Shear-Wave Velocity Characterization of the USGS Hawaiian Strong-Motion Network on the Island of Hawaii and Development of an NEHRP Site-Class Map

Wong, Ivan G.; Stokoe, Kenneth H.; Cox, Brady R.; Yuan, Jiabei; Knudsen, Kathy L.; Terra, F. M.; Okubo, P.; Yin, Liang

doi:10.1785/0120100276

Cited by 23 publications

(28 citation statements)

References 12 publications

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“…Tropical saprolites typically have low shear wave velocities (V S ) of ~300 m/s (Yaede et al, 2015), corresponding to seismic design site class D (stiff soil; NEHRP, 2003). This is important in areas where there is a seismic hazard, like the Big Island of Hawaii (USA) (e.g., Wong et al, 2011). Chemical weathering of laterite substrates is an important long-term sink for atmospheric CO 2 (e.g., Dessert et al, 2003;Navarre-Sitchler and Brantley, 2007;Beaulieu et al, 2012;Nelson et al, 2013), thereby playing an important role in regulating the climate.…”

Section: Introductionmentioning

confidence: 99%

A conceptual model for the rapid weathering of tropical ocean islands: A synthesis of geochemistry and geophysics, Kohala Peninsula, Hawaii, USA

et al. 2018

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Much of the world's population lives in developing countries in regions with deeply weathered soils and thick, subjacent saprolites. These areas are widespread in the tropics and compose an important component of the critical zone (CZ). The Hawaiian Islands (USA) make an excellent natural laboratory for examining the tropical CZ, where the bedrock composition (basalt) is nearly uniform but of variable age and where climate (rainfall) varies greatly. The purpose of this study is to develop a model for rapid weathering to deep regolith profiles in tropical ocean islands.In the Kohala Peninsula, Hawaii, a variably weathered, thick soil and saprolite profile is exposed along sea cliffs in a mesic climate setting. Laterite development includes the entire vadose zone, with a mineralogy that chiefly includes halloysite ± gibbsite and Fe-oxides and mixed Fe-oxides and hydroxide species developed on a 303 ka substrate. Gibbsite-rich horizons occur in enhanced zones of weathering. At the base of the weathering front and on the rinds of core stones, transient smectite clays are developed, but rapidly break down to halloysite. Excess Al and Fe found in soil and saprolite likely originated from the decomposition of volcanic ash deposited on the ground surface from later effusive volcanism.Shear-wave velocity data derived from multichannel analysis of surface waves (MASW) and common depth point (CDP) seismic reflection profiles reveal important internal details of the weathering profiles that complement information derived from nearby rock outcrop along a sea cliff. In addition to identifying the depth of the weathering front, stiff horizons within the laterite correlate to high gibbsite abundances in the MASW profile. Parallel to the paleo-lava flow direction, relict igneous stratigraphy is expressed as seaward-dipping reflectors on CDP profiles, whereas perpendicular to flow, reflector geometry suggests lenticular bodies within laterite.A synthesis of geochemistry and geophysical studies leads to the development of a conceptual model to explain variable weathering within the CZ. First, although there is an overall trend for the downward migration of the weathering front with time, zones of high initial permeability (rubble above or below a'a flows; tephra or scoria deposits) are influenced by both downward and lateral fluxes of water, leading to enhanced weathering in what are now gibbsite-rich horizons. Second, the dense cores of a'a flows with widely spaced joints preserve large core stones that weather inward where halloysite-rich saprolite gives way to smectite-rich rims. Thus, differential weathering is a natural consequence of textural variations in primary igneous stratigraphy with superimposed additions of Al and Fe from the dissolution of basaltic glass. This study shows how weathering features and processes may be synthesized from outcrop, geochemical observations, and geophysical profiles into a multi-stage conceptual model of weathering.

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Section: Introductionmentioning

confidence: 99%

A conceptual model for the rapid weathering of tropical ocean islands: A synthesis of geochemistry and geophysics, Kohala Peninsula, Hawaii, USA

et al. 2018

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“…Three lines of evidence lead us to interpret the maximum seismic velocities in Kohala as representing chemically unaltered, but fractured or vesicular rock at depth. First, our maximum V s velocities are equivalent to previously reported ‘unweathered basalt’ S‐wave velocities for the Kohala peninsula (670 m/s, Wong et al ., ) based on a greater depth of investigation (up to 70 m depth) than presented in this study. The relative consistency of V p and V s as a function of depth for a constant V p / V s ratio, suggests that V p and V s are well correlated in this environment (Figure ) and gives us confidence in extrapolating the V s interpretation to the V p profiles.…”

Section: Seismic Characterization Of the Czmentioning

confidence: 77%

“…Dry sites (500–600 mm/yr) mean annual precipitation (MAP) show rapid increases in velocity with depth. These profiles reach unweathered basalt velocities (Wong et al ., ) at ~4–10 m depth. Sites with 1000 mm/yr MAP and greater display more gradual increase in velocity with depth and do not vary significantly with precipitation.…”

