIF and CSIF is mostly caused by the environmental down-regulation on SIFyield, the ratio between OCO-2 SIF and CSIFclear-inst can be an effective indicator of drought stress that is more sensitive than normalized difference vegetation index and enhanced vegetation index. By comparing CSIFall-daily with gross primary production (GPP) estimates from 40 EC flux towers across the globe, we find a large cross-site variation (c.v. = 0.36) of GPP-SIF relationship with the highest regression slopes for evergreen needleleaf forest. However, the cross-biome variation is relatively limited (c.v. = 0.15). These two continuous SIF datasets and the derived GPP-SIF relationship enable a better understanding of the spatial and temporal variations of the GPP across biomes and climate.

Download Full-text

SPECTRAL and SOURCE PARAMETERS of CRIMEAN-BLACK SEA EARTHQUAKES

Zemletriaseniia Severnoi Evrazii [Earthquakes in Northern Eurasia] ◽

10.35540/1818-6254.2020.23.25 ◽

2020 ◽

pp. 250-262

Author(s):

B. Pustovitenko ◽

E. Eredzhepov

Keyword(s):

Black Sea ◽

Stress Drop ◽

Seismic Waves ◽

Source Parameters ◽

Normal Component ◽

Strike Slip ◽

The Black Sea ◽

Dislocation Model ◽

Tensile Forces ◽

The Individual

The spectral and dynamic source parameters (М0, r0, , , ησ, , ū, Eu and Mw) of 13 Crimean earthquakes with КП = 7.2–11.2 (Mw=2.6–4.1), restored by 123 amplitude spectra of longitudinal and transverse seismic waves recorded by digital regional seismic stations is shown. Approximation of the spectra and the source dynamic parameters calculation based on their parameters is performed in the framework of the Brune dislocation model. Four to seven station definitions participated in the averaging of focal parameters, which ensured a small standard deviation, the scattering degree index of the individual estimates. The best convergence of the station definitions is obtained for the radius of a circular dislocation. The highest values of dynamic para-meters have been obtained for the perceptible earthquake on March 2 with КП=11.2, and the lowest values have been obtained for its weak aftershock on April 6 with КП = 7.2. Within the total range of energies the value of the stress drop does not exceed = 106Pa(10 bar), and the apparent stress drop does not exceed ησ<3∙105Pa (3 bar). The average values of seismic moments and circular dislocation radius within the errors of their deter-mination match the average long-term correlations of the parameters on the earthquake energy level obtained by the analog recording.For the strongest earthquakes on March 2 with Mwreg=4.1 and October 18 with Mwreg=3.8 solutions of the focal mechanisms were obtained. The March 2 earthquake occurred in the central part of the region near the South Coast of Crimea under the action of horizontal tensile forces oriented near the latitude. The type of movement in the focus is a obligue slip with predominance of a normal component over a strike-slip. The earthquake on October 18 occurred in the central part of the Black Sea basin in condition of sublatitudinal compression and submeridional extension. Type of movement in the source is a pure strike-slip. For the main shock on March 2 and its six aftershocks, energy spectra according to the data of Alushta station and their main parameters are given. The analysis of obtained results is given.

Download Full-text