scholarly journals An Evaluation on the Behaviors of Aftershock Sequence of November 26th, 2019 Earthquake, ML=6.3, North of Durrës, Albania

2021 ◽  
Author(s):  
Serkan ÖZTÜRK ◽  
Rrapo ORMENI
Keyword(s):  
Aftershock Sequence

The Norris Lake Earthquake Swarm of June Through September, 1993; Preliminary Findings

1994 ◽  
Vol 65 (2) ◽  
pp. 167-171 ◽  
Author(s):  
L.T. Long ◽  
A. Kocaoglu ◽  
R. Hawman ◽  
P.J.W. Gore
Keyword(s):  
Earthquake Swarm ◽  
Building Stone ◽  
Aftershock Sequence ◽  
Average Depth ◽  
Induced Earthquakes ◽  
Epicentral Area ◽  
Event Recorder ◽  
Significant Damage ◽  
The 1950S ◽  
Recreational Lake

Abstract During the summer of 1993, the residents in the Norris Lake community, Lithonia, Georgia, were bothered by an incessant swarm of earthquakes. The largest, a magnitude 2.7 on September 23, showed a normal aftershock decay and occurred after the main swarm. Over 10,000 earthquakes have been detected, of which perhaps 500 were felt. The earthquakes began June 8, 1993, with a 5-day swarm. The residents, accustomed to quarry explosions, suspected the quarries of irregular activities. To locate the source of the events, a visual recorder and a digital event recorder were placed in the epicentral area. Ten to 20 events were detected per day for the next three weeks. The swarm then escalated to a peak of over 100 per day by August 15, 1993. Activity following the peak died down to about 10 events per day. The magnitude 2.7 event of September 23 was followed by a normal aftershock sequence. The larger events were felt with intensity V within 2 km of their epicenter, and noticed (intensity II) to a distance of 15 km. Some incidents of cracked wallboard and foundations have been reported, but no significant damage has been documented. Preliminary locations, based on data from digital event recorders, suggest an average depth of 1.0 km. The hypocenters are in the Lithonia gneiss, a massive migmatite resistant to weathering and used locally as a building stone. The epicenters are 1 to 2 km south-southwest of the Norris Lake Community. The cause of the seismicity is not yet known. The earthquakes are characteristic of reservoir-induced earthquakes; however, Norris Lake is a small (96 acres), 2 to 5m deep recreational lake which has existed since the 1950s.

scholarly journals Seismicity, focal mechanism, and stress tensor analysis of the Simav region, western Turkey

2020 ◽  
Vol 12 (1) ◽  
pp. 479-490
Author(s):  
Ahu Kömeç Mutlu
Keyword(s):  
Moment Tensor ◽  
Aftershock Sequence ◽  
Movement Direction ◽  
Normal Faults ◽  
Normal Faulting ◽  
Stress Inversion ◽  
Western Turkey ◽  
Stress Orientations ◽  
Extension Direction ◽  
Inversion Analysis

AbstractThis study focuses on the seismicity and stress inversion analysis of the Simav region in western Turkey. The latest moderate-size earthquake was recorded on May 19, 2011 (Mw 5.9), with a dense aftershock sequence of more than 5,000 earthquakes in 6 months. Between 2004 and 2018, data from earthquake events with magnitudes greater than 0.7 were compiled from 86 seismic stations. The source mechanism of 54 earthquakes with moment magnitudes greater than 3.5 was derived by using a moment tensor inversion. Normal faults with oblique-slip motions are dominant being compatible with the NE-SW extension direction of western Turkey. The regional stress field is assessed from focal mechanisms. Vertically oriented maximum compressional stress (σ1) is consistent with the extensional regime in the region. The σ1 and σ3 stress axes suggest the WNW-ESE compression and the NNE-SSW dilatation. The principal stress orientations support the movement direction of the NE-SW extension consistent with the mainly observed normal faulting motions.

Aftershock sequence of the 9 May 1989 Canary Islands earthquake

1996 ◽  
Vol 255 (1-2) ◽  
pp. 157-162 ◽  
Author(s):  
M.J. Jiménez ◽  
M. García-Fernández
Keyword(s):  
Canary Islands ◽  
Aftershock Sequence

scholarly journals Intermediate-term forecasting of aftershocks from an early aftershock sequence: Bayesian and ensemble forecasting approaches

2015 ◽  
Vol 120 (4) ◽  
pp. 2561-2578 ◽  
Author(s):  
Takahiro Omi ◽  
Yosihiko Ogata ◽  
Yoshito Hirata ◽  
Kazuyuki Aihara
Keyword(s):  
Aftershock Sequence ◽  
Ensemble Forecasting

