Seismic activity along fault branches of the Dead Sea Jordan transform system: The Carmel-Tirtza fault system

About 550 earthquakes (1.0 less than or equal to M(L) less than or equal to 5.3) along the Carmel-Tirtza fault, a branching fault of the Jordan-Dead Sea Transform System, recorded by the Israel Seismograph Network (ISN) between 1984 and 1994 were analyzed. The seismicity pattern reveals significant activity often confined to known surface traces of active faults or within local grabens. Earthquake-clusters are also observed. The seismicity pattern within the Mediterranean seems more diffuse, possibly due to observational inaccuracies and insufficient knowledge of how the Carmel-Tirtza fault system extends towards the northwest. The seismicity along the Carmel-Tirtza fault system since the beginning of this century is characterized by a b value of about 0.9. For 15 events with 3.1 less than or equal to M(L) less than or equal to 5.3 we found seismic moment estimates, M(0), of 0.7 X 10(14)less than or equal to M(0) less than or equal to 10(17) Nm and Brune stress drop estimates, Delta sigma, between 0.9 and 16.4 MPa. These characteristics are comparable to those for events occurring on the main Dead Sea-Jordan Transform fault. Ten individual earthquake focal mechanisms and three joint focal mechanisms for earthquake clusters have been obtained. Towards the northeastern part of the Carmel-Tirtza fault system a left-lateral motion seems to dominate, while the seismicity pattern and the focal mechanism solutions near the branching of the Carmel-Tirtza fault and the Dead Sea-Jordan Rift suggest the present-day existence of a complicated tectonic regime. Stress inversion assuming one stress tensor for the whole region indicates NNE-SSW extension and WNW-ESE compression.