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Geological Society, London, Special Publications; 2009; v. 316; p. 207-216;
DOI: 10.1144/SP316.13
© 2009 Geological Society of London

Articles

Speleoseismology and palaeoseismicity of Benis Cave (Murcia, SE Spain): coseismic effects of the 1999 Mula earthquake (mb 4.8)

R. Pérez-López1,*, M. A. Rodríguez-Pascua1, J. L. Giner-Robles2, J. J. Martínez-Díaz3, A. Marcos-Nuez4, P. G. Silva5, M. Bejar2 & J. P. Calvo1

1 Área de Riesgos Geológicos, Instituto Geológico y Minero de España, C/Ríos Rosas 23, Madrid 28003, Spain
2 Dpto. de CCAA y RRNN, Universidad CEU San Pablo, Madrid, Spain
3 Dpto. de Geodinámica, Facultad de Ciencias Geológicas, Universidad Complutense de Madrid, Spain
4 Grupo Especial de Rescate en Altura, GERA, Cuerpo de Bomberos de la Comunidad de Madrid, Spain
5 Dpto. de Geología, Universidad de Salamanca, Escuela Politécnica Superior de Ávila, Spain

* Corresponding author (e-mail: r.perez{at}igme.es)

This work describes the coseismic ceiling block collapse within Benis Cave (–213 m; Murcia, SE Spain), associated with the 1999 Mula earthquake (mb=4.8, MSK VII). The collapse occurred at –156 m into the Earthquake Hall, and as a consequence one small gallery became blind. We studied the geology, topography and active tectonic structures relevant to the cave. In addition, we carried out a seismotectonic analysis of the focal mechanism solutions, and also a fault population analysis on slickensides measured in fault planes in the cave. The stress and strain regime is interpreted as being congruent with the palaeoseismic evidence, and agrees with the fault kinematics established for cave galleries developed within fault planes and growth anomalies of coral flowstone. Our analysis suggests that one active segment (NNE–SSW) determined the morphology and topography of the Benis Cave, where strong to moderate palaeoearthquakes (6≤M≤7) took place. As a consequence of this intense seismic activity a small gallery collapsed. A new palaeoseismic structure, or seismothem, has been recognized, namely the effect of palaeoearthquakes affecting the pattern of development of the spatial coral flowstone distribution located at the bottom of the cave.