scholarly journals Aftershock sequences of some large earthquakes in the region of Greece

2011 ◽  
Vol 20 (1) ◽  
Author(s):  
PAPAZACHOS B. ◽  
DELIBASIS N. ◽  
LIAPIS N. ◽  
MOUMOULIDIS G. ◽  
PURCARU G.
Keyword(s):  
Aftershock Sequences ◽  
Large Earthquakes ◽  
Of Greece

scholarly journals EARTHQUAKE RELOCATION IN GREECE USING A UNIFIED AND HOMOGENIZED SEISMOLOGICAL CATALOGUE

2017 ◽  
Vol 43 (4) ◽  
pp. 2043 ◽  
Author(s):  
A. Karakonstantis ◽  
P. Papadimitriou
Keyword(s):  
Study Phase ◽  
Single Event ◽  
Earthquake Relocation ◽  
Local Networks ◽  
Aftershock Sequences ◽  
Vertical Location ◽  
Phase Data ◽  
Tectonic Features ◽  
Large Earthquakes ◽  
Of Greece

In this study phase data from the Cornet seismological network installed by the Geophysics-Geothermics Department (University of Athens) and the permanent networks of the Geodynamic Institute of the National Observatory of Athens and of the Geophysics Department of Thessaloniki (Aristotle University), for the decade 1996-2006, were merged. The data were jointly used to relocate the earthquakes that occurred in the broader area of Greece. Initially, single-event algorithms were applied by minimizing spatiotemporal residuals. Following, the hypocenters were relocated using a doubledifference algorithm where rms, as well as the horizontal and vertical location errors (erh, erz) were minimized and a consequence of that better locations were achieved. After that process the spatial distribution of the epicenters outlined major local tectonic features in Greece. Moreover, the same methodology was applied to the aftershock sequences of large earthquakes and the results were successfully compared with those obtained by available local networks that were deployed.

scholarly journals Temporal properties of aftershock sequences of large earthquakes in Iran - Analysis of primary and secondary aftershocks of the Ezgeleh sequence

2020 ◽  
Vol 63 (6) ◽  
Author(s):  
Mahdieh Lavasani ◽  
Elham Shabani
Keyword(s):  
Graphical Method ◽  
Decay Rates ◽  
Iranian Plateau ◽  
Temporal Properties ◽  
Aftershock Sequences ◽  
Decay Parameters ◽  
Large Earthquakes ◽  
Best Fit ◽  
Ezgeleh Earthquake ◽  
Temporal Windows

In this study, the decay of earthquake aftershock sequences of some major earthquakes in different tectonic regimes in the Iranian plateau is discussed. The studied earthquakes are Rigan [2010], Ahar-Varzaghan [2012], Goharan [2013], Sefidsang [2017] and Ezgeleh [2017]. The spatial and temporal windows are considered based on the method proposed by Gardner and Knopoff [1974] to compute decay parameters for each sequence. The decay rates of sequences were compared to well-known models to find the best fit for each sequence. The results showed that the modified Omori is the best fit for Ahar-Varzaghan and Ezgeleh sequences, for Rigan and Sefidsang sequences the modified Omori and the Kisslinger ones found as the best fits. The values of the p parameter of the Reasenberg and Shcherbakov models were larger compared to the Omori model, but the parameter of the Kisslinger model was slightly smaller compared to the Omori one. The c parameter showed an inverse relation to the threshold magnitude. The correlation between the p and c parameters and also the and the Gutenberg and Richter (G-R) parameters were investigated. In addition, we made use of a graphical method to analyze the seismic sequence of the Ezgeleh earthquake during 13 months after the main event. The graphical method was successful to estimate the occurrence of an event with an approximate magnitude of M=6.4 in the sequence.

Background Seismicity before and after the 1976 Ms 7.8 Tangshan Earthquake: Is Its Aftershock Sequence Still Continuing?

