scholarly journals ETAS Space–Time Modeling of Chile Triggered Seismicity Using Covariates: Some Preliminary Results

2021 ◽  
Vol 11 (19) ◽  
pp. 9143
Author(s):  
Marcello Chiodi ◽  
Orietta Nicolis ◽  
Giada Adelfio ◽  
Nicoletta D’Angelo ◽  
Alex Gonzàlez
Keyword(s):  
Time Scale ◽  
Seismic Activity ◽  
Space Time ◽  
Small Time ◽  
Etas Model ◽  
Related Data ◽  
Triggered Seismicity ◽  
The North ◽  
Time Modeling ◽  
Aftershock Sequences

Chilean seismic activity is one of the strongest in the world. As already shown in previous papers, seismic activity can be usefully described by a space–time branching process, such as the ETAS (Epidemic Type Aftershock Sequences) model, which is a semiparametric model with a large time-scale component for the background seismicity and a small time-scale component for the triggered seismicity. The use of covariates can improve the description of triggered seismicity in the ETAS model, so in this paper, we study the Chilean seismicity separately for the North and South area, using some GPS-related data observed together with ordinary catalog data. Our results show evidence that the use of some covariates can improve the fitting of the ETAS model.

scholarly journals ETAS Space time modelling of Chile induced seismicity using covariates.

2021 ◽  
Author(s):  
Marcello Chiodi ◽  
Orietta Nicolis ◽  
Giada Adelfio ◽  
Nicoletta D'angelo ◽  
Alex Gonzàlez
Keyword(s):  
Time Scale ◽  
Seismic Activity ◽  
Induced Seismicity ◽  
Large Scale ◽  
Space Time ◽  
Expected Number ◽  
Statistical Point ◽  
Linear Predictor ◽  
Etas Model ◽  
Aftershock Sequences

<p>Chilean seismic activity is among the strongest ones in the world. As already shown in previous papers, seismic activity can be usefully described by a space-time branching process, like the ETAS (Epidemic Type Aftershock Sequences) model, which is a semiparametric model with a large time scale component for the background seismicity and a small time scale component for the induced seismicity. The large-scale component intensity function  is usually estimated by  nonparametric techniques, specifically in our paper we used the Forward Likelihood Predictive approach (FLP); the induced seismicity is modelled with a parametric space-time function. In classical ETAS models the expected number of induced events depends only on the magnitude of the main event. From a statistical point of view, forecast of induced seismicity can be performed in the days following a big event; of course the estimation of this component is very important to forecast the evolution, in space and time domain, of a seismic sequence. Together with magnitude, to explain the expected number of induced events we also used other covariates. According to this formulation, the expected number of events induced by event E<sub>i </sub>is a function of a linear predictor η<sub>i</sub>=<strong>x<sub>i</sub></strong><strong>β, </strong>where <strong>x<sub>i </sub></strong>is the vector of covariates observed for the i-th event (the first is usually the magnitude m<sub>i</sub>), and <strong>β</strong> is a vector of parameters to be estimated together with the other parametric and nonparametric components of the ETAS model. We obtained some interesting result using some covariates related to the depth of events and to some GPS measurement, corresponding to earth movement observed before main events. We find that some of these models can improve the description and the forecasting of the induced seismicity in Chile, after a subdivision of the country in different spatial regions. We used open-source software (R package etasFLP) to perform the semiparametric estimation of the ETAS model with covariates.</p>

St. Elias, Alaska, earthquake of February 28, 1979: Tectonic setting and precursory seismic pattern

1980 ◽  
Vol 70 (5) ◽  
pp. 1595-1606
Author(s):  
Omar J. Perez ◽  
Klaus H. Jacob
Keyword(s):  
Seismic Activity ◽  
Main Shock ◽  
Tectonic Setting ◽  
Space Time ◽  
North American Plate ◽  
Rupture Zone ◽  
The North ◽  
The Pacific ◽  
Time Patterns ◽  
Large Earthquakes

abstract The St. Elias earthquake of February 28, 1979 and two earlier earthquakes in the St. Elias Range, Alaska, are shown to have involved thrust motion on gently NNW-dipping faults associated with subduction of the Pacific beneath the North American Plate. The space-time patterns of the seismicity located within and in the immediate vicinity of the rupture zone of the St. Elias event in the 16-yr period prior to it, indicate approximately 6.3 yr of relative quiescence before the main shock, interrupted by a burst of seismic activity about 3 yr prior to the event. This observed seismic pattern resembles those reported for other large earthquakes, and therefore, we suggest that the preceding burst of activity may have been a precursor.

