UNIVERSITY OF BUCHAREST
FACULTY OF PHYSICS

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Conference: Bucharest University Faculty of Physics 2019 Meeting


Section: Atmosphere and Earth Science; Environment Protection


Title:
Mapping the fundamental frequency on the Moesian Platform using single station analysis


Authors:
Alina COMAN(1,2), Elena-Florinela MANEA(2), Carmen Ortanza CIOFLAN(2), Mircea RADULIAN(2)


*
Affiliation:
1)University of Bucharest, Faculty of Physics, 077125, Magurele, Romania

2)National Institute for Earth Physics, PO BOX MG2, 077125, Magurele, Romania


E-mail
coman@infp.ro


Keywords:
Moesian Platform, ambient vibration, fundamental frequency of resonance of the S-wave


Abstract:
The strong effects at long periods observed in the extra-Carpathian area of Romania during large Vrancea intermediate-depth earthquakes are explained by the influence of both source mechanism and geological structure properties. A complex basin geometry and the low seismic velocities of the sediments are the primary responsible for the large amplification and long duration of the seismic records from the extra-Carpathian area during intermediate-depth earthquakes. In this study, we identify and map the fundamental frequency of resonance on the Moesian platform through the computation of H/V spectral ratios from three-component single station measurements of ambient vibration. We consider 130 seismic stations of the seismic network belonging to the National Institute of Earth Physics (Neagoe et al., 2016) and the ones deployed during two international projects: Carpathian Arc Lithosphere X-Tomography – CALIXTO (1999, see Martin et al., 2005) and South Carpathian Project - SCP (2009-2011, see Ren et al., 2013). The fundamental frequency of resonance is higher along the Carpathians orogeny delimiting the Moesian Platform to the North (values between 2 and 13 Hz). By contrast, inside the Carpathian foreland, it varies from very low values (minimum 0.074 Hz or 13 s) in Focsani basin up to 0.35 Hz. Outside of the Carpathian foreland, the predominant peak is observed from 0.13 Hz and up to high values (15 Hz) corresponding nearly to rock conditions. This pattern of resonance frequency leaves its mark on the frequency content of the seismic ground motion recorded in the extra-Carpathians area, including the long-period propagating waves observed during Vrancea earthquakes.


References:

Martin, M. J. R. R., & Ritter, J. R. R. (2005). High-resolution teleseismic body-wave tomography beneath SE Romania—I. Implications for three-dimensional versus one-dimensional crustal correction strategies with a new crustal velocity model. Geophysical Journal International, 162(2), 448-460.

Neagoe C., Grecu B., Manea L. M., (2016). Earthquake monitoring at different scales in Romania, Proceedings 16th International Multidisciplinary Scientific GeoConference SGEM 2016, Albena, Bulgaria, Book 1, Vol. 3, 459 - 466.

Ren, Yong, et al. (2013). Crustal structure of the Carpathian–Pannonian region from ambient noise tomography. Geophysical Journal International 195.2 : 1351-1369.



Acknowledgement:
This paper contains data sets deployed during two temporary networks: South Carpathian Project – SCP (2009 – 2011) and Carpathian Arc Lithosphere X-Tomography – CALIXTO (1999). This study was made in the framework of the project PN 19080102.