Snježana Markušić

Seismic Zoning of Croatia

The territory of Croatia and neighboring regions is divided into 17 seismic source zones, considering available seismological and geological data. On this basis, seismic hazard elements (seismicity rate, maximum magnitude, b-value, probabilities of exceedance and return periods for a predefined set of magnitudes) are computed using the maximum likelihood method appropriate for treating data-sets with variable completeness thresholds. The values of long term expected peak horizontal acceleration obtained by using a combination of the deterministic and the probabilistic procedure are the highest in the Dubrovnik zone, while the Zagreb zone has the highest earthquake hazard in the continental part of the country.

A Contribution to Seismic Hazard Assessment in Croatia from Deterministic Modeling

Abstract—Some of the elements of regional seismic hazard in Croatia are assessed by computing synthetic accelerograms at a predetermined set of sites. The input dataset consists of structural models, parameters of seismic sources, and an updated earthquake catalog. Synthetic strong-motion time series for frequencies below 1 Hz are computed on a grid of sites using the modal summation technique. The long-period hazard is described by the distribution of estimated peak values of ground displacement, velocity and acceleration, while the short-period hazard is represented by the map of design ground acceleration values (DGA). The highest values of DGA exceeding 0.35 g on the base-rock level are found in the southeastern coastal part of the country, in the greater Dubrovnik area.

Attenuation of Peak Horizontal and Vertical Acceleration in the Dinarides Area

Peak acceleration attenuation relations for horizontal and vertical components are presented for the Dinarides region, based on 145 3-component accelerograms related to 46 earthquakes with local magnitudes of 4.5 or greater and with epicentral distances of less than 200 km as recorded on 39 recording sites in the greater Dinarides region. The attenuation functions were obtained by two-stage stratified regression on the local magnitude and epicentral distance as independent variables. The predicted peak acceleration values within the distance range covered by the data are comparable to the ones obtained for stiff-soil or rock sites when selected reference relations are used. The rather large average residuals are caused mostly by the lack of information on local site conditions and by the use of epicentral distance instead of fault distance.

Numerical Modeling of the Ston-Slano (Croatia) Aftershock Sequence

The rate of aftershock occurrence after the M6 Ston-Slano (Croatia) earthquake is modeled as the Epidemic Type Aftershock Sequence (ETAS). Increase of the modeled cumulative number of aftershocks with time was fitted to observations by the least-squares criterion using the combined grid-search and Monte-Carlo approach. This enabled not only the estimation of the most probable ETAS parameters, but also the determination of their confidence limits, as well as the estimation of the bias between them. It has been found that the bias is significant for some of the parameter pairs, regardless of the threshold magnitude assumed. Residual analyses revealed that all strong aftershocks (ML≥ 4.5) occurred during the periods of normal to high aftershock activity. There were two periods of quiescence in the sequence, both of which were followed by a strong aftershock.

BSHAP seismic source characterization models for the Western Balkan region

This manuscript presents the seismic source characterization models that were developed and used for the Western Balkan region in the framework of Harmonization of Seismic Hazard Maps in the Western Balkan Countries Project (BSHAP II) funded by NATO-Science for Peace and Security Program. Relevant knowledge about the geological and seismotectonic structure of Western Balkans and surrounding region was collected and utilized along with the BSHAP focal mechanism database and the BSHAP earthquake catalogue (Markušić et al. in Bull Earthq Eng 14(2):321–343, 2016. doi:10.1007/s10518-015-9833-z) to delineate seismic source models for different purposes. The super zone model of large zones bounds the regions with similar seismotectonic characteristics and catalogue completeness levels and was used for calculating the regional b-value of the magnitude recurrence relationship. Additionally, two models of smaller zones that represent the epistemic uncertainty in source geometry, maximum magnitude and style-of-faulting, were developed to be employed in the two-stage (circular and elliptical) smoothing procedure. Sets of sensitivity analyses are performed to support final estimates of some models’ parameters affecting the smoothed seismicity rate. The seismic source models and the logic-tree presented here are to be implemented in the probabilistic seismic hazard assessment for the seismic hazard maps of the Western Balkan region.

The 1667 Dubrovnik earthquake–some new insights

The year 2017 marks the 350th anniversary of the great 6 April 1667 Dubrovnik earthquake that caused extensive damage in a wide area around this old Dalmatian town (today in Croatia). This article presents the effects of the 1667 earthquake and examines the first few weeks following the catastrophe. Macroseismic data are reanalysed, for the first time available data are collected of the damage on the territory of Bosnia and Herzegovina (the territory which was in the 17th century under the Ottoman reign) and a new map of macroseismic intensities is presented. This map is in good agreement with the macroseismic field modelled using the SAF (Strong Attenuation at Fault Zones) model. We highlight some problems in the collection of macroseismic information, which are mainly a consequence of the complex political situation in the areas affected by the earthquake. The 1667 earthquake heavily impacted Dubrovnik and the Dalmatian coast. This event is thought to be the biggest one in the history of Dalmatia and practically defines seismic hazard in the coastal area of Croatia. For this reason, the main goals in this article are the improvement of the epicenter location and the determination of the moment magnitude.