The San Salvador Earthquake of October 10, 1986—Seismological Aspects and Other Recent Local Seismicity

1987 ◽  
Vol 3 (3) ◽  
pp. 419-434 ◽  
Author(s):  
Randall A. White ◽  
David H. Harlow ◽  
Salvador Alvarez
Keyword(s):  
Main Shock ◽  
Fault Plane ◽  
Vertical Plane ◽  
Aftershock Sequence ◽  
Central American ◽  
Fault Plane Solution ◽  
San Salvador ◽  
The North ◽  
Volcanic Chain ◽  
Plane Solution

The San Salvador earthquake of October 10, 1986 originated along the Central American volcanic chain within the upper crust of the Caribbean Plate. Results from a local seismograph network show a tectonic style main shock-aftershock sequence, with a magnitude, Mw, 5.6. The hypocenter was located 7.3 km below the south edge of San Salvador. The main shock ruptured along a nearly vertical plane toward the north-northeast. A main shock fault-plane solution shows a nearly vertical fault plane striking N32\sz\E, with left-lateral sense of motion. This earthquake is the second Central American volcanic chain earthquake documented with left-lateral slip on a fault perpendicular to the volcanic chain. During the 2 1/2 years preceeding the earthquake, minor microseismicity was noted near the epicenter, but we show that this has been common along the volcanic chain since at least 1953. San Salvador was previously damaged by a volcanic chain earthquake on May 3, 1965. The locations of six foreshocks preceding the 1965 shock show a distinctly WNW-trending distribution. This observation, together with the distribution of damage and a fault-plane solution, suggest that right-lateral slip occurred along a fault sub-parallel with Central American volcanic chain. We believe this is the first time such motion has been documented along the volcanic chain. This earthquake was also unusual in that it was preceded by a foreshock sequence more energetic than the aftershock sequence. Earlier this century, on June 08, 1917, an Ms 6.4 earthquake occurred 30 to 40 km west of San Salvador Volcano. Only 30 minutes later, an Ms 6.3 earthquake occurred, centered at the volcano, and about 35 minutes later the volcano erupted. In 1919 an Ms 6 earthquake occurred, centered at about the epicenter of the 1986 earthquake. We conclude that the volcanic chain is seismically very active with variable styles of seismicity.

The Ceres, South Africa, earthquake of September 29, 1969

1971 ◽  
Vol 61 (4) ◽  
pp. 851-859 ◽  
Author(s):  
R. W. E. Green ◽  
S. Bloch
Keyword(s):  
South Africa ◽  
Fault Plane ◽  
Large Earthquake ◽  
Aftershock Sequence ◽  
Fault System ◽  
Vertical Fault ◽  
Seismic Recording ◽  
The Republic ◽  
Aftershock Region ◽  
Considerable Damage

abstract Aftershocks following the Ceres earthquake of September 29, 1969, (Magnitude 6.3) were monitored using a number of portable seismic recording stations. Earthquakes of this magnitude are rare in South Africa. The event occurred in a relatively densely-populated part of the Republic, and resulted in nine deaths and considerable damage. Accurate locations of some 125 aftershocks delineate a linear, almost vertical fault plane. The volume of the aftershock region is 3 × 9 × 20 km3 with the depth of the aftershocks varying from surface to 9 km. Aftershocks following the September event had almost ceased when another large earthquake (Magnitude 5.7) occurred on April 14, 1970. Following this event, the frequency and magnitude of aftershocks increased, and they were located on a limited portion of the same fault system delineated by the September 29th aftershocks. Previously-mapped faults do not correlate simply with the fault zone indicated by the aftershock sequence.

Earthquake clusters expected from bare statistics: How bursts and swarms emerge from exogenous and epidemic aftershock processes.

2021 ◽  
Author(s):  
Jordi Baro
Keyword(s):  
Heat Flow ◽  
Solid Earth ◽  
Point Process ◽  
Branching Process ◽  
Aftershock Sequence ◽  
Statistical Properties ◽  
Etas Model ◽  
Stress Changes ◽  
Earthquake Clusters ◽  
Statistical Laws

