scholarly journals Earthquake clusters in NW Peloponnese.

2016 ◽  
Vol 47 (3) ◽  
pp. 1167
Author(s):  
M. Mesimeri ◽  
E. Papadimitriou ◽  
V. Karakostas ◽  
G. Tsaklidis
Keyword(s):  
Spatial Distribution ◽  
Main Shock ◽  
B Value ◽  
Earthquake Swarms ◽  
Background Rate ◽  
Seismicity Rate ◽  
Seismic Moment Release ◽  
Earthquake Clusters ◽  
Stress Accumulation ◽  
Skewness And Kurtosis

Clusters commonly occur as main shock – aftershock (MS-AS) sequences but also as earthquake swarms, which are empirically defined as an increase in seismicity rate above the background rate without a clear main shock. A delcustering algorithm is employed to identify clusters from a complete catalog of earthquakes that occurred in the area of NW Peloponnese (Greece) during 1980-2007. In order to distinguish these clusters we calculate the skewness and kurtosis of seismic moment release for each cluster, since swarm-like sequences generally have lower skew value of moment release history than MS-AS. The spatial distribution of b-value was calculated for the entire catalog as for the declustered one, in order to correlate them with seismicity behavior of the region. Finally, the pre-stress field of Achaia 2008 earthquake was calculated aiming to associate the stress accumulation with the occurrence of the identified clusters

Coda Q before the 1983 Hawaii (MS = 6.6) earthquake

1988 ◽  
Vol 78 (3) ◽  
pp. 1279-1296
Author(s):  
Zhong-Xian Huang ◽  
Max Wyss
Keyword(s):  
Unit Volume ◽  
Main Shock ◽  
B Value ◽  
Rectangular Region ◽  
S Wave ◽  
Coda Q ◽  
Seismicity Rate ◽  
High Q ◽  
Source Mechanisms ◽  
Q Values

Abstract Coda Q values were derived for more than 300 microearthquakes that occurred in a 6-yr period before the 16 November 1983 Kaoiki, Hawaii, earthquake (MS = 6.6). The sources were located within a 14 × 16 km rectangular region surrounding the main shock epicenter, and most of them occurred at depths between 5 and 10 km. Digital recordings from three stations at epicentral distances ranging from 0 to 18 km were used. Coda Q was calculated from the amplitude decay rate of the S-wave coda in nine frequency bands from 4.5 to 27 Hz. The average Q of the NW part of the studied area is about 15 per cent higher than that of the SE part. These two subregions also showed differences in seismicity, b value, and microearthquake source mechanisms. In the high-Q volume, the b value was 1.0, and the rate of earthquakes per unit volume was about 50 per cent of the rate in the low-Q volume where b = 1.3. One interpretation of these observations is that more extensive faulting in the SE Kaoiki fault zone leads to lower Q, higher b value, and a higher seismicity rate. During the 5 to 6 yr before the mainshock, the 1-yr average Q values were stable. No significant Q change could be identified as a precursor to the main shock.

Rampart seismic zone of central Alaska

1983 ◽  
Vol 73 (3) ◽  
pp. 813-829
Author(s):  
P. Yi-Fa Huang ◽  
N. N. Biswas
Keyword(s):  
Main Shock ◽  
Fault Plane ◽  
B Value ◽  
Aftershock Sequence ◽  
Strike Slip ◽  
Lithospheric Plate ◽  
Normal Faults ◽  
Seismic Zone ◽  
The West ◽  
Fault Plane Solutions

abstract This paper describes the characteristics of the Rampart seismic zone by means of the aftershock sequence of the Rampart earthquake (ML = 6.8) which occurred in central Alaska on 29 October 1968. The magnitudes of the aftershocks ranged from about 1.6 to 4.4 which yielded a b value of 0.96 ± 0.09. The locations of the aftershocks outline a NNE-SSW trending aftershock zone about 50 km long which coincides with the offset of the Kaltag fault from the Victoria Creek fault. The rupture zone dips steeply (≈80°) to the west and extends from the surface to a depth of about 10 km. Fault plane solutions for a group of selected aftershocks, which occurred over a period of 22 days after the main shock, show simultaneous occurrences of strike-slip and normal faults. A comparison of the trends in seismicity between the neighboring areas shows that the Rampart seismic zone lies outside the area of underthrusting of the lithospheric plate in southcentral and central Alaska. The seismic zone outlined by the aftershock sequence appears to represent the formation of an intraplate fracture caused by regional northwest compression.

