Magma reflection imaging in Krafla, Iceland, using microearthquake sources

Abstract

The details of magma plumbing beneath active volcanoes remain a major challenge in geochemistry, geophysics, and volcanic hazard evaluation. Here we apply a relatively novel variation of seismic interferometry, which we call Virtual Reflection Seismic Profiling, to produce a high‐resolution image of a known crustal magma body. The technique takes advantage of recent advances in both seismic instrumentation (dense arrays) and seismic analysis (seismic interferometry). We have applied this technique to data recently acquired at an iconic volcanic system, Krafla, which lies on the mid‐Atlantic ridge as exposed in northern Iceland. What make this particular site exceptional are encounters with rhyolitic magma in two drill holes, K‐39 and Iceland Deep Drilling Project‐1 (IDDP‐1). These known magma bodies represent a unique calibration opportunity for surface geophysical measurements of magma distribution at depth. In this study, we produced a stacked, seismic reflection section by applying common depth point processing techniques to virtual shot gathers derived from interferometry of P waves from microearthquakes generated by tectonic, magmatic, and/or geothermal activity. We observe a strong, coherent reflection on the seismic section at a travel time corresponding to the depth at which magma was encountered in the IDDP‐1 wellbore. We interpret this reflection to be from magma or magma‐related fluids. Additional coherent reflections may correspond to other components of the magma plumbing beneath Krafla. These results represent a promising new technique for structural imaging with natural sources that can be applied to a wide array of geologic and energy problems that involve natural or induced seismic clusters.

Enhanced Resolution of the Subducting Plate Interface in Central Alaska From Autocorrelation of Local Earthquake Coda

“…Such studies now routinely extract surface waves from ambient microseismic noise (e.g., Lin et al, ; Shapiro et al, ). Interferometry has also been applied in attempts to extract body waves from ambient noise (e.g., Draganov et al, ; Lin et al, ; Roux et al, ; Ryberg, ; Zhan et al, ), from discrete sources including in exploration seismology (e.g., Schuster, ; Wapenaar et al, ) and from local or teleseismic earthquake signals (e.g., Kim et al, ; Nakata et al, ; Ruigrok & Wapenaar, ). However, distinct boundaries have commonly been difficult to image in the body waves from these studies, particularly at depths of more than a few kilometers, so the method is not commonly used for such imaging.…”

Seismic interferometry applied to local fracture seismicity recorded at Planchón-Peteroa Volcanic Complex, Argentina-Chile

“…La ISmA es una herramienta robusta, de manera tal que ha sido aplicada con diferentes tipos de datos, en diferentesáreas y a distintas escalas; por ejemplo, esta técnica ha sido aplicada a fases globales y telesísmicas (aquellas que se propagan por el núcleo y el manto, respectivamente, antes de arribar a la estación) para obtener imágenes del subsuelo cortical a escala regional (Ruigrok and Wapenaar, 2012;Nishitsuji et al, 2016), a ondas P de microsismos para caracterizar el subsuelo volcánico somero (Kim et al, 2017), y a registros de ruido sísmico ambiental (Draganov et al, 2007b;Gorbatov et al, 2013;Boullenger et al, 2014;Oren and Nowack, 2017).…”

Seismic Detection of a Magma Reservoir beneath Turtle Island of Taiwan by S-Wave Shadows and Reflections

“…Then, the location of the partial melt-rich reservoir obtained by S-wave shadows is further confirmed by the strong S-waves reflected from the partial melt-rich reservoir. Although the P-wave seismic reflections have been employed to detect magma reservoirs in several places 10 – 12 , we focus on the S-wave reflections that might be more sensitive to the melt-rich reservoirs. Both S-wave shadows and strong reflections are simulated using some simplified 2-D structures to estimate the suitable location of the magma reservoir.…”