scholarly journals Characteristics of seismic activity before and after the 2018 M6.7 Hokkaido Eastern Iburi earthquake

2019 ◽  
Vol 71 (1) ◽  
Author(s):  
Takao Kumazawa ◽  
Yosihiko Ogata ◽  
Hiroshi Tsuruoka
Keyword(s):  
Seismic Activity ◽  
Main Shock ◽  
Aftershock Sequence ◽  
Aftershock Activity ◽  
Background Rate ◽  
Etas Model ◽  
Epidemic Type Aftershock Sequence ◽  
Aftershock Sequences ◽  
Before And After ◽  
Largest Aftershock

AbstractWe applied the epidemic type aftershock sequence (ETAS) model, the two-stage ETAS model and the non-stationary ETAS model to investigate the detailed features of the series of earthquake occurrences before and after the M6.7 Hokkaido Eastern Iburi earthquake on 6 September 2018, based on earthquake data from October 1997. First, after the 2003 M8.0 Tokachi-Oki earthquake, seismic activity in the Eastern Iburi region reduced relative to the ETAS model. During this period, the depth ranges of the seismicity were migrating towards shallow depths, where a swarm cluster, including a M5.1 earthquake, finally occurred in the deepest part of the range. This swarm activity was well described by the non-stationary ETAS model until the M6.7 main shock. The aftershocks of the M6.7 earthquake obeyed the ETAS model until the M5.8 largest aftershock, except for a period of several days when small, swarm-like activity was found at the southern end of the aftershock region. However, when we focus on the medium and larger aftershocks, we observed quiescence relative to the ETAS model from 8.6 days after the main shock until the M5.8 largest aftershock. For micro-earthquakes, we further studied the separated aftershock sequences in the naturally divided aftershock volumes. We found that the temporal changes in the background rate and triggering coefficient (aftershock productivity) in respective sub-volumes were in contrast with each other. In particular, relative quiescence was seen in the northern deep zones that includes the M5.8 largest aftershock. Furthermore, changes in the b-values of the whole aftershock activity showed an increasing trend with respect to the logarithm of elapsed time during the entire aftershock period, which is ultimately explained by the spatially different characteristics of the aftershocks.

scholarly journals Morphotectonic Analysis along the Northern Margin of Samos Island, Related to the Seismic Activity of October 2020, Aegean Sea, Greece

Geosciences ◽  
2021 ◽  
Vol 11 (2) ◽  
pp. 102
Author(s):  
Paraskevi Nomikou ◽  
Dimitris Evangelidis ◽  
Dimitrios Papanikolaou ◽  
Danai Lampridou ◽  
Dimitris Litsas ◽  
...  
Keyword(s):  
Fault Zone ◽  
Seismic Activity ◽  
Volcanic Rocks ◽  
Active Tectonics ◽  
Normal Fault ◽  
Aegean Sea ◽  
Northern Margin ◽  
The North ◽  
Eastern Aegean ◽  
Half Graben

On 30 October 2020, a strong earthquake of magnitude 7.0 occurred north of Samos Island at the Eastern Aegean Sea, whose earthquake mechanism corresponds to an E-W normal fault dipping to the north. During the aftershock period in December 2020, a hydrographic survey off the northern coastal margin of Samos Island was conducted onboard R/V NAFTILOS. The result was a detailed bathymetric map with 15 m grid interval and 50 m isobaths and a morphological slope map. The morphotectonic analysis showed the E-W fault zone running along the coastal zone with 30–50° of slope, forming a half-graben structure. Numerous landslides and canyons trending N-S, transversal to the main direction of the Samos coastline, are observed between 600 and 100 m water depth. The ENE-WSW oriented western Samos coastline forms the SE margin of the neighboring deeper Ikaria Basin. A hummocky relief was detected at the eastern margin of Samos Basin probably representing volcanic rocks. The active tectonics characterized by N-S extension is very different from the Neogene tectonics of Samos Island characterized by NE-SW compression. The mainshock and most of the aftershocks of the October 2020 seismic activity occur on the prolongation of the north dipping E-W fault zone at about 12 km depth.