Observations of the Coyote Lake, California earthquake sequence of August 6, 1979

1980 ◽  
Vol 70 (2) ◽  
pp. 559-570 ◽  
Author(s):  
R. A. Uhrhammer
Keyword(s):  
San Francisco ◽  
Fault Zone ◽  
Strong Earthquake ◽  
Main Shock ◽  
B Value ◽  
Aftershock Sequence ◽  
The South ◽  
The North ◽  
Temporal And Spatial Characteristics ◽  
Largest Aftershock

abstract At 1705 UTC on August 6, 1979, a strong earthquake (ML = 5.9) occurred along the Calaveras fault zone south of Coyote Lake about 110 km southeast of San Francisco. This strong earthquake had an aftershock sequence of 31 events (2.4 ≦ ML ≦ 4.4) during August 1979. No foreshocks (ML ≧ 1.5) were observed in the 3 months prior to the main shock. The local magnitude (ML = 5.9) and the seismic moment (Mo = 6 × 1024 dyne-cm from the SH pulse) for the main shock were determined from the 100 × torsion and 3-component ultra-long period seismographs located at Berkeley. Local magnitudes are determined for the aftershocks from the maximum trace amplitudes on the Wood-Anderson torsion seismograms recorded at Berkeley (Δ ≊ 110 km). Temporal and spatial characteristics of the aftershock sequence are presented and discussed. Some key observations are: (1) the first six aftershocks (ML ≧ 2.4) proceed along the fault zone progressively to the south of the main shock; (2) all of the aftershocks (ML ≧ 2.4) to the south of the largest aftershock (ML = 4.4) have a different focal mechanism than the aftershocks to the north; (3) no aftershocks (ML ≧ 2.4) were observed significantly to the north of the main shock for the first 5 days of the sequence; and (4) the b-value (0.70 ± 0.17) for the aftershock sequence is not significantly different from the average b-value (0.88 ± 0.08) calculated for the Calaveras fault zone from 16 yr of data.

Seismic characteristics of southeast Missouri as indicated by a regional telemetered microearthquake array

1976 ◽  
Vol 66 (6) ◽  
pp. 1953-1964 ◽  
Author(s):  
William Stauder ◽  
Mark Kramer ◽  
Gerard Fischer ◽  
Stephen Schaefer ◽  
Sean T. Morrissey
Keyword(s):  
Spatial Distribution ◽  
Active Faults ◽  
B Value ◽  
New Madrid Seismic Zone ◽  
Seismic Zone ◽  
Mississippi Embayment ◽  
Linear Dimensions ◽  
Seismic Characteristics ◽  
Active Zones ◽  
First Time

abstract A regional microearthquake network has been established in the New Madrid seismic zone to study better the seismic characteristics of this region. The network consists of 16 stations distributed on the borders of and within the head of the Mississippi embayment. The network has a location sensitivity for all earthquakes of mb ≧ 1 occurring within the network. A total of 330 earthquakes has been located within a 1.5° by 1.5° area inside the array during the first 21 months of operation. The spatial distribution of these hypocenters has identified for the first time in this region the existence of linear seismically active zones, corresponding presumably to seismically active faults. Several of these trend N40°E, parallel to the axis of the embayment. Others trend NW; these latter are parallel to and possibly are related to the crest of the Pascola arch which joins the Ozark uplift to the Nashville dome. The linear dimensions of the features identified thus far vary in length from about 25 km to about 100 km. The b value as determined by the number of earthquakes located thus far is about 0.8.

Microearthquake activity following the Parkfield, California earthquake of June, 1966

1969 ◽  
Vol 59 (2) ◽  
pp. 603-613
Author(s):  
Thomas J. Fitch
Keyword(s):  
Main Shock ◽  
High Sensitivity ◽  
Amplitude Distribution ◽  
B Value ◽  
Epicentral Area ◽  
San Andreas ◽  
Recording Station ◽  
Parkfield Earthquake ◽  
Secondary Aftershock ◽  
Secondary Fault

abstract A high sensitivity microearthquake recording station was established 10 km from the epicenter of the magnitude 5.5 Parkfield earthquake of June 28, 1966. Beginning 43 hours after the main shock, an hourly average of 22 microaftershocks was recorded for a period of 13 days. Events with magnitudes roughly equivalent to a Richter magnitude of −1.5 were recorded. The amplitude distribution suggests that there was a smaller percentage of small shocks in the Parkfield microaftershock series than has commonly been reported for Japanese and other California aftershock series. b values between 0.8 and 0.9 are commonly reported while the average b value for the Parkfield microaftershock series was 0.59. The distribution of S-P times for the microaftershocks is consistent with the epicentral area defined in other studies as a strip approximately 5 km wide astride a 35 km long trace of the San Andreas fault; however, some evidence suggests that the microaftershock activity extends beyond the zone defined by the larger aftershocks. The spatial distribution of microearthquake activity is shown to be strongly non-uniform within the aftershock zone. The microaftershocks, in general, did not cluster in time about the larger aftershocks (M > 2.0). Of 24 aftershocks with M greater than or equal to 2.0, only one event gave strong evidence of triggering a secondary aftershock series. Assuming that secondary foreshock and/or aftershock series imply the creation or reactivation of a secondary fault, one is led to the conclusion that secondary faulting was a rare occurrence in the Parkfield aftershock zone.

