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Non-Volcanic Earthquake Swarm Near the Harrat Lunayyir Volcanic Field, Saudi Arabia
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  • Mohammad Youssof,
  • P. Martin Mai,
  • Adriano Nobile,
  • Sigurjón Jónsson
Mohammad Youssof
King Abdullah University of Science and Technology (KAUST)

Corresponding Author:[email protected]

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P. Martin Mai
King Abdullah University of Science and Technology (KAUST)
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Adriano Nobile
King Abdullah University of Science and Technology (KAUST)
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Sigurjón Jónsson
King Abdullah University of Science and Technology (KAUST)
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Abstract

Understanding the origin of seismic swarms can be controversial, especially when they occur near volcanic areas. Here, we investigate a seismic sequence which is steadily active in a non-volcanic area close by the volcanic field of Harrat Lunayyir in the western shield of Arabia. Our results unveil a planar zone of seismicity with ~5 km long E-W, sub-vertically ~9 km south-dipping structure, which is characterized by a dominant tensional focal mechanism. Independent evidence for the tectonic style dominance came from assessing the ground deformation images using the InSAR technique. This local seismicity might be attributed to a reactivated structure along a regional weakness zone of the Najd Fault System, which dominates the Precambrian structure of our area. Comparing the effects of high- and low-frequency datasets for the moment tensor inversion conclude a consistency of our solution. The frequency index analysis for P- and S- waves spectral datasets, does not suggest fluid-driven processes. We observe average stress drop of ~5.40 MPa with corner frequency of ~2.75 Hz. Our study confirms a localized reactivation of a brittle crustal seismogenic zone in the area of interest. This interpretation relies on the integration of several analysis methods, including spatial and magnitude-frequency distributions statistics.