Use of small-scale liquefaction features to assess paleoseismicity: an example from the Saline River fault zone, Southeast Arkansas, USA

Randel T Cox,Shannon A Mahan,Christopher Lowe,Yanjun Hao

doi:10.3389/feart.2014.00031

Randel T Cox, Shannon A Mahan + Show 2 more

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https://doi.org/10.3389/feart.2014.00031

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Abstract

Large-scale liquefaction features (e.g., sand blows, lateral-spread fissure vents) that can be recognized on remote-sensing imagery and photography have been of great utility in developing chronologies of paleo-earthquakes. In areas where large-scale features are obscured on imagery by forest cover and Holocene exposure is lacking, small-scale liquefaction features (e.g., convoluted bedding, clastic intrusions, foundered and suspended blocks, water-escape structures) offer an alternative data source that can be investigated in meter-scale excavations. In order to assess the geographic extent of Holocene sand blow fields in southeast Arkansas that were previously mapped on river terraces and flood plains using aerial photography, we investigated the distribution of small-scale liquefaction features in alluvium along streams within a forested region between the sand blow fields. Our results suggest that the fields are not continuous and do not reflect a single large liquefaction field related to paleo-earthquakes >M 6.5. Features at one of our sites suggests the Desha County sand blow field may be larger than presently mapped, and that the distance from the center of the field to the farthest liquefaction may be ~30 km. The empirical relationship of magnitude and distance to farthest liquefaction suggests a field of this size could have been produced by a M 6.3 earthquake. We also found Holocene liquefaction features that we interpret as resulting from ground shaking near previously documented Pleistocene and Holocene surface ruptures of the Saline River fault zone. Liquefaction during a paleo-earthquake (~M 5.5) may have coincided with movement on that fault zone ~ AD 1700.

Highlights

The spatial distribution and recurrence intervals of large intraplate earthquakes in eastern North America are poorly understood, and some areas of significant seismic hazard have yet to be adequately characterized
At our field sites in the central and upstream reaches of streams that drain areas with sand-and-gravel-bearing Eocene and Pleistocene substrates, Holocene alluvium is composed of stratified, unconsolidated gravel, sand, silt, and clay that we assess as having high liquefaction potential
We interpret these features to have formed through liquefaction of alluvial sediment during strong ground shaking because they conform to the criteria for recognition of seismically-triggered liquefaction, because they are geographically and temporally clustered, and because they are found near a Holocene fault in the Saline River fault zone (Wheeler, 2002; Counts and Obermeier, 2012)

Summary

Introduction

The spatial distribution and recurrence intervals of large intraplate earthquakes in eastern North America are poorly understood, and some areas of significant seismic hazard have yet to be adequately characterized. Geodetic surveys (Meade, 1975; Officer and Drake, 1981; Calais et al, 2006) and geomorphic studies (Schumm et al, 1982; Burnett and Schumm, 1983; Cox, 1994) provide evidence of Quaternary and ongoing uplift and ground tilting in the region. This deformation has been inferred to be related to movements on the Saline River fault zone (Figure 1). Mapping of paleochannels and alluvial terraces associated with the Arkansas, Ouachita, and Saline Rivers indicates late Quaternary westward (up-dip) channel migration across eastward dipping strata of the Mississippi embayment (Schumm et al, 1982; Burnett and Schumm, 1983; Cox, 1994), and Pleistocene and Holocene alluvium is faulted and warped along these river alignments (Cox et al, 2000, 2012).

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