Imaging of magma intrusions beneath Harrat Al-Madinah in Saudi Arabia

• Precise local and teleseismic data are used to obtain fine tomography beneath Harrat Al-Madinah, Saudi Arabia.
• Strong heterogeneity and magma reservoir are revealed under the study area.
• A magma reservoir exists beneath a terrain dominated by trachytic domes and tuff rings with a seismic swarm.
• Magmatism along the western margin of Arabia is related to uplifting and thinning of its lithosphere due to the Red Sea rifting.

High-resolution tomographic images of the crust and upper mantle beneath Harrat Al-Madinah, Saudi Arabia, are obtained by inverting high-quality arrival-time data of local earthquakes and teleseismic events recorded by newly installed borehole seismic stations to investigate the AD 1256 volcanic eruption and the 1999 seismic swarm in the study region. Our tomographic images show the existence of strong heterogeneities marked with low-velocity zones extending beneath the AD 1256 volcanic center and the 1999 seismic swarm area. The low-velocity zone coinciding with the hypocenters of the 1999 seismic swarm suggests the presence of a shallow magma reservoir that is apparently originated from a deeper source (60–100 km depths) and is possibly connected with another reservoir located further north underneath the NNW-aligned scoria cones of the AD 1256 eruption. We suggest that the 1999 seismic swarm may represent an aborted volcanic eruption and that the magmatism along the western margin of Arabia is largely attributed to the uplifting and thinning of its lithosphere by the Red Sea rifting.