Tectonic regimes and stress patterns in the Vrancea Seismic Zone: Insights into intermediate-depth earthquake nests in locked collisional settings

Laura Petrescu, Felix Borleanu, Mircea Radulian, Alik Ismail-Zadeh, Liviu Matenco

Research output: Contribution to journalArticleAcademicpeer-review

Abstract

Earthquake nests are anomalous clusters of seismicity located far from active collisional systems in intraplate, locked suture zones, or the deep part of relic subducted slabs, challenging classic earthquake generation mechanism theories. The Vrancea Seismic Zone in Romania is such an upper-mantle seismic nest located in the SE Carpathians, releasing the largest strain in continental Europe. To better understand earthquake generation and the relationship with lithospheric deformation, we estimate earthquake source parameters in Vrancea and surrounding regions between 2014 and 2020, and determine the stress field via focal mechanism inversion and unsupervised machine learning. In the crustal domain, maximum horizontal stress is in agreement with surface fault kinematics and GPS-derived S-SE trending horizontal plate velocities relative to Eurasia, implying that tectonic stress is vertically coherent on a crustal scale. The stress regime changes from transpression beneath the orogen to transtension towards the foreland where movement is accommodated along major crustal faults, and tension further away from the epicentre, in the Moesian Platform and the North Dobrogea Orogen. Inside the seismogenic body vertical tension and an overall compressive regime dominates, implying that vertical elongation may be the driving mechanism for brittle failure and that stress is transmitted along the sinking slab to the surface. However, the retrieved stress ratios are low: ~0.2 for mantle earthquakes Mw>4 and ~0.4 for Mw
Original languageEnglish
Article number228688
Pages (from-to)1-17
Number of pages17
JournalTectonophysics
Volume799
DOIs
Publication statusPublished - 20 Jan 2021

Bibliographical note

Funding Information:
LP is supported by the Romanian Ministry of Research and Innovation Research Grant NUCLEU?CIRRUS PN18150101/2018. Data for this analysis are freely available through the National Institute for Earth Physics upon request (www.infp.ro). We are grateful to Prof. Randell Stephenson, Piero Poli and an anonymous reviewer for critical and valuable comments that improved the manuscript. Most figures were made using GMT software (Wessel and Smith, 1998).

Funding Information:
LP is supported by the Romanian Ministry of Research and Innovation Research Grant NUCLEU–CIRRUS PN18150101/2018 . Data for this analysis are freely available through the National Institute for Earth Physics upon request ( www.infp.ro ). We are grateful to Prof. Randell Stephenson, Piero Poli and an anonymous reviewer for critical and valuable comments that improved the manuscript. Most figures were made using GMT software ( Wessel and Smith, 1998 ).

Publisher Copyright:
© 2020 Elsevier B.V.

Keywords

  • Crust-mantle coupling
  • Focal mechanisms
  • Seismic nest
  • Stress inversion

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