Nowcasting and multifractal features of the seismicity in the subduction zone of Tehuantepec Isthmus, southern México

2021 ◽  
Author(s):  
Alejandro Ramírez-Rojas ◽  
Elsa Leticia Flores-Márquez
Keyword(s):  
Main Shock ◽  
B Value ◽  
Fluctuation Analysis ◽  
Southern Mexico ◽  
Multifractal Detrended Fluctuation Analysis ◽  
Middle America Trench ◽  
Seismicity Distribution ◽  
Isthmus Of Tehuantepec ◽  
Temporal Rate ◽  
Detrended Fluctuation

<p>After the M8.2 earthquake occurred on September 07, 2017 at Isthmus of Tehuantepec, notable spatial and temporal changes where<br>registered, the temporal rate of occurrence increased and the spatial seismicity distribution showed a clear clusterization along<br>the region of collision of the Tehuantepec Transform/Ridge with the Middle America Trench off Chiapas. Also, the b-value in the<br>Gutenberg-Richer law showed changes in time. On the basis of that behavior we studied the sequence of magnitudes of the<br>earthquakes occurred within the Isthmus of Tehuantepec at southern Mexico from 2010 to 2020, by using the nowcasting method<br>and the multifractal detrended fluctuation analysis. Our findings suggest the b-value could depend on time and after the main-shock<br>M8.2, the underlying dynamics in the Tehuantepec ridge has been changed, which is clearly described by our analyses based on<br>nowcasting method and in the multifractality estimated changes.</p>

Risk from Oklahoma’s Induced Earthquakes: The Cost of Declustering

2020 ◽  
Author(s):  
Jeremy Maurer ◽  
Deborah Kane ◽  
Marleen Nyst ◽  
Jessica Velasquez
Keyword(s):  
Financial Risk ◽  
B Value ◽  
Earthquake Risk ◽  
Eastern United States ◽  
Induced Earthquakes ◽  
Magnitude Distribution ◽  
Seismicity Rate ◽  
Seismicity Rates ◽  
Tectonic Earthquakes ◽  
Frequency Magnitude

ABSTRACT The U.S. Geological Survey (USGS) has for each year 2016–2018 released a one-year seismic hazard map for the central and eastern United States (CEUS) to address the problem of induced and triggered seismicity (ITS) in the region. ITS in areas with historically low rates of earthquakes provides both challenges and opportunities to learn about crustal conditions, but few scientific studies have considered the financial risk implications of damage caused by ITS. We directly address this issue by modeling earthquake risk in the CEUS using the 1 yr hazard model from the USGS and the RiskLink software package developed by Risk Management Solutions, Inc. We explore the sensitivity of risk to declustering and b-value, and consider whether declustering methods developed for tectonic earthquakes are suitable for ITS. In particular, the Gardner and Knopoff (1974) declustering algorithm has been used in every USGS hazard forecast, including the recent 1 yr forecasts, but leads to the counterintuitive result that earthquake risk in Oklahoma is at its highest level in 2018, even though there were one-fifth as many earthquakes as occurred in 2016. Our analysis shows that this is a result of (1) the peculiar characteristics of the declustering algorithm with space-varying and time-varying seismicity rates, (2) the fact that the frequency–magnitude distribution of earthquakes in Oklahoma is not well described by a single b-value, and (3) at later times, seismicity is more spatially diffuse and seismicity rate increases are closer to more populated areas. ITS in Oklahoma may include a combination of swarm-like events with tectonic-style events, which have different frequency–magnitude and aftershock distributions. New algorithms for hazard estimation need to be developed to account for these unique characteristics of ITS.

scholarly journals Investigating the earthquake catalog of the National Observatory of Athens

2009 ◽  
Vol 9 (3) ◽  
pp. 905-912 ◽  
Author(s):  
G. Chouliaras
Keyword(s):  
B Value ◽  
Spatial And Temporal Variability ◽  
Earthquake Catalog ◽  
National Observatory ◽  
Data Set ◽  
Seismicity Rate ◽  
Earthquake Prediction Research ◽  
The Times ◽  
Seismicity Rate Changes ◽  
Selection Of

Abstract. The earthquake catalog of the National Observatory of Athens (NOA) since the beginning of the Greek National Seismological Network development in 1964, is compiled and analyzed in this study. The b-value and the spatial and temporal variability of the magnitude of completeness of the catalog is determined together with the times of significant seismicity rate changes. It is well known that man made inhomogeneities and artifacts exist in earthquake catalogs that are produced by changing seismological networks and in this study the chronological order of periods of network expansion, instrumental upgrades and practice and procedures changes at NOA are reported. The earthquake catalog of NOA is the most detailed data set available for the Greek area and the results of this study may be employed for the selection of trustworthy parts of the data in earthquake prediction research.