2020 ◽  
Author(s):  
Yue Liu ◽  
Jiancang Zhuang ◽  
Changsheng Jiang
Keyword(s):  
Aftershock Sequence ◽  
Tangshan Earthquake ◽  
Aftershock Activity ◽  
Background Rate ◽  
Epidemic Type Aftershock Sequence ◽  
Aftershock Sequences ◽  
Background Seismicity ◽  
Before And After ◽  
Large Earthquakes ◽  
Current Stage

Abstract The aftershock zone of the 1976 Ms 7.8 Tangshan, China, earthquake remains seismically active, experiencing moderate events such as the 5 December 2019 Ms 4.5 Fengnan event. It is still debated whether aftershock sequences following large earthquakes in low-seismicity continental regions can persist for several centuries. To understand the current stage of the Tangshan aftershock sequence, we analyze the sequence record and separate background seismicity from the triggering effect using a finite-source epidemic-type aftershock sequence model. Our results show that the background rate notably decreases after the mainshock. The estimated probability that the most recent 5 December 2019 Ms 4.5 Fengnan District, Tangshan, earthquake is a background event is 50.6%. This indicates that the contemporary seismicity in the Tangshan aftershock zone can be characterized as a transition from aftershock activity to background seismicity. Although the aftershock sequence is still active in the Tangshan region, it is overridden by background seismicity.

scholarly journals Identifying Optimal Intensity Measures for Predicting Damage Potential of Mainshock–Aftershock Sequences

2020 ◽  
Vol 10 (19) ◽  
pp. 6795
Author(s):  
Zhou Zhou ◽  
Xiaohui Yu ◽  
Dagang Lu
Keyword(s):  
Structural Damage ◽  
Damage Index ◽  
Damage Potential ◽  
Earthquake Intensity ◽  
Period Range ◽  
Intensity Measures ◽  
Aftershock Sequences ◽  
Optimal Intensity ◽  
Reasonable Prediction ◽  
Large Earthquakes

Large earthquakes are followed by a sequence of aftershocks. Therefore, a reasonable prediction of damage potential caused by mainshock (MS)–aftershock (AS) sequences is important in seismic risk assessment. This paper comprehensively examines the interdependence between earthquake intensity measures (IMs) and structural damage under MS–AS sequences to identify optimal IMs for predicting the MS–AS damage potential. To do this, four categories of IMs are considered to represent the characteristics of a specific MS–AS sequence, including mainshock IMs, aftershock IMs (i.e., IMMS and IMAS, respectively), and two newly proposed IMs through taking an entire MS–AS sequence as one nominal ground motion (i.e., IM1MS–AS), or determining the ratio of IMAS to IMMS (i.e., IM2MS–AS), respectively. The single-degree-of-freedom systems with varying hysteretic behaviors are subjected to 662 real MS–AS sequences to estimate structural damage in terms the Park–Ang damage index. The intensities in terms of IMMS, IMAS, and IM1MS–AS are correlated with the accumulative damage of structures (i.e., DI1MS–AS). Moreover, the ratio (i.e., DI2MS–AS) of the AS-induced damage increment to the MS-induced damage is related to IM2MS–AS. The results show that IM2MS–AS exhibits significantly better performance than IMMS, IMAS, and IM1MS–AS for predicting the MS–AS damage potential, due to its high interdependence with DI2MS–AS. Among the considered 22 classic IMs, Arias intensity, root-square velocity, and peak ground displacement are respectively the optimal acceleration-, velocity-, and displacement-related IMs to formulate IM2MS–AS. Finally, two empirical equations are proposed to predict the correlations between IM2MS–AS and DI2MS–AS in the entire structural period range.

