Seismicity Associated With the Formation of a New Island in the Southern Red Sea

Jade H W Eyles,Finnigan Illsley-Kemp,Joël Ruch,Sigurjón Jónsson,Derek Keir

doi:10.3389/feart.2018.00141

Abstract

Volcanic eruptions at mid-ocean ridges are rarely witnessed due to their inaccessibility, and are therefore poorly understood. Shallow waters in the Red Sea allow the study of ocean ridge related volcanism observed close to sea level. On the 18th December 2011, Yemeni fishermen witnessed a volcanic eruption in the Southern Red Sea that led to the formation of Sholan Island. Previous research efforts to constrain the dynamics of the intrusion and subsequent eruption relied primarily on interferometric synthetic aperture radar (InSAR) methods, data for which were relatively sparse. Our study integrates InSAR analysis with seismic data from Eritrea, Yemen, and Saudi Arabia to provide additional insights into the transport of magma in the crust that fed the eruption. Twenty-three earthquakes of magnitude 2.1–3.9 were located using the Oct-tree sampling algorithm. The earthquakes propagated southeastward from near Sholan Island, mainly between December 12th and December 13th. The seismicity is interpreted as being induced by emplacement of a ∼12 km-long dike. Earthquake focal mechanisms are primarily normal faulting and suggest the seismicity was caused through a combination of dike propagation and inflation. We combine these observations with new deformation modeling to constrain the location and orientation of the dike. The best-fit dike orientation that satisfies both geodetic and seismic data is NNW-SSE, parallel to the overall strike of the Red Sea. Further, the timing of the seismicity suggests the volcanic activity began as a submarine eruption on the 13th December, which became a subaerial eruption on the 18th December when the island emerged from the beneath the sea. The new intrusion and eruption along the ridge suggests seafloor spreading is active in this region.

Highlights

Magma motion through the crust can induce earthquakes, the analysis of which is a useful tool to understand when, where, and how magma is transported
We analyse a swarm of earthquakes in the Red Sea at 15– 15.2◦N and 42–42.3◦E, associated with a subaerial volcanic eruption starting on the 18th December 2011 that resulted in the formation of Sholan Island
The rapid migration of earthquakes, coupled with earthquakes focused at the lateral tips of the cluster after migration stops strongly suggests the earthquakes are caused by an intrusion that fed the eruption, broadly consistent with surface deformation patterns best modeled using the presence of a dike

Summary

Introduction

Magma motion through the crust can induce earthquakes, the analysis of which is a useful tool to understand when, where, and how magma is transported. The understanding of magma intrusion and volcanism is key for understanding dynamic processes that occur at divergent boundaries (e.g., Ebinger et al, 2013; Pagli et al, 2015; Ruch et al, 2016; Wilcock et al, 2016). Three sub-aerial volcanic eruptions have occurred in the last decade: on Jebel at Tair island (2007) and two eruptions resulting in the formation of Sholan Island (2011) and Jadid Island (2013) (Jónsson and Xu, 2015). All the islands lie on the rift axis of the Southern Red Sea. The eruptions of Jebel at Tair and Jadid lasted 8 and 2 months, respectively, and followed short duration (days) low magnitude (M > 4) seismic swarms thought to be caused by the intrusion of magma through the crust to the Earth’s surface (Xu et al, 2015). The eruption of Jebel at Tair was subaerial, while the first half of the Jadid eruption was submarine (Xu et al, 2015)

Results

Discussion

Conclusion