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RETAS model - Restricted Epidemic Type Aftershock Sequence model. 

The stochastic model was developed by Gospodinov and Rotondi (2006) and it is based on the idea that only aftersocks stronger than some magnitude threshold Mth can trigger secondary aftershock activity (on the figure above this threshold is 4.5). Thus, by  changing the threshold Mth from the magnitude cut-off  Mo to the main shock magnitude Mmain, RETAS chooses the best fit stochastic model for the temporal behavior of the sequences among a number of models including the MOF and the ETAS models as limit cases. 

 

 

Site effect assessment using H/V spectral ratio technique -

 

 

the H/V spectral ratio method is an experimental technique to evaluate some characteristics of soft-sedimentary (soil) deposits. Due to its low-cost both for the survey and analysis, the H/V technique has been frequently adopted in seismic microzonation investigations. 

The method has proven to be useful to estimate the fundamental period of soil deposits. However, measurements and the analysis should be performed with caution. The main recommended application of the H/V technique in microzonation studies is to map the fundamental period of the site and help constrain the geological and geotechnical models used for numerical computations (a map of the fumdamental frequency for the town of Jambol - SE Bulgaria). 

This technique is most effective in estimating the natural frequency of soft soil sites when there is a large impedance contrast with the underlying bedrock. The method is especially recommended in areas of low and moderate seismicity, due to the lack of significant earthquake recordings, as compared to high seismicity areas.

The technique was applied to seisic noise records from the towns of Plovdiv (Kandilarov, Atakan, Havskov and Gospodinov, 2009) and Jambol in Bulgaria and from Bergen, Norway. The results are being prepared for publication.

 

 

Fractal Properties analysis

The application of fractal distribution analysis has some specific aspects. It is usually difficult to present an adequate interpretation of the obtained values of fractal coefficients for earthquake epicenter or hypocenter distributions. That is why we aim at other goals – to verify how a fractal coefficient depends on different spatial distributions (Gospodinov, Marekova, Marinov, 2009).

We simulate earthquake spatial data by generating randomly points first in a 3D space - cube, then in a parallelepiped, diminishing one of its sides. We then continue this procedure in 2D and 1D space. For each simulated data set we calculate the points’ fractal coefficient (correlation fractal dimension of epicenters) and then check for correlation between the coefficients values and the type of spatial distribution.
In that way one can obtain a set of standard fractal coefficients’ values for varying spatial distributions. These then can be used when real earthquake data is analyzed by comparing the real data coefficients values to the standard fractal coefficients. Such an approach can help in interpreting the fractal analysis results through different types of spatial distributions.

 

Recent projects

2009 - 2010, ŠŃ09-ŌŌ-011/15.04.2009, Plovdiv University "Paisiy Hilendarski", "Study of seismic hazard features by stochastic modeling and ambient noise analysis" (coordinator - Dragomir Gospodinov)

2006 - 2008, Project BG-9/2005 (bilateral BG-Greece (“Aristotle University”) -  Bulgaria (GFI) cooperation) on “Seismogenesis and interactions between earthquake sources in the Southern Balkans” (continuation; coordinator - Dragomir Gospodinov)

2006 - 2007, Risk analysis by MAHB and NEDIES - action 4332 of EC-DG-JRC (coodinator - Boyko Ranguelov)

2006 - Project with TIG-DVO, RAN-Russia “Seismotectonics and properties of the strong earthquake sources”, (coodinator - Boyko Ranguelov)

2005 - Site effect assessment using H/V spectral ratio and Standard Spectral Ratio methods in the 'Old Town' area of Plovdiv city - Bulgaria, project with the Institute of Solid Earth Physics - University of Bergen, Norway (coodinator - Dragomir Gospodinov)

 

 

Research partners we keep active cooperation with:

 

- Prof. Eleftheria Papadimitriou and Prof. Vassilios Karakostas - Department of Geophysics, School of Geology at the "Ariatotle' University in Thessaloniki, Greece

 

- Dr. Renata Rotondi - Consiglio Nazionale delle Ricerche Istituto di Matematica Applicata e Tecnologie Informatiche (IMATI), (Milano Department), Italy

 

- Alexander Kandilarov and Prof. K. Atakan - Bergen University, Norway

 

- Associate Professor Boyko Ranguelov - National Instituteof Geophysics, Geodesy and Geography

 

- Dr. Galina Lyamikina - Tihookeanskij institut geofiziki (TIG-DVO), RAN-Russia

  • Recent  publications

    • Gospodinov, D. and Rotondi,  R., (2001), Exploratory analysis of marked Poisson Processes applied to Balkan earthquake sequences, Journ. Balkan Geoph. Soc., 4, 3, 61-68.

