Incipient status of dyke intrusion in top crust – evidences from the Al-Ays 2009 earthquake swarm, Harrat Lunayyir, SW Saudi Arabia

Abstract

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 AlAys 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.

Structural Mapping of Dike-Induced Faulting in Harrat Lunayyir (Saudi Arabia) by Using High Resolution Drone Imagery

“…They used an analog dike that was arch-shaped and asymmetrical along the strike and thus closer to the surface, nearer to the dike's central part than its tips. The dike shape was inferred from the InSAR-modeled dike and the seismicity of the 2009 event, which are both shallower under the southern part of the graben than under the northern part (Mukhopadhyay et al, 2013;Xu et al, 2016;Abdelfattah et al, 2017). In the analog model, the fractures formed at the surface as a consequence of the dike opening; the fractures were closer to the dike where the dike was shallower but further away where the dike was FIGURE 9 | Rose diagrams showing orientations of (A) fractures in dike-parallel; (B) in oblique segments; (C) fractures extracted from InSAR data (Jónsson, 2012) in the north-western Harrat Lunayyir of the 2009 dike intrusion (see also Figures 1b,c); (D) eruptive fissures (or crater rows) belonging to the Harrat Lunayyir volcanic field and mapped by using BingMaps and Google Earth images (see also Figure 1b); (E) magnetic lineations in the whole Harrat Lunayyir volcanic field (Zahran, 2017;; (F) coastal tertiary regional dikes (mapped from USGS map 1963); (G) regional faults and undefined lineaments in the northern (from 23 • 00 to 28 • 00 N) Arabian Shield (Beziat and Bache, 1985;Figure 1a deeper.…”

Thermal mapping of the 2009 dyke emplacement at Harrat Lunayyir, Saudi Arabia

“…11). However, this was not indicative of an absence of seismic swarm in 2007, in October 2007, a volcanotectonic episode in the region commenced and was typified by an earthquake swarm (Al-Amri and Al-Mogren 2011; Mukhopadhyay et al 2013;Zobin et al 2013). Additionally, a swarm of more than 500 earthquakes began in October 2007 and ended in May 2008, indicating an origin with a NW-SE strike at a depth greater than 10 km.…”

“…After this peak, the volcanic activity was seen to gradually diminish. During the intrusion process, the dyke propagated to more shallow crustal levels, which may have contributed to a portion of the meter-scale fault slip on the western graben-bounding faults (Mukhopadhyay et al 2013;Pallister et al 2010). Zahran et al (2009), relying on a range of geodetic monitoring data, registered seismotectonic observations corroborating the dyke intrusion hypothesis.…”

“…The bulk of research on these earthquake swarms and their associated surface deformation indicated that the primary surface deformation might be partly associated with dyke propagation at a shallow depth and that the earthquake epicentres resided beneath the morphologically young volcanic crater cones (Pallister et al 2010). According to Mukhopadhyay et al (2013), the vertical dyke propagation initiated at crustal depths and exhibited a 5-day peak period (15-20 May 2009). After this peak, the volcanic activity was seen to gradually diminish.…”

Evolution of geothermal systems around the Red Sea

“…11). Recent seismic tomography investigation and analyses of focal mechanism of 2009 earthquake swarms indicate origin of the earthquakes at two depth bands (5-10 and 15-20 km) due to NW-SE trending magma intrusion around Harrat Lunayyir Mukhopadhyay et al 2012).…”