Seismic scattering and absorption mapping from intermediate-depth earthquakes reveals complex tectonic interactions acting in the Vrancea region and surroundings (Romania)

F. Borleanu, L. De Siena, C. Thomas, M. Popa, M. Radulian

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Abstract

The Vrancea region, located at the southeastern edge of the Carpathians arc bend, is a region of intense seismicity, whose major earthquakes produce hazard in southeastern Europe. Despite the consequent focus of the geophysical and geological community on providing accurate structural and dynamical models of Vrancea, these are still subject to numerous controversies and debates. In the present study, we use intermediate-depth seismicity recorded by the broadband stations of the Romanian Seismic Network between 2009 and 2011 to measure S-wave peak delay times and late-time coda quality factors. After mapping these two quantities in space, a cluster analysis provides a quantitative structural interpretation of the region in terms of different attenuation mechanisms affecting the seismic wave field, i.e. seismic scattering and seismic absorption. The results show that scattering is higher west and northwest of Vrancea, while absorption dominates in the Focsani Basin, located in the forearc region. In general, we obtain higher absorption in stable regions, with patterns emphasized at high-frequency affected by the presence of hydrocarbons and natural gas reservoirs in the upper crustal layers. Regions characterized by active seismicity and structural heterogeneity show higher scattering, spatially correlated with the highest velocity contrasts and the lowest density. The high-frequency scattering/absorption contrasts obtained using the cluster analysis depict a southwest-to-northeast lithospheric contrast, following the epicentral trend of Vrancea earthquakes, and characteristic of either lithospheric subduction or delamination. Low-frequency cluster analysis results, sampling deeper Earth layers, mark a unique high-absorption trend perpendicular to the epicentral trend, feasibly linked to Neogene volcanism, and induced by the back-arc mantle upwelling. Its most recent expression is Ciomadul volcano, located at the northwestern limit of the absorption trend.
Original languageEnglish
Pages (from-to)129-142
Number of pages14
JournalTectonophysics
Volume706-707
Early online date13 Apr 2017
DOIs
Publication statusPublished - 5 Jun 2017

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Romania
tectonics
earthquakes
scattering
earthquake
cluster analysis
trends
seismicity
interactions
arcs
coda
delamination
seismic waves
natural gas
upwelling water
wave field
seismic wave
volcanoes
hazards
S waves

Keywords

  • seismic attenuation
  • Vrancea region
  • intermediate depth earthquakes
  • peak delay times
  • coda quality factor
  • cluster analysis

Cite this

Seismic scattering and absorption mapping from intermediate-depth earthquakes reveals complex tectonic interactions acting in the Vrancea region and surroundings (Romania). / Borleanu, F.; De Siena, L.; Thomas, C.; Popa, M.; Radulian, M. .

In: Tectonophysics, Vol. 706-707, 05.06.2017, p. 129-142.

Research output: Contribution to journalArticle

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title = "Seismic scattering and absorption mapping from intermediate-depth earthquakes reveals complex tectonic interactions acting in the Vrancea region and surroundings (Romania)",
abstract = "The Vrancea region, located at the southeastern edge of the Carpathians arc bend, is a region of intense seismicity, whose major earthquakes produce hazard in southeastern Europe. Despite the consequent focus of the geophysical and geological community on providing accurate structural and dynamical models of Vrancea, these are still subject to numerous controversies and debates. In the present study, we use intermediate-depth seismicity recorded by the broadband stations of the Romanian Seismic Network between 2009 and 2011 to measure S-wave peak delay times and late-time coda quality factors. After mapping these two quantities in space, a cluster analysis provides a quantitative structural interpretation of the region in terms of different attenuation mechanisms affecting the seismic wave field, i.e. seismic scattering and seismic absorption. The results show that scattering is higher west and northwest of Vrancea, while absorption dominates in the Focsani Basin, located in the forearc region. In general, we obtain higher absorption in stable regions, with patterns emphasized at high-frequency affected by the presence of hydrocarbons and natural gas reservoirs in the upper crustal layers. Regions characterized by active seismicity and structural heterogeneity show higher scattering, spatially correlated with the highest velocity contrasts and the lowest density. The high-frequency scattering/absorption contrasts obtained using the cluster analysis depict a southwest-to-northeast lithospheric contrast, following the epicentral trend of Vrancea earthquakes, and characteristic of either lithospheric subduction or delamination. Low-frequency cluster analysis results, sampling deeper Earth layers, mark a unique high-absorption trend perpendicular to the epicentral trend, feasibly linked to Neogene volcanism, and induced by the back-arc mantle upwelling. Its most recent expression is Ciomadul volcano, located at the northwestern limit of the absorption trend.",
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note = "The present study was performed during a stay at the University of M{\"u}nster financed by a grant awarded by the German Academic Exchange Service (DAAD) in 2014. Data used in the present study were provided by the National Institute for Earth Physics (Romania) and processed within the National Data Centre in Magurele. Seismic Analysis Code (SAC) (Goldstein and Snoke, 2005) and GMT (Wessel et al., 2013) codes were used. We thank the College of Physical Sciences (University of Aberdeen) and the Santander Mobility Award for providing travel grant to LDS to complete this manuscript. We are grateful as well to the anonymous reviewer for his useful remarks which helped us to improve the paper.",
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T1 - Seismic scattering and absorption mapping from intermediate-depth earthquakes reveals complex tectonic interactions acting in the Vrancea region and surroundings (Romania)

AU - Borleanu, F.

