Investigating the earthquake catalog of the National Observatory of Athens

Chouliaras, G.

doi:10.5194/nhess-9-905-2009

Cited by 27 publications

(23 citation statements)

References 29 publications

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“…It is well established that the homogeneity of an earthquake catalogue and the respective magnitude of completeness versus time play a key role in the assessment of the seismic hazard. Periods of detection increase due to seismological station expansions throughout the instrumental period and the addition of the Kozani (NOA) seismological station in 1994 should be considered as artificial or man-made rate changes (Chouliaras and Stavtrakakis, 1997;Chouliaras, 2009). In the present study, the epicenters and source parameters are obtained from the catalogue of Makropoulos et al (2012), an updated earthquake catalogue for Greece and adjacent areas, covering the time span 1900-2009.…”

Section: Data and Analysismentioning

confidence: 99%

Seismic hazard assessment in Polyphyto Dam area (NW Greece) and its relation with the "unexpected" earthquake of 13 May 1995 (Ms = 6.5, NW Greece)

Pavlou

Κaviris

Chousianitis

et al. 2013

Nat. Hazards Earth Syst. Sci.

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Abstract. Seismic hazard assessment and seismicity changes are investigated in the Kozani-Grevena area, at the western margin of internal Hellenides in NW Greece. The region is of great interest, since it was characterized by very low seismic activity until 1995, when the "unexpected" Kozani-Grevena earthquake (M s = 6.5) occurred. This event is of significant importance for Greece, since it, along with the 1999 Athens earthquake, initiated the modification of the Greek Building Code. In order to detect any seismicity changes, the seismicity of the region was divided into three time windows: the first up to 1973, the second from 1900 to 1994 and the third covering the entire instrumental period.For the above mentioned time windows, seismic hazard assessment was performed using the extreme values method. The results indicate an increase of the peak ground acceleration (PGA) values after the impoundment, with the exception of the area in the vicinity of the NE edge of the Dam. Before the occurrence of the 1995 event, the epicentral region also exhibited higher PGA values than before the impoundment. The most significant increase in PGA values is observed SE of the Polyphyto artificial lake, where the largest values are observed for the second and the third period. The coincident increase in the number of earthquakes and in the PGA values may be attributed to the impoundment of the Polyphyto Dam.The maximum expected magnitude is calculated by the extreme values method and Gumbel's third asymptotic distribution. The results reveal similar values of maximum expected magnitudes (M max = 6.5), independent of the seismicity rate, indicating that the 13 May 1995 earthquake was not an "unexpected" event, since the magnitude of an oncoming earthquake depends mainly on the tectonics of the region and the characteristics of the active faults.

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Section: Data and Analysismentioning

confidence: 99%

Seismic hazard assessment in Polyphyto Dam area (NW Greece) and its relation with the "unexpected" earthquake of 13 May 1995 (Ms = 6.5, NW Greece)

Pavlou

Κaviris

Chousianitis

et al. 2013

Nat. Hazards Earth Syst. Sci.

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“…In short, the GENAS application describes the important variations in the number of earthquakes larger and smaller than a given magnitude versus time. GENAS algorithm defines the times which stand out as the start of periods were increases and/or decreases of earthquake activity can be identified as well as the magnitude range affected by these variations (Zúñiga et al, 2000;Chouliaras, 2009). Results of the GENAS model show the important breaks in slope which begin from the end of data for all magnitude groups.…”

Section: Results Of Statistical Investigations Of Recent Seismicity Amentioning

confidence: 99%

“…Here, "mag and below" states all earthquakes having a magnitude lower than M -value D ________________________ __ and, "mag and above" refers all event having a magnitude greater than M -value. The GENAS method hypothesized that D only independent earthquakes can be compared in order to avoid false alarms from seismicity rate changes due to foreshock and aftershock sequences or clusters (Chouliaras, 2009). For this reason, we used the declustered earthquake catalogue for GENAS analysis.…”

Section: Results Of Statistical Investigations Of Recent Seismicity Amentioning

confidence: 99%

Spatial and temporal analysis of recent seismicity in different parts of the Vlora-Lushnja-Elbasani-Dibra Transversal Fault Zone, Albania