scholarly journals The Impact of the North Atlantic Oscillation on Climate through Its Influence on the Atlantic Meridional Overturning Circulation

2016 ◽  
Vol 29 (3) ◽  
pp. 941-962 ◽  
Author(s):  
Thomas L. Delworth ◽  
Fanrong Zeng
Keyword(s):  
North Atlantic ◽  
Time Scale ◽  
Atlantic Meridional Overturning Circulation ◽  
Meridional Overturning Circulation ◽  
The North ◽  
Hemispheric Temperature ◽  
Meridional Overturning ◽  
The North Atlantic Oscillation ◽  
The Impact ◽  
Model Ocean

Abstract The impact of the North Atlantic Oscillation (NAO) on the Atlantic meridional overturning circulation (AMOC) and large-scale climate is assessed using simulations with three different climate models. Perturbation experiments are conducted in which a pattern of anomalous heat flux corresponding to the NAO is added to the model ocean. Differences between the perturbation experiments and a control illustrate how the model ocean and climate system respond to the NAO. A positive phase of the NAO strengthens the AMOC by extracting heat from the subpolar gyre, thereby increasing deep-water formation, horizontal density gradients, and the AMOC. The flux forcings have the spatial structure of the observed NAO, but the amplitude of the forcing varies in time with distinct periods varying from 2 to 100 yr. The response of the AMOC to NAO variations is small at short time scales but increases up to the dominant time scale of internal AMOC variability (20–30 yr for the models used). The amplitude of the AMOC response, as well as associated oceanic heat transport, is approximately constant as the time scale of the forcing is increased further. In contrast, the response of other properties, such as hemispheric temperature or Arctic sea ice, continues to increase as the time scale of the forcing becomes progressively longer. The larger response is associated with the time integral of the anomalous oceanic heat transport at longer time scales, combined with an increased impact of radiative feedback processes. It is shown that NAO fluctuations, similar in amplitude to those observed over the last century, can modulate hemispheric temperature by several tenths of a degree.

Seasonal trends of reservoir-triggered seismicity in Song Tranh 2 reservoir, Vietnam

2021 ◽  
Author(s):  
Grzegorz Lizurek ◽  
Konstantinos Leptokaropoulos ◽  
Jan Wiszniowski ◽  
Izabela Nowaczyńska ◽  
Nguyen Van Giang ◽  
...  
Keyword(s):  
Water Level ◽  
Pore Pressure ◽  
Seismic Activity ◽  
Water Level Fluctuations ◽  
Response Type ◽  
Seasonal Trends ◽  
Triggered Seismicity ◽  
Stress Orientation ◽  
Water Level Changes ◽  
Pressure Changes

<p>Reservoir-triggered seismicity (RTS) is the longest known anthropogenic seismicity type. It has the potential to generate seismic events of M6 and bigger. Previous studies of this phenomenon have proved that major events are triggered on preexisting major discontinuities, forced to slip by stress changes induced by water level fluctuations and/or pore-pressure changes in the rock mass in the vicinity of reservoirs. Song Tranh 2 is an artificial water reservoir located in Central Vietnam. Its main goal is back up the water for hydropower plant. High seismic activity has been observed in this area since the reservoir was first filled in 2011. The relation between water level and seismic activity in the Song Tranh area is complex, and the lack of clear correlation between water level and seismic activity has led to the conclusion that ongoing STR2 seismic activity is an example of the delayed response type of RTS. However, the first phase of the activity observed after impoundment has been deemed a rapid response type. In this work, we proved that the seismicity recorded between 2013 and 2016 manifested seasonal trends related to water level changes during wet and dry seasons. The response of activity and its delay with respect to water level changes suggest that the main triggering factor is pore pressure change due to the significant water level changes observed. A stress orientation difference between low and high water periods is also revealed. The findings indicate that water load and related pore pressure changes influence seismic activity and stress orientation in this area.</p><p>This work was partially supported by research project no. 2017/27/B/ST10/01267, funded by the National Science Centre, Poland, under agreement no. UMO-2017/27/B/ST10/01267.</p>

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