Cave Deposits as Recorders of Paleoseismicity: a Record from Two Caves Located 60 km West of the Dead Sea Transform (Jerusalem, Israel)
by
Elisa J. Kagan
The Hebrew University of Jerusalem and The Geological Survey of Israel
Coauthors: Amotz Agnon (The Hebrew University of Jerusalem), Miryam Bar-Matthews (The Geological Survey of Israel), Avner Ayalon (The Geological Survey of Israel)

Research of past earthquakes, typically retrieving records from soft sediment deformations, can benefit from the study of rockfalls and deposits in caves. Dating of damaged speleothems and deposits overgrowing rockfalls constrain the dates of earthquakes. The caves, located 60 km west of the Dead Sea Transform, record earthquake damage from Dead Sea Transform earthquakes and, possibly, smaller local intraplate events. We have compiled a paleoseismic record from two caves near Jerusalem, Israel. We investigated and refuted non-seismic sources of collapse. Dominant EW and NS orientation of collapsed speleothems were measured and are equivalent to Dead Sea Transform earthquake motion directions. Damage such as severed stalagmites, collapsed pillars, ceiling blocks, and various stalactites were surveyed. We identified "new generations" of speleothem growth on collapses. This post-collapse precipitation constrains ages of collapse. Laminae above and below the unconformity were separated and dated by the 230Th/234U method. We compared the carbon and oxygen isotopic record of the laminae adjacent to the tectonic unconformities with the well-dated isotopic record of Soreq Cave speleothems, as was reconstructed for the last 185 Ky for paleoclimate purposes (Bar-Matthews et al., 2000; Ayalon et al., 2002). This comparison vastly improves the ages. Thirty-nine collapses were sampled, of which at least eighteen separate events were dated. Of the Holocene events, all correlate with archeologically and geologically recorded earthquakes. Of the five events between 70-20 ky, four correlate with lacustrine seismites in the Lisan Formation (paleo-Dead Sea), while the fifth event occurred during a hiatus in that lacustrine sequence. Events older than 70 ky are, at present, the only paleoseismic record of its age studied in the region. The long Late Pleistocene record is useful for correlation with independent lacustrine records and for substantiation of the method, while the Holocene events are valuable for seismic hazard assessment.

Correspondence: elisak@pob.huji.ac.il

Date received: February 28, 2002