Journal of Asian Earth Sciences 241 (2023) 105484 Available online 12 November 2022 1367-9120/© 2022 Elsevier Ltd. All rights reserved. Insights into the relationship between the Red Sea rift-related structures and the seismo-volcanic activity in Harrat Lunayyir, Saudi Arabia: A seismic tomography study Mohamed F. Abdelwahed a, * , Faisal A. Alqahtani a , Nabil N. El-Masry a , Sherif M. El-Hady b a Geohazards Research Center, King Abdulaziz University, Jeddah, Saudi Arabia b National Research Institute of Astronomy and Geophysics, Cairo, Egypt A R T I C L E INFO Keywords: Seismic tomography Magma intrusions Harrat Lunayyir Mabahiss Deep Zabargad Shear Zone Red Sea Saudi Arabia ABSTRACT Harrat Lunayyir is one of the youngest Cenozoic volcanic felds in western Saudi Arabia, which in 2009 expe- rienced a seismic swarm of about 34,000 events with a maximum magnitude of M5.4. Many studies debated about the relationship of a depicted shallow-level magma intrusion with the Red Sea rifting and the channelized northward fow from the Afar mantle plume. In this study, a detailed seismic tomography inversion for the P- and S-wave velocities, and the Poisson’s ratio structures beneath Harrat Lunayyir and the adjacent Red Sea offshore area is presented. The tomographic images showed evidence of magma intrusions beneath the Lunayyir Swarm Area (LSA) characterized by low P- and S-wave velocity and high Poisson’s ratio anomalies down to 21 km depth. These anomalies are in juxtaposition with some high-velocity anomalies attributed to remnants of solidifed magma intrusions relevant to previous episodes of volcanicity. Beneath the Red Sea, the lithospheric mantle structure is clearly observed as a high P-wave velocity high-Poisson’s ratio anomaly at a depth of 20–40 km. Traces of high-Vp anomalies with anomalous Poisson’s ratio are observed in the area between the Red Sea and the LSA suggesting that a channel of hot lithospheric mantle material may link the Red Sea rift structure with the LSA. We suggest that the Red Sea drifting and its related processes in the Zabargad Shear Zone might have signifcantly contributed to the early formation of the Lunayyir volcanic feld and could possibly have in an impact on any magmatic activity in the future. 1. Introduction The western coast of Saudi Arabia is characterized by Cenozoic basaltic felds, known as the harrat, distributed parallel to the NW-SE and the N-S trends of the Red Sea and the Makkah-Madinah-Nafud (MMN) volcanic line, respectively. Throughout the history, several volcanic eruptions are observed in the harrat. The last and most signif- icant volcanic eruption, commonly referred to as the “historical erup- tion” occurred in CE 1256 in Harrat Rahat near the holy city of Al- Madinah where six cinder cones and a 23 km-long lava fow were formed along a 2.25 km long fssure (Camp et al., 1987). This eruption lasted for 52 days and was preceded by fve days of seismic activity culminated with an M4.4 magnitude earthquake just before the eruption of the volcano (El-Masry et al., 2013; Abdelwahed et al., 2020). Recently, in May 1999, an earthquake swarm presumably caused by an aborted volcanic eruption occurred 20 km to the south of the historical eruption at a 10–15 km depth (Abdelwahed et al., 2016) and exhibited a moderate seismic swarm (M < 3.3) of ~ 500 events. In May 2009, a seismic swarm of more than 34,000 events occurred in Harrat Lunayyir with the largest magnitude M = 5.4 and the seismic moment = 5.3x10 17 Nm (Baer and Hamiel, 2010). This activity resulted in an 8 km long NW- trending surface rupture and caused minor structural damages in the nearby town of Al-Ays where about 40,000 inhabitants were evacuated (Pallister et al., 2010). This seismic swarm is considered as a manifes- tation of an aborted volcanic eruption where the diking event was located at about 2–5 km depth (Hansen et al., 2013). Harrat Lunayyir (Fig. 1) is considered as one of the youngest (<1Ma, Pallister et al., 2010) and the smallest volcanic lava felds in the Arabian Peninsula where recent basalt eruption products cover an approximate area of 3500 km 2 . The last eruption recorded in this area occurred ~ 1000 years ago (Camp et al., 1987). Before 2009, weak to moderate seismicity was observed in the area and it was mostly related to crustal * Corresponding author. E-mail address: mfbrahim@kau.edu.sa (M.F. Abdelwahed). Contents lists available at ScienceDirect Journal of Asian Earth Sciences journal homepage: www.elsevier.com/locate/jseaes https://doi.org/10.1016/j.jseaes.2022.105484 Received 29 January 2022; Received in revised form 30 October 2022; Accepted 7 November 2022