Seismic imaging of Santorini: Subsurface constraints on caldera collapse and present-day magma recharge

Hooft, E. E.; Heath, Benjamin; Toomey, D. R.; Paulatto, M.; Papazachos, C. B.; Nomikou, Paraskevi; Morgan, Joanna; Warner, Mike

doi:10.1016/j.epsl.2019.02.033

Cited by 39 publications

(47 citation statements)

References 71 publications

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“…Bathymetric and available tectonic data of the SATZ most recently published by Nomikou, Hübscher et al (2019) and Hooft et al (2017) reveal a system of ridges and basins which has been interpreted as an extensional complex of tectonic grabens and horsts. To the southwest, the SATZ is characterized by the volcanic centers of Christiana, Santorini, and Kolumbo, which are responsible for numerous volcanic eruptions, including the well‐known Minoan Eruption of Santorini approximately 3,600 years ago (Druitt & Francaviglia, 1992; Druitt et al, 1999; Hooft et al, 2019; Nomikou, Druitt et al, 2016). The remarkably linear alignment of the volcanic edifices highlights the fundamental control that crustal structure and tectonics have on the location of volcanic activity (Heath et al, 2019; Hooft et al, 2019; Nomikou, Hübscher et al, 2019; Nomikou et al, 2013).…”

Section: Geological Settingmentioning

confidence: 99%

“…Based on a recent active seismic tomography experiment, Heath et al (2019) and Hooft et al (2019) obtained tomographic P ‐wave velocity models for the upper crustal structure across Santorini Volcano and the surrounding region. In agreement with the previous tectonic models, they conclude that tectono‐magmatic lineaments control magma emplacement at Santorini and Kolumbo and that the initiation of basin formation predates the onset of volcanism.…”

Section: Geological Settingmentioning

confidence: 99%

“…Therefore, the only available velocity information from the SATZ are the tomographic P ‐wave velocity models presented by Heath et al (2019) and Hooft et al (2019). While these models are well suited to study the large‐scale structure of the upper <3‐km crust, they do not resolve the small‐scale velocity distribution and do not account for the high degree of local complexity in the rift basins.…”

Section: Imaging Challengesmentioning

confidence: 99%

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When There Is No Offset: A Demonstration of Seismic Diffraction Imaging and Depth‐Velocity Model Building in the Southern Aegean Sea

et al. 2020

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A vast majority of marine geological research is based on academic seismic data collected with single-channel systems or short-offset multichannel seismic cables, which often lack reflection moveout for conventional velocity analysis. Consequently, our understanding of Earth processes often relies on seismic time sections, which hampers quantitative analysis in terms of depth, formation thicknesses, or dip angles of faults. In order to overcome these limitations, we present a robust diffraction extraction scheme that models and adaptively subtracts the reflected wavefield from the data. We use diffractions to estimate insightful wavefront attributes and perform wavefront tomography to obtain laterally resolved seismic velocity information in depth. Using diffraction focusing as a quality control tool, we perform an interpretation-driven refinement to derive a geologically plausible depth-velocity model. In a final step, we perform depth migration to arrive at a spatial reconstruction of the shallow crust. Further, we focus the diffracted wavefield to demonstrate how these diffraction images can be used as physics-guided attribute maps to support the identification of faults and unconformities. We demonstrate the potential of this processing scheme by its application to a seismic line from the Santorini Amorgos Tectonic Zone, located on the Hellenic Volcanic Arc, which is notorious for its catastrophic volcanic eruptions, earthquakes, and tsunamis. The resulting depth image allows a refined fault pattern delineation and, for the first time, a quantitative analysis of the basin stratigraphy. We conclude that diffraction-based data analysis has a high potential, especially when the acquisition geometry of seismic data does not allow conventional velocity analysis. Plain Language Summary The active seismic method is a standard tool for studying and imaging the Earth's lithosphere. Proper imaging of complex geological targets requires seismic data of excellent quality, which are typically only acquired with expensive industrial surveys. Academic surveys, however, are often restricted to marine seismic equipment with limited illumination, which compromises imaging and interpretation. While most of the contemporary processing and interpretational routines are tailored to the reflected wavefield, recent research suggests that the often overlooked diffracted wavefield might help to overcome the gap between academic and industrial seismic imaging. Wave diffraction is the response of the seismic wavefield to small-scale subsurface structures and allows to estimate velocities even from single-channel seismic data. In this study, we use an academic seismic profile from the southern Aegean Sea and extract a rich diffracted wavefield from the data. We utilize these diffractions to estimate a velocity model that permits a reconstruction of the subsurface in depth and specifically highlight discontinuous features related to past dynamic processes. Such depth images allow us to reliably measure thicknesses and fault angles. We con...

