IASPEI - Picture Gallery

IUGG XXIV General Assembly July 2-13, 2007 Perugia, Italy
(S) - IASPEI - International Association of Seismology and Physics of the Earth's
Interior
JSS014 Oral Presentation 2265
Interaction of active fault and fold development: the Balanegra-Sierra de
Gador GPS network (Central Betic Cordillera, SE Spain)
Prof. Jesus Galindo-Zaldivar
Geodinamica Universidad de Granada
Antonio Gil, Carlos Marn-Lechado, Pedro Alfaro, Clara De Lacy, Francisco Jun
Garca-Tortosa, Angel Carlos Lpez-Garrido, Antonio Pedrera-Parias, Isabel Ramos,
Gracia Rodrguez-Caderot, Ana Ruiz-Constn, Carlos Sanz De Galdeano, Maria Jess
Borque
The Betic-Rif cordilleras have been formed in the western Mediterranean by the oblique convergence
related to the Eurasian-African plate boundary. The seismicity and the active tectonic structures are
distributed along a band of more than 300 km wide. In the Internal Zones of the Betic Cordilleras, the
development of large E-W oriented folds since the middle Miocene and related faults are the responsible
of the present-day relief. These active upper crustal structures formed in the hanging wall of major
detachments. The Balanegra-Sierra de Gdor region is located in the boundary of the central Betic
Cordillera and the Alboran Sea and shows a relatively more intense seismicity and tectonic activity than
the surrounding areas. The last seismic series occurred in December 1994- January 1995 with two
Mb=4.9 and Mb=5.0 mainshocks and more than 350 recorded events (Md>1.5). This shallow activity
occurred along the NW-SE oriented Balanegra normal fault, which determines the position of the coast
line along more than 10 km and extends to the Alboran Sea. The Balanegra Fault zone is formed by
several parallel faults with 1-10 m associated scarps producing a staircase morphology. The maximum
vertical slip is generally of several hundred of meters. The fault zone is located southwest of the Sierra
de Gdor antiform that determines the highest relieves of this region. Minor NW-SE oriented normal
faults indicate an ENE-WSW regional oriented extension. Seismic profiles points to the simultaneous
development in the region of large ENE-WSW folds and minor faults since the Miocene. A new nonpermanent
GPS network has been installed in order to study more in detail the present-day relationships
of large folds and faults development. For this purpose, in addition to measurement points installed in
the Balanegra fault zone, other points have been located in the Sierra de Gdor Antiform. A first
measurement campaign has been developed during the spring-2006 and GPS locations have been
determined with mm accuracy. In addition, two high precision leveling lines (accuracy of 0.2 mm) have
been established across the fault. Anyway, taking into account the expected low rates of tectonic
structures and the measurement precision, GPS network may provide accurate results after a period of
more than 5 years and high precision leveling after 2 years if there are not new seismic series in the
region. These data may help to quantify the tectonic model determined by NNW-SSE shortening
accommodated by fold development and relief uplift and orthogonal ENE-WSW extension responsible of
the normal fault activity.
Keywords: gps, faults folds, betics