Ormeni¹,

Öztürk²,

Fundo³

et al. 2018

AJES

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Spatial and temporal evaluation of current seismic activity throughout the Vlora-Lushnja-Elbasani-Dibra (VLED) transversal fault zone were carried out at the beginning of year 2016. The seismotectonic b-value, fractal dimension Dc-value and precursory seismic quiescence Z-value are considered for a detailed statistical analysis. Completeness magnitude Mc-value varies from 2.5 to 2.7 for different parts of the VLED fault zone. The b-value is calculated as 1.10±0.04 for the south western part and 1.13±0.05 for the middle part, whereas it is estimated as 0.94±0.07 for the north eastern part of the study region. These results reveal that b-values for all regions are well represented by a b-value typically close to 1.0. There are clear decreasing trends in temporal changes of b-values before the occurrences of some strong main shocks. On the contrary, no earthquakes are observed in some periods after decrease of b-value. Dc-values are computed as 2.66±0.04 for the south western part, 2.64±0.03 for the middle part and 2.15±0.02 for the north eastern part of the VLED fault zone. These rather large values show that earthquake activity is more clustered at larger scales or in smaller areas in the study area.Considering the phenomenon of seismic quiescence as a precursor of the main earthquakes gives successful outcomes in defining the potential anomalies and possible locations of future earthquakes. Quiescence analysis of current seismicity at the beginning of 2016 in the VLED fault zone is performed with the test of standard normal deviate Z-value. Distributions of resulting Z-values show six anomalous regions along the different parts of the VLED fault zone. These quiescence areas are detected at (i) 40.81ºN-19.86ºE (including Kuc-Bubullim, southeast of Lushnja town), (ii) 41.00ºN-20.01ºE (in the Cerriku, south of Elbasani town), (iii) 41.31ºN-20.13ºE (around Bene-Qafe, northeast of Elbasani town), (iv) 41.43ºN-20.21ºE (Krasta-Batra, south of Bulqiza town), (v) 41.28ºN-20.49ºE (including Carrishta-Stebleve, northeast of Librazhdi town), (vi) 41.51ºN-20.51ºE (including Qerrenec-Gjorica, west of Dibra town). As an important result, analyses of spatial and temporal characteristics of the earthquake activity may supply significant clues for revealing the future seismic hazard along the VLED fault zone, and these anomaly regions may be interpreted as the locations of next possible earthquakes.

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“…3 shows the time evolution of the cumulative seismicity for this region. A power law increase in the reported seismicity is observed in general with the NOA seismicity catalogue, due to the expansion of the seismological network and the improvement in detecting seismic events in recent years (Chouliaras, 2009). The sudden increases in the seismicity for the Santorini region are due to the occurrence of seismicity swarms and also due to the seismic sequence of the largest recent earthquake on 26 June 2009 with a magnitude M L = 5 to the NE of Thera island along the Columbo fault line.…”

Section: Data Analysis and Resultsmentioning

confidence: 99%

Recent seismicity detection increase in the Santorini volcanic island complex

Chouliaras

Δρακάτος

Μακροπουλοσ

et al. 2012

Nat. Hazards Earth Syst. Sci.

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Abstract. Santorini is the most active volcanic complex in the South Aegean Volcanic Arc. To improve the seismological network detectability of the seismicity in this region, the Institute of Geodynamics of the National Observatory of Athens (NOA) recently installed 4 portable seismological stations supplementary to the 3 permanent stations operating in the region. The addition of these stations has significantly improved the detectability and reporting of the local seismic activity in the NOA instrumental seismicity catalogue. In this study we analyze quantitatively the seismicity of the Santorini volcanic complex. The results indicate a recent significant reporting increase mainly for events of small magnitude and an increase in the seismicity rate by more than 100%. The mapping of the statistical significance of the rate change with the z-value method reveals that the rate increase exists primarily in the active fault zone perpendicular to the extensional tectonic stress regime that characterizes this region. The spatial distribution of the b-value around the volcanic complex indicates a low b-value distribution parallel to the extensional stress field, while the b-value cross section of the volcanic complex indicates relatively high b-values under the caldera and a significant b-value decrease with depth. These results are found to be in general agreement with the results from other volcanic regions and they encourage further investigations concerning the seismic and volcanic hazard and risk estimates for the Santorini volcanic complex using the NOA earthquake catalogue.

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Investigating the earthquake catalog of the National Observatory of Athens

Cited by 27 publications

References 29 publications

Seismic hazard assessment in Polyphyto Dam area (NW Greece) and its relation with the "unexpected" earthquake of 13 May 1995 (<i>M</i><sub>s</sub> = 6.5, NW Greece)

Seismic hazard assessment in Polyphyto Dam area (NW Greece) and its relation with the "unexpected" earthquake of 13 May 1995 (<i>M</i><sub>s</sub> = 6.5, NW Greece)

Spatial and temporal analysis of recent seismicity in different parts of the Vlora-Lushnja-Elbasani-Dibra Transversal Fault Zone, Albania

Recent seismicity detection increase in the Santorini volcanic island complex

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Investigating the earthquake catalog of the National Observatory of Athens

Cited by 27 publications

References 29 publications

Seismic hazard assessment in Polyphyto Dam area (NW Greece) and its relation with the &quot;unexpected&quot; earthquake of 13 May 1995 (&lt;i&gt;M&lt;/i&gt;&lt;sub&gt;s&lt;/sub&gt; = 6.5, NW Greece)

Seismic hazard assessment in Polyphyto Dam area (NW Greece) and its relation with the &quot;unexpected&quot; earthquake of 13 May 1995 (&lt;i&gt;M&lt;/i&gt;&lt;sub&gt;s&lt;/sub&gt; = 6.5, NW Greece)

Spatial and temporal analysis of recent seismicity in different parts of the Vlora-Lushnja-Elbasani-Dibra Transversal Fault Zone, Albania

Recent seismicity detection increase in the Santorini volcanic island complex

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Seismic hazard assessment in Polyphyto Dam area (NW Greece) and its relation with the "unexpected" earthquake of 13 May 1995 (<i>M</i><sub>s</sub> = 6.5, NW Greece)

Seismic hazard assessment in Polyphyto Dam area (NW Greece) and its relation with the "unexpected" earthquake of 13 May 1995 (<i>M</i><sub>s</sub> = 6.5, NW Greece)