eprintid: 2179 rev_number: 9 eprint_status: archive userid: 2 dir: disk0/00/00/21/79 datestamp: 2019-01-23 14:28:08 lastmod: 2019-01-23 14:28:08 status_changed: 2019-01-23 14:28:08 type: article metadata_visibility: show creators_name: Bossu, Remy creators_name: Grasso, Jean-Robert title: Stress analysis in the intraplate area of Gazli, Uzbekistan, from different sets of earthquake focal mechanisms subjects: MP1 subjects: MP6 subjects: RUZ subjects: SHC divisions: IP17 full_text_status: none abstract: Occurrence of intraplate earthquakes have been related either to reactivation of preexisting zones of weakness in a uniformly oriented regional stress field or to local stress changes. More recently, buildup of pore pressure anomalies has been proposed to explain both the low recurrence rate and some misorientation of rupture planes in the prevailing regional stress field. In this study, we analyze local stress field orientation in the area of the three Ms = 7.0 Gazli (western Uzbekistan) earthquakes by using different sets of earthquakes focal mechanisms. We show that stress tensor inversions from both seven 4.2 ≤ Ms ≤ 7.0, forty‐five 0.1 ≤ ML ≤ 3.2 and twenty‐five 1.0 ≤ ML ≤ 3.2 earthquake focal mechanisms give constant maximum horizontal stress direction in agreement with the one deduced from the India‐Asia collision. The best model for the local stress tensor exhibits a significant (25°) discrepancy from vertical for one of the principal stresses. We note, moreover, that the common assumption that one principal stress axis is oriented vertically is not strictly supported by stress states derived from earthquake focal mechanisms available in the world stress database. By evaluating each hypothesis of stress inversion methods from earthquake focal mechanisms, it is shown that, especially in intraplate settings, the first motion focal solution should be the most appropriate one for a formal inversion and that the magnitude of the considered event may not be the only criterion to assess the quality of a stress inversion. This is particularly timely because more and more focal mechanisms are moment tensor solutions instead of first motion solutions. Concerning the Gazli sequence, the slip conditions (pore pressure and frictional coefficient) are evaluated for each of the three mainshocks in terms of an independently determined local stress field. Because variations in orientations between local and regional stress field are not detected, and because the three mainshock fault planes seem to be relatively well oriented for a frictional activation in the local stress field, it is concluded that this seismic sequence is localized on preexisting weakness zones and is not due to local stress orientation anomalies. date: 1996 date_type: published publication: Journal of Geophysical Research volume: 101 number: B8 publisher: American Geophysical Union pagerange: 17645-17660 id_number: doi:10.1029/96JB01182 issn: 0148-0227 official_url: http://doi.org/10.1029/96JB01182 access_IS-EPOS: limited owner: Publisher citation: Bossu, Remy and Grasso, Jean-Robert (1996) Stress analysis in the intraplate area of Gazli, Uzbekistan, from different sets of earthquake focal mechanisms. Journal of Geophysical Research, 101 (B8). pp. 17645-17660. DOI: https://doi.org/10.1029/96JB01182