Paco

ISSN (print): 1698-6180. ISSN (online): 1886-7995 www.ucm.es/info/estratig/journal.htm Journal of Iberian Geology 38 (1) 2012: 113-126 http://dx.doi.org/10.5209/rev_JIGE.2012.v38.n1.39208

Recent tectonic model for the Upper Tagus Basin (central Spain)
Modelo tectónico reciente de la Cuenca Alta del Tajo (parte central española)

J.L. Giner-Robles*1, R. Pérez-López 2, P.G. Silva 3, A.Jiménez-Díaz 4, M.A. Rodríguez-Pascua 2
1

Dpto. Geología y Geoquímica. Facultad de Ciencias. Campus de Cantoblanco, Universidad Autónoma de Madrid. 28049- Madrid, Spain. jorge.giner@uam.es 2 IGME – Instituto Geológico y Minero de España. Área de Investigación y Peligrosidad en Riesgos Geológicos C/ Ríos Rosas 23, 28003 Madrid, Spain r.perez@igme.es, ma.rodriguez@igme.es 3 Dpto. Geología, EscuelaPolitécnica Superior de Ávila, Universidad de Salamanca. Avda. Hornos Caleros, 50. 05003-Ávila.España. Email: pgsilva@usal.es 4 Dpto. de Geodinámica. Facultad de Ciencias Geológicas. Universidad Complutense de Madrid. 28040 - Madrid. España (Spain). Email: ajimenezdiaz@geo.ucm.es

*Corresponding author

Received: 08/12/2011 / Accepted: 08/03/2012

Abstract $FWLYH WHFWRQLFV ZLWKLQ WKH 8SSHU 7DJXV%DVLQ LV UHODWHG WR WKH OLWKRVSKHULF ÀH[XUH DIIHFWLQJ WKH 3DODHR]RLF EDVHPHQW RI WKH EDVLQ 7KLV ÀH[XUH GLVSOD\V 1(6: WUHQGLQJ %HVLGHV WKLV VWUXFWXUH LV LQ DJUHHPHQW ZLWK WKH UHJLRQDO DFWLYH VWUHVV ¿HOG GH¿QHG E\ WKH maximum horizontal stress with NW-SE trending. In this tectonic framework, irregular clusters of instrumental seismicity (Mw< 5.0) fade in the zone bounded by the Tagus River andthe Jarama River valleys. These clusters are related to major NW-SE trending faults of suspected strike-slip kinematics. Moreover, reverse faults with NE-SW trending are affected by the strike-slip system as well. Despite the reverse faults are in agreement with the present SHMAX orientation, though, they apparently are blocked as seismogenic sources (scarce instrumental seismicity recordedtoday). In addition, we have determined the regional and local stress/ VWUDLQ ¿HOGV DQG WZR GLIIHUHQW IUDFWXUH SDWWHUQV ZHUH REVHUYHG +HQFH ZH KDYH GLYLGHG WKH DUHD LQ WZR ]RQHV  WKH ODWHUDO EDQGV RI WKH EDVLQ GH¿QHG E\ UHYHUVH IDXOWLQJ 1(6: WUHQGLQJ DQG VWULNHVOLS IDXOWLQJ 1:6( WUHQGLQJ DQG  WKH FHQWUDO ]RQH RI WKH basin characterized by shallow normal faulting and NE-SW trendingstrike-slip faults. Furthermore, surface faulting and liquefacWLRQ VWUXFWXUHV DUH GHVFULEHG DIIHFWLQJ 0LGGOH WR /DWH 3OHLVWRFHQH ÀXYLDO GHSRVLWV VXJJHVWLQJ LQWUDEDVLQDO SDODHRVHLVPLF DFWLYLW\  < M < 6.5) during the Late Quaternary. The obtained structural and tectonic information has been used to classify and characterize the Upper Tagus Basin as a semi-stable intraplate seismogenic zone, featuredby Pleistocene slip-rates < 0.02 mm/yr. This value is low but it affords the occurrence of Pleistocene paleoearthquakes. Keywords: Seismotectonics, Focal mechanisms, Paleoseismicity, Pleistocene, Upper Tagus Basin

114

Giner-Robles et al. / Journal of Iberian Geology 38 (1) 2012: 113-126

Resumen /D WHFWyQLFD DFWLYD GH OD &XHQFD $OWD GHO UtR 7DMR HVWi FDUDFWHUL]DGD SRU OD SUHVHQFLD GH XQDÀH[LyQ OLWRVIpULFD ORFDOL]DGD HQ HO EDVDPHQWR SDOHR]RLFR \ FX\R HMH VH RULHQWD VHJ~Q 1(6: (VWD ÀH[LyQ HV FRKHUHQWH FRQ HO HVWDGR GH HVIXHU]RV DFWXDO HQ OD ]RQD GH¿QLGR PHGLDQWH OD RULHQWDFLyQ GHO HVIXHU]R Pi[LPR KRUL]RQWDO 6+0$; VHJ~Q 1:6( (Q HVWH FRQWH[WR OD VLVPLFLGDG HQ HO borde sur del Sistema Central aparece concentrada en fallas direccionales según NW-SE, registrándose terremotosde magnitud < 5.0 (S. XX). Estos desgarres sectorizan el sistema de fallas inversas (NE-SW) que estructuran la cadena montañosa, las cuales a pesar de estar orientados coherentemente con el estado actual de esfuerzos, aparecen bloqueados o desactivados como fuentes VLVPRJpQLFDV /D JHRPHWUtD GH OD ÀH[XUD FRQGLFLRQD OD RFXUUHQFLD GH XQD ]RQD GH FRQFHQWUDFLyQ DQyPDOD GH HVIXHU]RV TXH UHVXOWD en la...