<p>Earthquake catalogs exhibit strong spatio-temporal correlations. As such, earthquakes are often classified into clusters of correlated activity. Clusters themselves are traditionally classified in two different kinds: (i) bursts, with a clear hierarchical structure between a single strong mainshock, preceded by a few foreshocks and followed by a power-law decaying aftershock sequence, and (ii) swarms, exhibiting a non-trivial activity rate that cannot be reduced to such a simple hierarchy between events. </p><p>The Epidemic Aftershock Sequence (ETAS) model is a linear Hawkes point process able to reproduce earthquake clusters from empirical statistical laws [Ogata, 1998]. Although not always explicit, the ETAS model is often interpreted as the outcome of a background activity driven by external forces and a Galton-Watson branching process with one-to-one causal links between events [Saichev et al., 2005]. Declustering techniques based on field observations [Baiesi & Paczuski, 2004] can be used to infer the most likely causal links between events in a cluster. Following this method, Zaliapin and Ben‐Zion (2013) determined the statistical properties of earthquake clusters characterizing bursts and swarms, finding a relationship between the predominant cluster-class and the heat flow in seismic regions.</p><p>Here, I show how the statistical properties of clusters are related to the fundamental statistics of the underlying seismogenic process, modeled in two point-process paradigms [Baró, 2020].</p><p>The classification of clusters into bursts and swarms appears naturally in the standard ETAS model with homogeneous rates and are determined by the average branching ratio (nb) and the ratio between exponents α and b characterizing the production of aftershocks and the distribution of magnitudes, respectively. The scale-free ETAS model, equivalent to the BASS model [Turcotte, et al., 2007], and usual in cold active tectonic regions, is imposed by α=b and reproduces bursts. In contrast, by imposing α<0.5b, we recover the properties of swarms, characteristic of regions with high heat flow. </p><p>Alternatively, the same declustering methodology applied to a non-homogeneous Poisson process with a non-factorizable intensity, i.e. in absence of causal links, recovers swarms with α=0, i.e. a Poisson Galton-Watson process, with similar statistical properties to the ETAS model in the regime α<0.5b.</p><p>Therefore, while bursts are likely to represent actual causal links between events, swarms can either denote causal links with low α/b ratio or variations of the background rate caused by exogenous processes introducing local and transient stress changes. Furthermore, the redundancy in the statistical laws can be used to test the hypotheses posed by the ETAS model as a memory‐less branching process. </p><p>References:</p><ul><li> <p>Baiesi, M., & Paczuski, M. (2004). <em>Physical Review E</em>, 69, 66,106. doi:10.1103/PhysRevE.69.066106.</p> </li> <li> <p>Baró, J. (2020).  <em>Journal of Geophysical Research: Solid Earth,</em> 125, e2019JB018530. doi:10.1029/2019JB018530.</p> </li> <li> <p>Ogata, Y. (1998) <em>Annals of the Institute of Statistical Mathematics,</em> 50(2), 379–402. doi:10.1023/A:1003403601725.</p> </li> <li> <p>Saichev, A., Helmstetter, A. & Sornette, D. (2005) <em>Pure appl. geophys.</em> 162, 1113–1134. doi:10.1007/s00024-004-2663-6.</p> </li> <li> <p>Turcotte, D. L., Holliday, J. R., and Rundle, J. B. (2007), <em>Geophys. Res. Lett.</em>, 34, L12303, doi:10.1029/2007GL029696.</p> </li> <li> <p>Zaliapin, I., and Ben‐Zion, Y. (2013), <em>J. Geophys. Res. Solid Earth</em>, 118, 2865– 2877, doi:10.1002/jgrb.50178.</p> </li> </ul>

Earthquake migration in the Fairbanks, Alaska seismic zone

1980 ◽  
Vol 70 (1) ◽  
pp. 223-241
Author(s):  
Larry Gedney ◽  
Steve Estes ◽  
Nirendra Biswas
Keyword(s):  
B Value ◽  
Aftershock Sequence ◽  
Stress Axis ◽  
Seismic Zone ◽  
Epicentral Area ◽  
Focal Mechanism Solutions ◽  
Relative Stress ◽  
Earthquake Migration ◽  
Dislocation Process ◽  
High Level

abstract Since a series of moderate earthquakes near Fairbanks, Alaska in 1967, the “Fairbanks seismic zone” has maintained a consistently high level of seismicity interspersed with sporadic earthquake swarms. Five swarms occurring since 1970 demonstrate that tightly compacted centers of activity have tended to migrate away from the epicentral area of the 1967 earthquakes. Comparative b-coefficients of the first four swarms indicate that they occurred under different relative stress conditions than the last episode, which exhibited a higher b-value and was, in fact, a main shock of magnitude 4.6 with a rapidly decaying aftershock sequence. This last recorded sequence in February 1979 was an extension to greater depths along a lineal seismic zone whose first recorded activation occurred during a swarm two years earlier. Focal mechanism solutions indicate a north-south orientation of the greatest principal stress axis, σ1, in the area. A dislocation process related to crustal spreading between strands of a right-lateral fault, similar to that which has been inferred for southern California, is suggested.

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