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FACULTY OF PHYSICS

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2025-08-21 0:50

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Conference: Bucharest University Faculty of Physics 2025 Meeting

Section: Atmosphere and Earth Science; Environment Protection

Title:

integrated seismic zone characterization and velocity modeling for accurate earthquake relocation in Romania

Authors:

Marius MIHAI(1,2), Mircea RADULIAN(1,2,3,4), Andreea CRAIU(1), Marius Craiu(1), Raluca DINESCU(1), Alexandru MARMUREANU(1)

^*
Affiliation:

1)National Institute for Earth Physics, Romania

2)University of Bucharest, Faculty of Physics, Magurele, Romania

3)Romanian Academy, Bucharest, Romania

4)Academy of Romanian Scientists, Bucharest, Romania

E-mail

nicu.mihai@infp.ro

Keywords:

earthquake catalogue, velocity model

Abstract:

This study aims to develop minimum 1-D velocity models for two seismically active regions in Romania (Banat-Crișana, Danubian) Vest Area, and Vrancea—using the Joint Hypocenter Determination (JHD) technique implemented through the VELEST code. The models incorporate station delays to correct for local site effects and instrument-specific biases, significantly improving the accuracy of earthquake hypocenter locations. The Banat-Crișana zone (western Romania), Danubian zone (south-western Southern Carpathians), and Vrancea zone (Eastern Carpathians) are geologically distinct regions that have experienced recent seismic activity, providing a high-quality dataset for analysis. For the purpose of testing the feasibility of developing a velocity model over a broader region, the Banat-Crișana and Danubian zones are treated as a single extended area caled Vest Area. Input events were selected based on quality criteria: a minimum of 7 P and S wave phases for Banat-Crișana and 11 for the Danubian and Vrancea zones, RMS residuals below 1.0 s, and azimuthal GAP values under 180°. Multiple input models were tested for each region to identify the optimal minimum 1-D velocity model through iterative JHD inversion. By incorporating station corrections and accounting for lateral velocity variations, the resulting models lead to improved hypocentral determinations and clearer seismicity patterns. The refined earthquake locations enhance the resolution of seismic clusters and support the creation of a more accurate and homogeneous earthquake catalogue. This approach also provides a framework for future seismic hazard assessment and tectonic analysis across Romanian seismic zones.

References:

Armeanu, Iulia; Chircea, Andreea; Ciobanu, Iulia; Craiu, Andreea; Craiu, George Marius; Dinescu, Raluca; Mihai, Marius; Predoiu, Andreea ; Tolea, Andreea; Varzaru, Lavinia-Cristina; Borleanu, Felix; Neagoe, Cristian; Radulian, Mircea; Mihaela, Popa (2023), “Database of the 2023 seismic sequence recorded in Gorj area (Romania)”, Mendeley Data, V1, doi: 10.17632/ds4hwchk

Kissling, E., Ellsworth, W. L., Eberhart-Phillips, D., & Kradolfer, U. (1994). Initial reference models in local earthquake tomography. Journal of Geophysical Research: Solid Earth, 99(B9), 19635-19646.

Kissling, E., Schmid, S. M., & Ansorge, J. (1995). A new method to determine the P-wave velocity structure of the crust and the uppermost mantle from refracted seismic waves. Geophysical Journal International, 121(3), 803-815.

Popa, Mihaela; Chircea, Andreea ; Dinescu, Raluca; Neagoe, Cristian ; Grecu, Bogdan; Borleanu, Felix (2022), “Romanian Earthquake Catalogue (ROMPLUS)”, Mendeley Data, V2, doi: 10.17632/tdfb4fgghy.2

Raileanu V. and CEEX project members. 2008. Map of the main fault systems in Romania. CEEX Project no. 647/2005

Zaharia, B., et al. (2017). "Crustal Structure in the Western Part of Romania from Local Seismic Tomography." IOP Conference Series: Earth and Environmental Science 95: 032019.

Acknowledgement:

This study was carried out within the National Research Program (projectSOL4RISCnoPN23360101) and Marius Nicu Mihai’s PhD grant. The seismic network mentioned is the Romanian Seismic Network (https://doi.org/10.1007/978-3-319-14328-6_9) belonging to the National Institute for Earth Physics (NIEP). Seismic information–ROMPLUS earthquake Catalogue (http://www.infp.ro/index.php?i=romplus).