Earthquake fault plane solutions near Vancouver Island

1979 ◽  
Vol 16 (3) ◽  
pp. 523-531 ◽  
Author(s):  
Garry C. Rogers
Keyword(s):  
Fault Plane ◽  
Vancouver Island ◽  
Nodal Solutions ◽  
Island Region ◽  
Fault Plane Solutions ◽  
Principal Compressive Stress ◽  
Predominant Type ◽  
Shallow Earthquakes ◽  
Aftershock Sequences ◽  
Large Earthquakes

P nodal solutions for six earthquakes in the Vancouver Island region are consistent with a north–south orientation for the principal compressive stress. The predominant type of faulting is strike slip, either dextral slip on northwest striking faults or sinistral slip on northeast striking faults. The few aftershock sequences that can be documented for shallow earthquakes greater than magnitude 5 all contain very few aftershocks, which are small in size. This may indicate that higher than average stress drop is characteristic of large earthquakes in the Vancouver Island region.

Quantifying preparation process of large earthquakes: Damage localization and coalescent dynamics

2020 ◽  
Author(s):  
Ilya Zaliapin ◽  
Yehuda Ben-Zion
Keyword(s):  
Cluster Size ◽  
Southern California ◽  
Time Window ◽  
Oriented Graph ◽  
Seismic Zone ◽  
Average Cluster Size ◽  
Emission Data ◽  
Aftershock Sequences ◽  
Large Earthquakes ◽  
Average Cluster

<p>We attempt to track and quantify preparation processes leading to large earthquakes using two complementary approaches. (a) Localization of brittle deformation manifested by evolving fractional volume with seismic activity, and (b) Coalescence of earthquakes into clusters. We analyze seismicity catalogs from Southern California (SoCal), Parkfield section of the San Andreas Fault (SAF), and region around the 1999 Izmit and Duzce earthquakes in Turkey.</p><p>Localization of deformation is estimated using the Receiver Operating Characteristic (ROC) approach. Specifically, we consider temporal evolution of the fractional volume 0 ≤ V(q) ≤ 1 occupied by the fraction 0 ≤ q ≤ 1 of active voxels with mainshocks. We also consider the localization of the spatial intensity of mainshocks within a sliding time window with respect to the time-averaged distribution, quantified by Gini coefficient G. The significance of the results is assessed using reshuffled catalogs. Analysis within the rupture zones of large earthquakes indicate decrease of V(q) and increase of G (increased localization) prior to the Landers (1992, M7.3), El Mayor-Cucapah (2010, M7.2), Ridgecrest (2019, M7.1), and Duzce (1999, M7.2) mainshocks. We also observe ongoing damage production by the background seismicity around these rupture zones several years before their occurrences. In contrast, we observe increase of V(q) and decrease of G prior to the Parkfield (2004, M6.0) mainshock in the creeping section of the SAF. Next, we examine the quasi-linear region in the Eastern part of Southern California around the Imperial fault, Brawley seismic zone, southern SAF and Eastern California Shear Zone. We document four cycles of background localization, measures by V(q) and G, well aligned in time with the largest events in the region: Landers, Hector Mine, El Mayor-Cucapah, and Ridgecrest. The coalescence process is represented by a time-oriented graph that connects each earthquake in the examined catalog to all earlier earthquakes at the earthquake nearest-neighbor proximity below a specified threshold. We examine the size of the clusters that correspond to low thresholds, and hence represent active clustering episodes. We document increase of the average cluster size prior to the Landers, El Mayor-Cucapah, Ridgecrest and Duzce mainshocks, and decrease of the average cluster size prior to the Parkfield mainshock.</p><p>The results of our complementary localization and coalescent analyses consistently indicate progressive localization of damage prior to the largest earthquakes on non-creeping faults and de-localization on the creeping Parkfield section of SAF. These findings are consistent with analysis of acoustic emission data. The study is a step towards developing methodology for analyzing the dynamics of seismicity in relation to preparation processes of large earthquakes, which is robust to spatio-temporal fluctuations associated with aftershock sequences, data incompleteness and common catalog errors.</p>

Earthquakes without aftershocks: Is there a link to fluid-absent geodynamics?