Seismotectonics of the northern Longitudinal Valley, Taiwan, inferred from aftershock sequences of 2018 Mw6.4 and 2019 Mw6.2 Hualien earthquakes

2020 ◽  
Author(s):  
Wei-Fang Sun ◽  
Hao Kuo-Chen ◽  
Zhuo-Kang Guan ◽  
Wen-Yen Chang
Keyword(s):  
Main Shock ◽  
Surface Deformation ◽  
Plate Boundary ◽  
Aftershock Sequence ◽  
Tectonic Structures ◽  
Seismicity Rate ◽  
Transitional Area ◽  
Main Shocks ◽  
Aftershock Sequences ◽  
Seismic Networks

<p>In the Hualien area, two Mw6.4 and Mw6.2 earthquakes, 20 km apart, occurred in February 2018 and April 2019 respectively. The former to the northeast, located offshore to ​​the Liwu river, triggered several earthquake clusters along the Milun fault and southward to the Longitudinal Valley, the suture of the Eurasian and the Philippine Sea plates; the latter to the southwest, located in the Central Range, also triggered several seismic swarms in the Central Range,  along the Liwu river to the northeast and at Ji'an to the southeast. Except for the Milun fault, neither GPS nor InSAR observations detects significant surface deformation after the occurrence of these two main shocks, indicating that the earthquake ruptures mainly developed within the crust. Therefore, seismic observation becomes an efficient tool for revealing the seismotectonics of the two earthquake sequences. For monitoring the aftershock sequences, two days after the main shocks, we deployed two geophone arrays, 70 Z-component RefTek 125A TEXANs for two weeks in 2018 and 47 three-component Fairfield Nodal Z-Lands for one month in 2019, with 1-5 km station spacing around the Hualien City. These earthquake swarms were well recorded and analyzed through the dense seismic networks. The numbers of aftershock sequences manually identified are two-fold more than that issued by the Central Weather Bureau, Taiwan. The seismicity of the 2018 aftershock sequence, to depths of between 5-15 km, was significantly reduced within 10 days after the main shock. however, the seismicity of the 2019 aftershock sequence, to depths of between 2-50 km, was still above background seismicity rate 30 days after the main shock. The spatial distribution of the 2018 aftershock sequence could be related to a fault zone of the plate boundary, but that of the 2019 and the relocated 1986 aftershock sequences show a conjugate thrust fault pair beneath the eastern Central Range. Our results clearly depict several local tectonic structures that have not been observed at the northern tip of the Longitudinal Valley, not only a suture but also a transitional area from collision to subduction.</p>

scholarly journals Characteristics of the catalogue according to the KNET network (Northern Tian Shan)

2021 ◽  
Vol 254 ◽  
pp. 02005
Author(s):  
Naylya Sycheva ◽  
Vladimir Sychev
Keyword(s):  
Distribution Function ◽  
Spatial Distribution ◽  
Statistical Analysis ◽  
Energy Distribution ◽  
Representative Sample ◽  
B Value ◽  
Statistical Characteristics ◽  
S Waves ◽  
Localization Errors ◽  
Minimum Number

Various characteristics of the catalogue obtained from the data of the KNET network, containing the parameters of more than 10,000 earthquakes that occurred from 1994 to 2020, are considered. A statistical analysis of the number of P- and S-waves registered by each station of the network is carried out. The activity of the stations during the localization of earthquakes has been determined. The most active station is AAK. The minimum number of P- and S-waves is recorded at the ULHL station. Statistical analysis of localization errors has been performed. The boundaries of the territory for which the minimum values of errors are observed are determined. The statistical characteristics of earthquakes in terms of magnitude, time, depth are presented. The distribution of the number of earthquakes by different energy classes in time and the spatial distribution of earthquakes by depths: 0-5 km, 5-10 km, 10-15 km and more than 15 km are constructed. The Gutenberg Richter law was used to describe the energy distribution function of earthquakes. A representative sample of the catalogue was determined, which includes events with M ≥ 1.8. The b-value for the directory is 0.88.

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