Supporting Data Repository for paper for What do P-wave Velocites Tell Us about the Critical Zone


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Created: Dec 13, 2021 at 4:59 p.m.
Last updated: Dec 13, 2021 at 6:21 p.m.
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Abstract

Fractures in Earth’s critical zone influence groundwater flow and storage and promote chemical weathering. Fractured materials are difficult to characterize on large spatial scales because they contain fractures that span a range of sizes, have complex spatial distributions, and are often inaccessible. Therefore, geophysical characterizations of the critical zone depend on the scale of measurements and on the response of the medium to impulses at that scale. Using P-wave velocities collected at two scales, we show that seismic velocities in the fractured bedrock layer of the critical zone are scale-dependent. The smaller-scale velocities, derived from sonic logs with a dominant wavelength of ~0.3 m, show substantial vertical and lateral heterogeneity in the fractured rock, with sonic velocities varying by 2,000 m/s over short lateral distances (~20 m), indicating strong spatial variations in fracture density. In contrast, the larger-scale velocities, derived from seismic refraction surveys with a dominant wavelength of ~50 m, are notably slower than the sonic velocities (a difference of ~3,000 m/s) and lack lateral heterogeneity. We show that this discrepancy is a consequence of contrasting measurement scales between the two methods; in other words, the contrast is not an artifact but rather information -- the signature of a fractured medium (weathered/fractured bedrock) when probed at vastly different scales. We explore the sample volumes of each measurement and show that surface refraction velocities provide reliable estimates of critical zone thickness but are relatively insensitive to lateral changes in fracture density at scales of a few tens of meters. At depth, converging refraction and sonic velocities likely indicate the top of unweathered bedrock, indicative of material with similar fracture density across scales.

DOI: 10.3389/frwa.2021.772185

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Resource Level Coverage

Spatial

Coordinate System/Geographic Projection:
WGS 84 EPSG:4326
Coordinate Units:
Decimal degrees
North Latitude
41.1850°
East Longitude
-105.3921°
South Latitude
41.1817°
West Longitude
-105.3993°

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Funding Agencies

This resource was created using funding from the following sources:
Agency Name Award Title Award Number
National Science Foundation (NSF) EPS-Q15 1208909
National Science Foundation (NSF) 1531313
National Science Foundation (NSF) EAR- 2012353

How to Cite

Flinchum, B. A. (2021). Supporting Data Repository for paper for What do P-wave Velocites Tell Us about the Critical Zone, HydroShare, http://www.hydroshare.org/resource/5c6dd575e27f44159f826e4c1c20bf19

This resource is shared under the Creative Commons Attribution CC BY.

http://creativecommons.org/licenses/by/4.0/
CC-BY

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