2020 ◽  
Author(s):  
Thanushika Gunatilake ◽  
Stephen A. Miller
Keyword(s):  
Puerto Rico ◽  
Strong Evidence ◽  
Geodynamic Setting ◽  
Large Magnitude ◽  
Himalayan Orogeny ◽  
Aftershock Sequences ◽  
Deep Fluid ◽  
Global Inventory ◽  
Large Earthquakes ◽  
Fluid Sources

<p>One question that remains unanswered is why some earthquakes are preceded by foreshocks and generate aftershocks by the thousands, while other similarly-sized (or larger) earthquakes produce few, if any, foreshocks or aftershocks. Current understanding equates large magnitude earthquakes with hundreds or even thousands of aftershocks, however a magnitude 7.1 earthquake in Mexico in 2017 and a magnitude 8.0 earthquake in 2019 in Peru generated no foreshocks and no aftershocks (M>4), while the 2020 M6.4 earthquake in Puerto Rico was preceded by ten foreshocks (M>4) and more than sixty aftershocks (M>4) in the first week. The 2019 Ridgecrest earthquake (M7.1) in California was preceded by a M6.4 foreshock and thousands of aftershocks, and this is relevant because this sequence occurred in the fluid-rich Coso hydrothermal/volcanic region. Other examples include the 2001 Kunlun (Tibet) earthquake (M=7.8) that generated a mere 12 aftershocks (M>4) in the first three weeks, while the tectonically similar 2002 Denali earthquake (M=7.9) spawned nearly 160 aftershocks (M>4) in the first three weeks. We attribute this contrasting behaviour to the geodynamic setting; subduction (and thus devolitization) underlies Denali, while a fluid-absent thickened crust (from the Himalayan orogeny) underlies Tibet.</p><p>In this work, we performed a global inventory of large earthquakes and their aftershocks, and find strong evidence that aftershock productivity correlates with the geodynamic and petrological settings hosting the earthquakes. In cases where deep fluid sources are likely (using geodynamic arguments), we find that earthquakes are sometimes preceded by foreshocks, and always produce rich aftershock sequences. On the contrary, using the same geodynamic arguments, we show that regions without an obvious deep fluid source produce few, if any, aftershocks. From this study, we hypothesize that, in general, fluid-absent geodynamic environments generate a dearth of aftershocks, while fluid-rich environments generate aftershock sequences that follow the typical Gutenberg-Richter, Bath and Omori Laws.</p>

Localization and coalescence of seismicity before large earthquakes

2020 ◽  
Vol 223 (1) ◽  
pp. 561-583 ◽  
Author(s):  
Yehuda Ben-Zion ◽  
Ilya Zaliapin
Keyword(s):  
Laboratory Experiments ◽  
San Andreas Fault ◽  
Rock Damage ◽  
Fractional Area ◽  
San Andreas ◽  
Main Shocks ◽  
Aftershock Sequences ◽  
Background Seismicity ◽  
Background Events ◽  
Large Earthquakes

SUMMARY We examine localization processes of low magnitude seismicity in relation to the occurrence of large earthquakes using three complementary analyses: (i) estimated production of rock damage by background events, (ii) evolving occupied fractional area of background seismicity and (iii) progressive coalescence of individual earthquakes into clusters. The different techniques provide information on different time scales and on the spatial extent of weakened damaged regions. Techniques (i) and (ii) use declustered catalogues to avoid the occasional strong fluctuations associated with aftershock sequences, while technique (iii) examines developing clusters in entire catalogue data. We analyse primarily earthquakes around large faults that are locked in the interseismic periods, and examine also as a contrasting example seismicity from the creeping Parkfield section of the San Andreas fault. Results of analysis (i) show that the M > 7 Landers 1992, Hector Mine 1999, El Mayor-Cucapah 2010 and Ridgecrest 2019 main shocks in Southern and Baja California were preceded in the previous decades by generation of rock damage around the eventual rupture zones. Analysis (ii) reveals localization (reduced fractional area) 2–3 yr before these main shocks and before the M > 7 Düzce 1999 earthquake in Turkey. Results with technique (iii) indicate that individual events tend to coalesce rapidly to clusters in the final 1–2 yr before the main shocks. Corresponding analyses of data from the Parkfield region show opposite delocalization patterns and decreasing clustering before the 2004 M6 earthquake. Continuing studies with these techniques, combined with analysis of geodetic data and insights from laboratory experiments and model simulations, might improve the ability to track preparation processes leading to large earthquakes.

