Incipient status of dyke intrusion in top crust – evidences from the Al-Ays 2009 earthquake swarm, Harrat Lunayyir, SW Saudi Arabia
Dasgupta, Basab Mukhopadhyay , Saad Mogren , Manoj Mukhopadhyay & Sujit . 2013
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 (5–10 and 15–20 km) in upper crust without
volcanic eruption. We investigate an anatomy of the dyke-intrusion model that
supports the mechanism for the swarm itself with seismotectonics, pore pressure
diffusion process and inference model. Inferred dyke-intrusion initially started at
depth had a five-day peak period (15–20 May 2009) since inception of eventrecordings,
following which the activity diminished. The process of pore pressure
perturbation and resultant ‘‘r–t plot’’ with modelled diffusivity (D ¼ 0.01) relates
the diffusion of pore pressure to seismic sequence in a fractured poro-elastic fluidsaturated
medium. The spatio-temporal b-values show high b-values (41.3)
along the zone of dyke intrusion (length 10 km and height 5 km) at *20km
depth. The main-shock and other prominent earthquakes originated on a
moderate b-value zone (*1.0). Temporal b-value analysis indicates an
exceptionally low b-value (*0.4) during the main-shock occurrence. The Al-
Ays lava-field is inferred to underlie a seismic volume trending NW-SE bounded
on both sides by two NW-SE trending fault systems, dipping 40–508 opposite to
each other within a proposed nascent rift setting.
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 (…