AU - De Siena, L.

AU - Thomas, C.

AU - Popa, M.

AU - Radulian, M.

N1 - The present study was performed during a stay at the University of Münster financed by a grant awarded by the German Academic Exchange Service (DAAD) in 2014. Data used in the present study were provided by the National Institute for Earth Physics (Romania) and processed within the National Data Centre in Magurele. Seismic Analysis Code (SAC) (Goldstein and Snoke, 2005) and GMT (Wessel et al., 2013) codes were used. We thank the College of Physical Sciences (University of Aberdeen) and the Santander Mobility Award for providing travel grant to LDS to complete this manuscript. We are grateful as well to the anonymous reviewer for his useful remarks which helped us to improve the paper.

PY - 2017/6/5

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N2 - The Vrancea region, located at the southeastern edge of the Carpathians arc bend, is a region of intense seismicity, whose major earthquakes produce hazard in southeastern Europe. Despite the consequent focus of the geophysical and geological community on providing accurate structural and dynamical models of Vrancea, these are still subject to numerous controversies and debates. In the present study, we use intermediate-depth seismicity recorded by the broadband stations of the Romanian Seismic Network between 2009 and 2011 to measure S-wave peak delay times and late-time coda quality factors. After mapping these two quantities in space, a cluster analysis provides a quantitative structural interpretation of the region in terms of different attenuation mechanisms affecting the seismic wave field, i.e. seismic scattering and seismic absorption. The results show that scattering is higher west and northwest of Vrancea, while absorption dominates in the Focsani Basin, located in the forearc region. In general, we obtain higher absorption in stable regions, with patterns emphasized at high-frequency affected by the presence of hydrocarbons and natural gas reservoirs in the upper crustal layers. Regions characterized by active seismicity and structural heterogeneity show higher scattering, spatially correlated with the highest velocity contrasts and the lowest density. The high-frequency scattering/absorption contrasts obtained using the cluster analysis depict a southwest-to-northeast lithospheric contrast, following the epicentral trend of Vrancea earthquakes, and characteristic of either lithospheric subduction or delamination. Low-frequency cluster analysis results, sampling deeper Earth layers, mark a unique high-absorption trend perpendicular to the epicentral trend, feasibly linked to Neogene volcanism, and induced by the back-arc mantle upwelling. Its most recent expression is Ciomadul volcano, located at the northwestern limit of the absorption trend.

AB - The Vrancea region, located at the southeastern edge of the Carpathians arc bend, is a region of intense seismicity, whose major earthquakes produce hazard in southeastern Europe. Despite the consequent focus of the geophysical and geological community on providing accurate structural and dynamical models of Vrancea, these are still subject to numerous controversies and debates. In the present study, we use intermediate-depth seismicity recorded by the broadband stations of the Romanian Seismic Network between 2009 and 2011 to measure S-wave peak delay times and late-time coda quality factors. After mapping these two quantities in space, a cluster analysis provides a quantitative structural interpretation of the region in terms of different attenuation mechanisms affecting the seismic wave field, i.e. seismic scattering and seismic absorption. The results show that scattering is higher west and northwest of Vrancea, while absorption dominates in the Focsani Basin, located in the forearc region. In general, we obtain higher absorption in stable regions, with patterns emphasized at high-frequency affected by the presence of hydrocarbons and natural gas reservoirs in the upper crustal layers. Regions characterized by active seismicity and structural heterogeneity show higher scattering, spatially correlated with the highest velocity contrasts and the lowest density. The high-frequency scattering/absorption contrasts obtained using the cluster analysis depict a southwest-to-northeast lithospheric contrast, following the epicentral trend of Vrancea earthquakes, and characteristic of either lithospheric subduction or delamination. Low-frequency cluster analysis results, sampling deeper Earth layers, mark a unique high-absorption trend perpendicular to the epicentral trend, feasibly linked to Neogene volcanism, and induced by the back-arc mantle upwelling. Its most recent expression is Ciomadul volcano, located at the northwestern limit of the absorption trend.

KW - seismic attenuation

KW - Vrancea region

KW - intermediate depth earthquakes

KW - peak delay times

KW - coda quality factor

KW - cluster analysis

U2 - 10.1016/j.tecto.2017.04.013

DO - 10.1016/j.tecto.2017.04.013

M3 - Article

VL - 706-707

SP - 129

EP - 142

JO - Tectonophysics

JF - Tectonophysics

SN - 0040-1951

ER -