scholarly journals PROPERTIES OF FORESHOCKS AND AFTERSHOCKS IN THE AREA OF GREECE

2004 ◽  
Vol 36 (3) ◽  
pp. 1422 ◽  
Author(s):  
M. C. Kourouzidis ◽  
G. F. Karakaisis ◽  
B. C. Papazachos ◽  
C. Makropoulos
Keyword(s):  
Continuous Monitoring ◽  
Surrounding Area ◽  
Fast Determination ◽  
Magnitude Distribution ◽  
Aftershock Sequences ◽  
Power Law Function ◽  
Focal Parameters ◽  
Largest Aftershock ◽  
Of Greece

The results of the study of seismic sequences of all the mainshocks with M>5.6 during 1911-1965 and M>5.0 during 1966-1985 which occurred in the Aegean and surrounding area are presented. As regards the foreshocks, two relations have been proposed that can be used to determine (1) the probability that at least one foreshock, with magnitude Mf or larger, will precede a strong (M>6.0) earthquake, and (2) the probability for the largest foreshock to occur during t days before the mainshock. It was also found that the rate of foreshock occurrence, N(TS), increases as the time of the mainshock approaches and is described by a power-law function. The time and magnitude distribution of several foreshock sequences were also studied. The study of aftershock sequences concerned properties of their largest aftershock, the dependence of the duration and number of the aftershocks on the magnitude of the mainshock and the time and magnitude distribution of several aftershock sequences. The conclusion is that the study of a seismic excitation which is based on continuous monitoring and fast determination of the basic focal parameters of the earthquakes can contribute to clarify whether this activity evolves normally or not.

Localization of seismicity prior to large earthquakes

2021 ◽  
Author(s):  
Ilya Zaliapin ◽  
Yehuda Ben-Zion
Keyword(s):  
Laboratory Experiments ◽  
San Andreas Fault ◽  
Rock Damage ◽  
San Andreas ◽  
Aftershock Sequences ◽  
Background Seismicity ◽  
Seismogenic Faults ◽  
Parkfield Earthquake ◽  
Background Events ◽  
Large Earthquakes

<p>We present results aimed at understanding preparation processes of large earthquakes by tracking progressive localization of earthquake deformation with three complementary analyses: (i) estimated production of rock damage by background events, (ii) spatial localization of background seismicity within damaged areas, and (iii) progressive coalescence of individual earthquakes into clusters. Techniques (i) and (ii) employ declustered catalogs to avoid the occasional strong fluctuations associated with aftershock sequences, while technique (iii) examines developing clusters in entire catalog data. The different techniques provide information on different time scales and on the spatial extent of weakened damaged regions. The analyses reveal generation of earthquake-induced rock damage on a decadal timescale around eventual rupture zones, and progressive localization of background seismicity on a 2-3 yr timescale before several M > 7 earthquakes in southern and Baja California and M7.9 events in Alaska. This is followed by coalescence of earthquakes into growing clusters that precede the mainshocks. Corresponding analysis around the 2004 M6 Parkfield earthquake in the creeping section of the San Andreas fault shows contrasting tendencies to those associated with the large seismogenic faults. The results are consistent with observations from laboratory experiments and physics-based models with heterogeneous materials not dominated by a pre-existing failure zone. Continuing studies with these techniques, combined with analysis of geodetic data and insights from laboratory experiments and model simulations, may allow developing an integrated multi-signal procedure to estimate the approaching time and size of large earthquakes.</p>

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