Subsurface imaging of the Harrat Lunayyir 2007–2009 earthquake swarm zone, western Saudi Arabia, using potential field methods
, Hakim Saibi, Saad Mogren, Manoj Mukhopadhyay, Elkhedr Ibrahim . 2018
The Harrat Lunayyir (HL) 2007–2009 earthquake swarm has attracted much scientific interest mainly due to its occurrence within the Large Igneous Province (LIP) of Saudi Arabia. Qualitative interpretation of aeromagnetic anomalies is suggestive of linear dike-like anomalies, striking NW-SE, across the earthquake swarm zone (ESZ). Residual Bouguer anomaly data for HL range between −4.3 and 1.5 mgal and show a 20km-wide gravity low flanked by lateral gravity highs. The axial-zone of low gravity corresponds tothe ESZ cluster. Employing a threedimensional (3D) inversion of the residual gravity field with a one-dimensional (1D) P-wave velocity model as a proxy for background density variations with depth, we imaged a mid-to-upper crustal low density zone (>10km depth). We interpret this zone as the source area of ascending magma that intruded into the upper crust underlying the HL during the 2009 seismic crisis. The inversion also highlights lower than average density rocksbeneaththewestern partsofthe HLwhereasits easternpart iscomposedofrocksofhigherdensity. The3D magnetic inversions lead us to infer magmatic intrusion of lower magnetic susceptibility at this locality extending vertically from 1.57km altitude (above sea level) to its bottom edge at 10.8km depth (below sea level). Based on theseresults, the 2007–2009 ESZ islikely associated withrift-relatedextension associated withthe Red Sea spreading, where a trans-crustal magmatic plumbing system extends to depths of about 10km beneath the centre of HL.
The 2009 earthquake-swarm in the Al-Ays volcanic zone in Harrat-Lunayyir in
NW Saudi-Arabia is unique because of its intense character and focal-depth
distribution at two depth bands (…