Section: Seismic Characterization Of the Czmentioning

confidence: 99%

Strong variation in weathering of layered rock maintains hillslope‐scale strength under high precipitation

Voigtlander

Clark

Zekkos

et al. 2018

Earth Surf Processes Landf

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The evolution of volcanic landscapes and their landslide potential are both dependent upon the weathering of layered volcanic rock sequences. We characterize critical zone structure using shallow seismic Vp and Vs profiles and vertical exposures of rock across a basaltic climosequence on Kohala peninsula, Hawai’i, and exploit the dramatic gradient in mean annual precipitation (MAP) across the peninsula as a proxy for weathering intensity. Seismic velocity increases rapidly with depth and the velocity–depth gradient is uniform across three sites with 500–600 mm/yr MAP, where the transition to unaltered bedrock occurs at a depth of 4 to 10 m. In contrast, velocity increases with depth less rapidly at wetter sites, but this gradient remains constant across increasing MAP from 1000 to 3000 mm/yr and the transition to unaltered bedrock is near the maximum depth of investigation (15–25 m). In detail, the profiles of seismic velocity and of weathering at wet sites are nowhere monotonic functions of depth. The uniform average velocity gradient and the greater depths of low velocities may be explained by the averaging of velocities over intercalated highly weathered sites with less weathered layers at sites where MAP > 1000 mm/yr. Hence, the main effect of climate is not the progressive deepening of a near‐surface altered layer, but rather the rapid weathering of high permeability zones within rock subjected to precipitation greater than ~1000 mm/yr. Although weathering suggests mechanical weakening, the nearly horizontal orientation of alternating weathered and unweathered horizons with respect to topography also plays a role in the slope stability of these heterogeneous rock masses. We speculate that where steep, rapidly evolving hillslopes exist, the sub‐horizontal orientation of weak/strong horizons allows such sites to remain nearly as strong as their less weathered counterparts at drier sites, as is exemplified by the 50°–60° slopes maintained in the amphitheater canyons on the northwest flank of the island. Copyright © 2017 John Wiley & Sons, Ltd.

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“…1). These high accelerations may be due to impedance contrasts in the velocity profile of the surficial layers in these areas (see Table 1; Wong et al, 2011).…”

Section: The Kiholo Bay Earthquake and The Triggered Landslidesmentioning

confidence: 99%

“…The higher amplitude of the observations is attributed to lower rigidity sediments at the North Kohala Police Station that are not in our 3D velocity model. We can estimate the effect of these sediments using the shallow shear-wave velocity profile available for this location (Wong et al, 2011) and given in Table 1. Figure 8 shows the SH response for this velocity profile with a Q S of 100 for all layers.…”

Section: Ground-motion Modelmentioning

confidence: 99%

Relation of Landslides Triggered by the Kiholo Bay Earthquake to Modeled Ground Motion

Harp¹,

Hartzell²,

Jibson³

et al. 2014

Bulletin of the Seismological Society of America

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The 2006 Kiholo Bay, Hawaii, earthquake triggered high concentrations of rock falls and slides in the steep canyons of the Kohala Mountains along the north coast of Hawaii. Within these mountains and canyons a complex distribution of landslides was triggered by the earthquake shaking. In parts of the area, landslides were preferentially located on east-facing slopes, whereas in other parts of the canyons no systematic pattern prevailed with respect to slope aspect or vertical position on the slopes. The geology within the canyons is homogeneous, so we hypothesize that the variable landslide distribution is the result of localized variation in ground shaking; therefore, we used a state-of-the-art, high-resolution ground-motion simulation model to see if it could reproduce the landslide-distribution patterns. We used a 3D finiteelement analysis to model earthquake shaking using a 10 m digital elevation model and slip on a finite-fault model constructed from teleseismic records of the mainshock. Ground velocity time histories were calculated up to a frequency of 5 Hz. Dynamic shear strain also was calculated and compared with the landslide distribution. Results were mixed for the velocity simulations, with some areas showing correlation of landslide locations with peak modeled ground motions but many other areas showing no such correlation. Results were much improved for the comparison with dynamic shear strain. This suggests that (1) rock falls and slides are possibly triggered by higher frequency ground motions (velocities) than those in our simulations, (2) the groundmotion velocity model needs more refinement, or (3) dynamic shear strain may be a more fundamental measurement of the decoupling process of slope materials during seismic shaking.

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Shear-Wave Velocity Characterization of the USGS Hawaiian Strong-Motion Network on the Island of Hawaii and Development of an NEHRP Site-Class Map

Cited by 23 publications

References 12 publications

A conceptual model for the rapid weathering of tropical ocean islands: A synthesis of geochemistry and geophysics, Kohala Peninsula, Hawaii, USA

A conceptual model for the rapid weathering of tropical ocean islands: A synthesis of geochemistry and geophysics, Kohala Peninsula, Hawaii, USA

Strong variation in weathering of layered rock maintains hillslope‐scale strength under high precipitation

Relation of Landslides Triggered by the Kiholo Bay Earthquake to Modeled Ground Motion

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