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Section: Geological Settingmentioning

confidence: 99%

Section: Geological Settingmentioning

confidence: 99%

Section: Imaging Challengesmentioning

confidence: 99%

See 1 more Smart Citation

When There Is No Offset: A Demonstration of Seismic Diffraction Imaging and Depth‐Velocity Model Building in the Southern Aegean Sea

et al. 2020

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“…This interaction is also important for successful geothermal energy production in high-enthalpy volcanic systems (Reinsch et al, 2017). Seismic methods offer insights into the nature of these thermo-magmatic systems (e.g., Greenfield et al, 2016;Hooft et al, 2019;Wespestad et al, 2019). Seismicity indicates fluid movements through faults and conduits (e.g., Prejean et al, 2002;Hudson et al, 2017;Greenfield et al, 2019a), but can also be used to image their subsurface structure.…”

Section: Introductionmentioning

confidence: 99%

The Coupled Magmatic and Hydrothermal Systems of the Restless Aluto Caldera, Ethiopia

et al. 2020

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Seismicity can be used to better understand interactions between magma bodies, hydrothermal systems and their host rocks-key factors influencing volcanic unrest. Here, we use earthquake data to image, for the first time, the seismic velocity structure beneath Aluto, a deforming volcano in the Main Ethiopian Rift. Traveltime tomography is used to jointly relocate seismicity and image 3D P-and S-wave velocity structures and the ratio between them (V P /V S). At depths of 4-9 km, the seismicity maps the top of a large low velocity zone with high V P /V S , which we interpret as a more ductile and melt-bearing region. A shallow (<3 km) hydrothermal system exhibits low seismic velocities and very low V P /V S (∼1.40), consistent with the presence of gases exsolved from a deeper melt-rich mush body. The Artu Jawe fault and fracture system provides the migration pathway that connects the deeper mush body with the shallow hydrothermal system. Together, these observations demonstrate that the interaction between magmatic and hydrothermal systems, driven by the exchange of fluids, is responsible for the restless behavior of Aluto.

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“…Near‐surface low‐velocity, low‐density layers are known to exist at caldera‐type volcanic systems and are interpreted as sediments and porous caldera fill deposits (Heath et al, 2015; Hooft et al, 2019) or results from hydrothermal alteration (Farrell et al, 2014). The presence of this layer close to the surface can dramatically affect the recorded signals.…”

Section: Resultsmentioning

confidence: 99%

Detectability of Melt‐Rich Lenses in Magmatic Reservoirs From Teleseismic Waveform Modeling

2020

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Seismic imaging is the most commonly used technique to constrain the size, geometry, and current state of active magma reservoirs in the Earth's crust. However, unequivocal detection of eruptible magma bodies (>0.5 melt fraction) have not been reported yet. In this study, using teleseismic waveform modeling applied to synthetic data, we investigate the limitations of seismic inversions on resolving idealized melt-rich layers with thicknesses smaller than the characteristic wavelength of the teleseismic waves. We show that inverting for melt-rich layers with thicknesses of about 0.2 km, consistent with the average thickness of erupted layers associated with voluminous caldera eruptions, yields significant underestimation of the inferred melt fractions and overestimation of the thickness of that layer. We further extend our synthetic tests to study the effect of noise, variable thickness of the input melt-rich layer, and different time windows from the seismograms on the quality of inverted parameters (thickness and melt fraction of the melt-rich layer). We find that (1) thicker melt-rich layers can be better resolved, (2) longer time windows (~4-6 s) from seismograms reduce the trade-off between melt fraction and layer thickness observed in the inversion results, and (3) noise emphasizes the melt fraction-thickness trade-off and leads to a bias toward thicker lower melt fraction layers retrieved from the inversions. Our synthetic study therefore supports that the lack of detection of melt-dominated horizons from seismic inversions does not preclude their existence and can be caused by a current limit in our ability to detect them.

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Seismic imaging of Santorini: Subsurface constraints on caldera collapse and present-day magma recharge

Cited by 39 publications

References 71 publications

When There Is No Offset: A Demonstration of Seismic Diffraction Imaging and Depth‐Velocity Model Building in the Southern Aegean Sea

When There Is No Offset: A Demonstration of Seismic Diffraction Imaging and Depth‐Velocity Model Building in the Southern Aegean Sea

The Coupled Magmatic and Hydrothermal Systems of the Restless Aluto Caldera, Ethiopia

Detectability of Melt‐Rich Lenses in Magmatic Reservoirs From Teleseismic Waveform Modeling

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