Archaeoseismology and Palaeoseismology in the Alpine ... - Tierra

1 st INQUA‐IGCP‐567 International Workshop on Earthquake Archaeology and Palaeoseismology
DATING PALEO‐SEISMIC ACTIVITY ON THE CARMEL FAULT
DURING THE QUATERNARY, MT. CARMEL, ISRAEL
Braun, Y. (1, 2), Bar‐Matthews, M. (2), Ayalon, A. (2), Kagan, E.(1,2) and Agnon, A. (1)
(1) Institute of Earth Sciences, The Hebrew University of Jerusalem, 91904, ISRAEL. yael.braun@mail.huji.ac.il
(2) Geological Survey of Israel, 30 Malkhe Israel St., Jerusalem 95501, ISRAEL.
Abstract: Mt. Carmel in northern Israel, a continental uplift ca. 500 m above sea level, is defined by a NW‐NNW fault, a branch of the Dead Sea
Transform System (DST). The Carmel fault (CF) is observed as a wide zone of deformation about which very little is known concerning the
extent of seismic activity during the Quaternary. During the past 3 decades some 47 earthquakes (M>2) occurred along this fault zone with the
strongest recorded in 1984 (M = 5.3). Using accurate 230Th/234U ages of collapsed speleothems, we reconstructed seismic activity in Denya
Cave, Haifa. During the last 80 ka, 5 age clusters are recognized, separated by periods of quiescence (of an order of 10 millennia). The last
cluster appears ca. 11 ka, whilst indications for some younger activity remain to be confirmed.
Key words: earthquakes, paleoseismology, speleothem, seismite
INTRODUCTION
Mt. Carmel in the north of Israel, a manifestation of
tectonic movements, is a continental uplift of more than
500m above sea level. This uplift is defined by the NW to
NNW Carmel Fault (CF), a branch of the left‐lateral Dead
Sea Transform (DST). The DST lies between Arabia and the
Sinai‐Levant Block (Fig. 1) and exhibits a slip rate of
5.0±1.5 mm/yr (LeBeon et al., 2008). The CF, which
continues into the Mediterranean continental shelf
(Hofstetter et al., 1989), is observed as a wide zone of
deformation rather than a single fault trace (Rotstein et
al., 1993).
The CF along with the Gilboa Fault (GF), combine to
create a seismically active zone stretching for
approximately 130km (Hofstetter et al., 1996; Fig. 2). On
August 24, 1984 an earthquake along the CF (of a
magnitude {ML} of 5.3) caused slight damage in Haifa and
nearby towns (all seismic data derived from the
Geophysical Institute of Israel:
http://www.seis.mni.gov.il/html/seis/seis_search.html).
This earthquake aroused much interest since very little
was known concerning the extent of seismic activity
around Mt. Carmel. This seismic event further
emphasized the need to understand the tectonic regime
of a densely populated and industrialized area. Scholars
(Hofstetter et al.1996) also presented data on a series of
ca. 550 earthquakes (1.0 ≤ M L≤ 5.3) monitored along the
CF during the decade between 1984 and 1994.
Attempts to understand the tectonic regime of a
seismically active area necessitate paleoseismic research.
Karstic caves can preserve paleoseismic evidence, which
can provide fundamental elements for seismotectonic
knowledge, seismogenic descriptions and consequently,
the evaluation of seismic hazards in an area.
Broken or deformed cave deposits (speleo‐seismites) can
be used for paleoseismic research since they can be dated
with radiometric techniques (e.g. Davenport, 1998;
Lacave et al., 2004; Kagan et al.,
16
2005). Thus, they contribute to an earthquake data base
as an independent source of information on major
earthquake recurrences (Kagan et al., 2005).
The U‐Th method, which has a 350 to 500 ka limit, can
vastly increase the length of the seismic record during the
Quaternary by enabling us to date the time between a
break on a speleothem and its regrowth.
Fig. 1: A regional map showing the setting of DST separating
ARABIA from Sinai‐Levant Block.
Scholars (e.g. Becker et al., 2005; 2006; Kagan et al., 2005)
have proposed that a fundamental aspect of a concise
earthquake catalogue is based on a multi‐archival
approach, which not only enables confirmation of each of
the separate findings, but allows for better understanding
of the spatial influence of earthquakes on different
geological environments and their connections to tectonic
settings of a region. Paleoseismic research in Israel,