Crustal structure of the Dead Sea Basin from local earthquake tomography

Abstract

International audienceNew findings of the velocity structure of the crust across the Dead Sea Basin are obtained by applying tomography-based method to local earthquakes. We use P-wave traveltime of 614 earthquakes that occurred in the Dead Sea Basin in 1983-2009. At all depths, the Dead Sea Basin is characterized by lower velocities relative to both the eastern and western sides of the basin. There is significant seismic activity at a depth of about 20 km, mainly in the centre and the northern part of the basin. At shallow depths (<15 km) there is more seismic activity on the eastern side of the basin than on the western side, and the northern basin is generally more active than the southern basin. Asymmetry is also observed in the faults that border the Dead Sea Basin. The Arava Fault on the eastern side, with nearly vertical dip faulting, appears to be a clear boundary at all depths down to about 20 km. The depth extension of the Jericho Fault on the western side of the basin is definitely limited to less than 15 km. At greater depths of 20 km or more, the western side is only partially bounded by a fault. The concentration of earthquakes in the central part of the basin at depths larger than 15 km suggests that the Dead Sea Fault at those depths acts as one single fault that is located in, or near, the central axis of the basin. The existence of a number of clusters of earthquakes that spread from shallow depths of a few kilometres up to a depth of about 22 km, points to several defined faults that traverse the Dead Sea Basin. One such example is the aftershock sequence of the 2004 earthquake that occurred in the northern Dead Sea Basin. Seismic activity near Mt Sodom is relatively low and occurs at shallow depths down to 10 km, whereas at larger depths (≥15 km) it ceases. This implies that the whole structure is relatively shallow with no wide and deeper extension. Seismic activity near and within the Lisan Peninsula extends to somewhat larger depths (∼15 km), and then it ceases. The occurrence of earthquakes at large depths suggests that the upper and the lower crust are relatively cool, as was also suggested by earlier studies, pointing to the fact that the heat flow is significantly below the global average value

High-resolution local earthquake tomography of the southern Dead Sea area

“…These values are just assumed to be unrealistic (Mechie et al 2009). Furthermore, a significant decrease of seismic activity appears at 18 km depth—in our data set (Figs 3b and 8; Braeuer et al 2012) as well as in a long‐term observation of Hofstetter et al (2012).…”

“…The interaction of the fluids with the lower crust profoundly weakened the yield strength, causing the rapid subsidence within the past 1 Myr (ten Brink & Flores 2012, and references therein). The microseismic activity in the lower crust (Aldersons et al 2003; Hofstetter et al 2012; Braeuer et al 2012, Fig. 3b) is then explained by rapidly rising fluids, creating locally hydro‐fracturing even within the ductile crust (ten Brink & Flores 2012).…”

The association of micro‐earthquake clusters with mapped faults in the Dead Sea basin

“…The 640 relocated earthquakes show that the seismicity in the DSB has a maximum depth of ~25 km, as previously shown by Hofstetter et al . [], and a few kilometers less than the previous estimation of 32 km, by Aldersons et al . [], with peak activities at 12 and 17 km (Figure e).…”

Teleseismic traveltimes residuals across the Dead Sea basin

“…[], Hofstetter et al . [], and Braeuer et al . [] showed that the eastern side has equal or higher‐velocity values than the western side at all depths, from shallow depth down to about 20 km (see Figure ).…”

“…Based on the observed seismic activity at Mount Sodom, Hofstetter et al . [] reported that the entire structure is relatively shallow with no deep roots. The diapir is surrounded by the Amiaz plain and the southern Dead Sea basin on the western and eastern sides of Sodom salt diapir, respectively, are composed of light and slow sediments (see stratigraphic sections in Stein [], Bartov and Sagy [], Ben‐Avraham et al .…”