    Gospodinov, D., V. Karakostas, R. Papadimitriou, (2005), Stochastic modelling of the relaxation process after the M=9.0 Sumatra earthquake of December 26, 2004; preliminary analysis, Proc. of the  4th Con. of the Balkan Geoph. Society, 9-12 October 2005, Bucharest, Romania, pp.327-330

    Gospodinov, D., B. Ranguelov, E. Papadimitriou, V. Karakostas, (2005), Statistical methods to analyze seismicity interaction in neighbor zones; application to simulated data, Proc. of the 80-years Anniv.Intern. Sci.Conference on Geology, Sofia, November 17-18, 2005, pp.185-188

    Gospodinov D. and Rotondi R., (2006),  "RETAS: a restricted ETAS model inspired, by Bath's law", The 4th Internat.Workshop on Statistical Seismology, The Graduate University for Advanced Studies, Shonan Village, Japan, 9-13 January 2006, ISM (Institute of Statistical Mathematics) Report on Research and Eucation No. 23, 92-95. 

    Gospodinov, D., R. Rotondi,(2006), Statistical Analysis of Triggered Seismicity in the Kresna Region of SW Bulgaria (1904) and the Umbria-Marche Region of Central Italy (1997), Pure appl. geophys., 163, 1597–1615

    Tranos M., Karakostas V., Papadimitriou E., Kachev V., Ranguelov B., Gospodinov D., (2006), Major active faults of SW Bulgaria: implications of their geometry, kinematics and the regional active stress regime., in Tectonic development of the Eastern Mediterranean region. (Robertson A. and Mountrakis D. - eds.), Geological Society of London, Special publications 260, pp. 671-687.

    Karaksotas V., Papadimitriou E., Gospodinov D., Ranguelov B., (2006), Slip distribution for the 1928 Chirpan and Plovdiv main shocks and earthquake triggering., Proc. Intl.Conf. SGEM 2006 - papers., Albena, 12-16 June., vol. 2, p.119-126.

    B. Ranguelov, S. Dimitrova, D. Gospodinov, G. Lamykina, (2007). Geodynamics of the South Balkans -    Seismotectonic Model, Fractality and Nonlinear Properties., in Monograph GEODYNAMICS OF THE BALKAN PENINSULA (Ed.G.Milev), Reports of Geodesy, No. 5 (80), pp. 609 – 626.

    Papadimitriou E., V. Karakostas, M. Tranos, B. Ranguelov, D. Gospodinov., (2007). Static stress changes associated   with normal faulting earthquakes in South Balkan area., Int. J. Earth Sci. (Geol. Rundsch.), Springer-Verlag,  Volume 96, Number 5, pp. 911-924, DOI: 10.1007/s00531-006-0139-x

    Gospodinov D., Ranguelov B., Papadimitriou E. and Karakostas V., (2007), Exploratory Application of a Compound Poisson Process to Model Aftershock Energy Release after the Denali Fault M7.9 earthquake, November 3, 2002., Proc. 17th Intl. Symp. Geodesy’07, Sofia , 8-9.Nov. šp. 303-313.

    Gospodinov D., Ranguelov B., Karakosttas V., Papadimitriou E., Tanev A., Kandilarov A., (2007). Preliminary results on the implementration of the H/V spectral ratio technique on ambient vibrations in the town of Jambol. , Ext. abstr. Nat.Conf. Geosciences’07., December 13-14, 2007 , Sofia , 127-128 pp.

    Marekova E., Ranguelov B. and Gospodinov D., (2007). Statistical Investigations of earthquake sequences on different regions of the world., accepted for public. In Proc. Nat.Conf. Geosciences’07., December 13-14, 2007 , Sofia

    Gospodinov D., Karakostas, Papadimitriou E., Ranguelov B., (2007), Analysis of relaxation temporal patterns in Greece through the RETAS model approach.,  Physics of the Earth and Planetary Interiors (PEPI), Vol 165/3-4, pp 158-175, DOI information: 10.1016/j.pepi.2007.09.001

    Kandilarov A., Atakan K., Havskov J., Gospodinov D. (2009) An investigation of the significance of local site effects in Plovdiv, Bulgaria, Bulletin of Earthquake Engineering. 7, 181-198, DOI 10.1007/s10518-008-9091

    Ranguelov B., G. Alexiev, D.Gospodinov., (2009), Natural Hazards Cartography in Bulgaria – a European perspective. Proc. 19th Intl. Symp. Geodesy 09., Sofia, 5-6 Nov. 2009, pp. 260-266. ISBN: 978-80-87159-07

    Gospodinov D., E. Marekova ,  A. Marinov, (2009), Verifying the Dependence of Fractal Coefficients on Different Spatial Distributions, AIP, 2010, AIP Conference Proceedings, 1, 731-736, DOI: 10.1063/1.3322545, http://link.aip.org/link/?APC/1203/731/1

    Gospodinov D., Papadimitriou E. and Karakostas V., Ranguelov B, (2009), Energy release patterns in aftershock sequences of North Aegean Sea (Greece) through stochastic modelling, Cashiers du Centre Europeen de Geodynamique et de Seimologie, Vol.28. p. 141-146

    Astiopoulos, A.C., Papadimitriou, E., Karakostas, V., Gospodinov, D., Drakatos, G., (2010), Seismicity changes detection during the seismic sequences evolution as evidence of stress changes, Proc. 12th International Congress of the Geological Society of Greece, May 19-20, 2010, Thessaloniki, Greece, p. 1994-2004

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