Estimating earthquake source depths by combining surface wave amplitude spectra and teleseismic depth phase observations

Heyburn, Ross; Selby, Neil D.; Fox, Ben

doi:10.1093/gji/ggt140

“…Since the depth of an icequake is critical evidence for or against hydrofracture, a more accurate method is required for constraining hypocentral depth. We use surface wave information in the form of P to Rayleigh wave amplitude ratios to constrain hypocentral depth (Heyburn et al, 2013; Jia et al, 2017; Stein & Wiens, 1986; Tsai & Aki, 1970). Figure 1a shows finite‐difference full‐waveform modeling results (Larsen et al, 2001) and observations of P to Rayleigh amplitude ratios, plotted against epicentral distance for a range of crevasse depths.…”

Section: Resultsmentioning

confidence: 99%

Breaking the Ice: Identifying Hydraulically Forced Crevassing

Hudson

¹

,

Brisbourne

²

,

White

³

et al. 2020

Geophysical Research Letters

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Hydraulically forced crevassing is thought to reduce the stability of ice shelves and ice sheets, affecting structural integrity and providing pathways for surface meltwater to the bed. It can cause ice shelves to collapse and ice sheets to accelerate into the ocean. However, direct observations of the hydraulically forced crevassing process remain elusive. Here we report a novel method and observations that use icequakes to directly observe crevassing and determine the role of hydrofracture. Crevasse icequake depths from seismic observations are compared to a theoretically derived maximum dry crevasse depth. We observe icequakes below this depth, suggesting hydrofracture. Furthermore, icequake source mechanisms provide insight into the fracture process, with predominantly opening cracks observed, which have opening volumes of hundredths of a cubic meter. Our method and findings provide a framework for studying a critical process that is key for the stability of ice shelves and ice sheets and, therefore, future sea level rise projections.

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“…Since the depth of an icequake is critical evidence for or against hydrofracture, a more accurate method is required for constraining hypocentral depth. We use surface wave information in the form of P to Rayleigh wave amplitude ratios to constrain hypocentral depth (Heyburn et al, 2013;Jia et al, 2017;Stein & Wiens, 1986;Tsai & Aki, 1970). Figure 1a shows finite-difference full-waveform modeling results (Larsen et al, 2001) and observations of P to Rayleigh amplitude ratios, plotted against epicentral distance for a range of crevasse depths.…”

Section: Evidence For Dry Fracture Versus Hydrofracture From Crevasse Depthmentioning

confidence: 99%

Breaking the ice: Identifying hydraulically-forced crevassing

Hudson

¹

,

Brisbourne

²

,

White³

et al. 2020

Preprint

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Hydraulically forced crevassing is thought to reduce the stability of ice shelves and ice sheets, affecting structural integrity and providing pathways for surface meltwater to the bed. It can cause ice shelves to collapse and ice sheets to accelerate into the ocean. However, direct observations of the hydraulically forced crevassing process remain elusive. Here we report a novel method and observations that use icequakes to directly observe crevassing and determine the role of hydrofracture. Crevasse icequake depths from seismic observations are compared to a theoretically derived maximum dry crevasse depth. We observe icequakes below this depth, suggesting hydrofracture. Furthermore, icequake source mechanisms provide insight into the fracture process, with predominantly opening cracks observed, which have opening volumes of hundredths of a cubic meter. Our method and findings provide a framework for studying a critical process that is key for the stability of ice shelves and ice sheets and, therefore, future sea level rise projections.

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“…Craig [11] gave a general overview of the existing methods to estimate focal depth, which mainly contain waveform-based methods and traveltimebased methods. Heyburn et al [12] estimated focal depth by measuring both teleseismic depth phases pP and sP and surface wave amplitude spectra. Florez and Prieto [10] proposed an array processing technique to calculate focal depth using pP-P times and double-difference algorithm, which needs two close events.…”

Section: Introductionmentioning

confidence: 99%

Accurate Redetermination of the Focal Depth by Using the Time Intervals between the Inner Core Phases PKIKP and pPKIKP

Li

¹

,

Gao

²

,

Wang

³

et al. 2022

Applied Sciences

0

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The hypocenter parameters of an earthquake may give us an insight into the Earth’s structure and tectonic processes. Among the hypocenter parameters, the focal depth is normally more difficult to estimate than the earthquake location (latitude and longitude). We propose to use the pPKIKP-PKIKP arrival time intervals for estimating the focal depth. We analyze the sensitivity of the pPKIKP-PKIKP arrival time interval to the earthquake depth. We measure the pPKIKP-PKIKP arrival time interval on seismograms (the vertical component), and invert the time interval data set using the simulated annealing inversion algorithm. We illustrate the inversion approach on two teleseismic earthquakes which have shallow and deep focal depths, and demonstrate that the approach is indeed appropriate to the shallow and deep event. We can obtain a reliable estimate on focal depth, even though the seismic station is sparse or in a remote part of the epicenter.

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Estimating earthquake source depths by combining surface wave amplitude spectra and teleseismic depth phase observations

Cited by 11 publications

References 22 publications

Breaking the Ice: Identifying Hydraulically Forced Crevassing

Breaking the Ice: Identifying Hydraulically Forced Crevassing

Breaking the ice: Identifying hydraulically-forced crevassing

Accurate Redetermination of the Focal Depth by Using the Time Intervals between the Inner Core Phases PKIKP and pPKIKP

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