| Autor: |
Gauntlett, M., Hudson, T., Kendall, J.‐M., Rawlinson, N., Blundy, J., Lapins, S., Goitom, B., Hammond, J., Oppenheimer, C., Ogubazghi, G. |
| Předmět: |
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| Zdroj: |
Journal of Geophysical Research. Solid Earth; May2023, Vol. 128 Issue 5, p1-21, 21p |
| Abstrakt: |
Understanding the crustal structure and the storage and movement of fluids beneath a volcano is necessary for characterizing volcanic hazard, geothermal prospects and potential mineral resources. This study uses local earthquake traveltime tomography to image the seismic velocity structure beneath Nabro, an off‐rift volcano located within the central part of the Danakil microplate near the Ethiopia‐Eritrea border. Nabro underwent its first historically documented eruption in June 2011, thereby providing an opportunity to analyze its post‐eruptive state by mapping subsurface fluid distributions. We use a catalog of earthquakes detected on a temporary seismic array using machine learning methods to simultaneously relocate the seismicity and invert for the three‐dimensional P‐ and S‐wave velocity structures (VP, VS) and the ratio between them (VP/VS). Overall, our model shows higher than average P‐ and S‐wave velocities, suggesting the presence of high‐strength, solidified intrusive magmatic rocks in the crust. We identify an aseismic region of low VP, low VS, and high VP/VS ratio at depths of 6–10 km b.s.l., interpreted as the primary melt storage region that fed the 2011 eruption. Above this is a zone of high VS, low VP, and low VP/VS ratio, representing an intrusive complex of fractured rocks partially saturated with over‐pressurized gases. Our observations identify the persistence of magma in the subsurface following the eruption, and track the degassing of this melt through the crust to the surface. The presence of volatiles and high temperatures within the shallow crust indicate that Nabro is a viable candidate for geothermal exploration. Plain Language Summary: Understanding the structure of the crust and the distribution and movement of fluids beneath a volcano allows for the assessment of volcanic hazard, geothermal potential and possible mineral extraction. To identify different regions of the crust and differentiate between fluids, we use the fact that the speed of seismic waves depends on the material they are traveling through. For example, seismic waves will travel through magma (molten, or liquid, rock) at lower speeds than in the surrounding rock. The focus of this study is Nabro volcano in Eritrea, which erupted in 2011. We use earthquakes that have been automatically detected following the eruption to image the structure of the crust in the form of 3D variations in seismic wave speeds. This identifies a volume of magma stored at depths of 6–10 km below sea level, which fed the eruption. Above this, we observe a region of rocks that are likely remnants of earlier eruptions at Nabro, with fractures containing gases at high pressure. The source of this high pressure is the release of gas from the magma storage zone. The presence of hot fluids means Nabro could be used as a source of geothermal power in the future. Key Points: 3D seismic modeling reveals the structure of the magmatic and hydrothermal systems beneath Nabro volcano in EritreaThe primary melt storage region feeding the 2011 eruption is located at depths of 6–10 km below sea levelDegassing from the magma storage zone causes overpressure in partially saturated, fractured intrusive complex above [ABSTRACT FROM AUTHOR] |
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