Shear-wave splitting variation over short spatial scales on continents

Helffrich, George; Silver, Paul G.; Given, Holly K.

doi:10.1111/j.1365-246x.1994.tb00142.x

Cited by 65 publications

(62 citation statements)

References 49 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…Quite often the station displaying seismic isotropy is located on a margin of a large tectonic unit such as a craton (e.g. SUR, South Africa, Hellfrich et al 1994 or MDVB, Vermont in this study) or a present-day plate (e.g. ORV, California, Savage & Silver 1993).…”

Section: Discussion a N D Conclusionmentioning

confidence: 99%

“…Our observations can be used to define three areas where the observed parameters of seismic anisotropy are coherent both in direction and amplitude. Such areas imply regions of similar elastic properties in the underlying mantle, and are sometimes referred to as anisotropic domains (Hellfrich et al 1994). Large (-1 s) values of S-wave splitting time and a westerly (260"-280") fast direction define a domain corresponding to cratonic North America.…”

Section: Discussion a N D Conclusionmentioning

confidence: 99%

“…A summary of shear-wave splitting measurements is given in Table 3. Following common practice (Silver & Chan 1991;Hellfrich, Silver & Given 1994), we designated observations of Table 2) and (b) Magnitude 8.0 Tonga earthquake (950407 in Table 2). …”

Section: Delays Are D U E To Anisotropymentioning

confidence: 99%

See 2 more Smart Citations

Seismic anisotropy in the north-eastern US as a source of significant teleseismicPtraveltime anomalies

Levin¹,

Menke²,

Lerner-Lam³

1996

Geophysical Journal International

View full text Add to dashboard Cite

S U M M A R YObservations of shear-wave splitting in the north-eastern US and southern Canada provide evidence for seismic anisotropy in the lithosphere throughout most of the region. S-wave splitting times of the order of 1 s are found within the Proterozoic Grenville Province and at a number of sites within the Appalachian Orogen. As a notable exception, seismic anisotropy is weak or absent in Vermont and western New Hampshire-a transitional zone between Proterozoic and Palaeozoic terranes. The fast direction is westerly (260"-280") within the Grenville Province, and north-westerly (300"-320") in the Appalachians. The effects of seismic anisotropy on the traveltimes of body waves are modelled in a horizontal layer characterized by an anisotropic elastic tensor of olivine. Simulations are made to study the influence of parameters such as the fraction of anisotropic material, the angle between the tensor symmetry axis and the wave propagation direction, and the type of crystallographic axis aligned in olivine grains. Results indicate that earth models with S-wave splitting times of about 1 s should also have P traveltime anomalies (positive or negative) of the order of 0.2-0.3 s. Also, alignment along either axis (a or b) can produce the combination of P delays between -0.25 and -0.75 s and S-wave splitting times between 0.7 and 1.3 s observed in the Adirondack Mountains. We conclude that velocity anomalies found in this region by earlier studies may in part be due to seismic anisotropy.

show abstract

Section: Discussion a N D Conclusionmentioning

confidence: 99%

Section: Discussion a N D Conclusionmentioning

confidence: 99%

See 1 more Smart Citation

Seismic anisotropy in the north-eastern US as a source of significant teleseismicPtraveltime anomalies

Levin¹,

Menke²,

Lerner-Lam³

1996

Geophysical Journal International

View full text Add to dashboard Cite

show abstract

“…On the other hand, variations in the splitting parameters often observed on a scale of a few hundred kilometres (Vinnik et a!. 1989b;Makeyeva et al 1992;Sandvol et al 1992;Savage & Silver 1993;Helffrich et al 1994) appear to rule out the contribution of the lower mantle. Nevertheless, it is not clear whether the source of anisotropy lies within the lithosphere or the sublithosphere.…”

Section: Introductionmentioning

confidence: 94%

Small-scale sublithospheric continental mantle deformation: constraints fromSKSsplitting observations

Alsina

Snieder

1995

Geophysical Journal International

174

140

View full text Add to dashboard Cite

It is generally believed that azimuthal seismic anisotropy is an important property of the subcontinental mantle, and that this is a relatively small-scale phenomenon compared with anisotropy of the oceanic mantle. During recent years, shear-wave splitting has come to be viewed as the most direct diagnostic of azimuthal anisotropy. The magnitude of the splitting delay times can often rule out a crustal source of anisotropy; however, it is not yet clear whether the source of anisotropy lies within the lithosphere or the sublithosphere. It is essential to know the scale of lateral variations and the distribution of anisotropy with depth in order to understand the origin of this phenomenon. Here we describe a way to constrain the depth of the anisotropy, by studying the lateral variation of the splitting parameters at neighbouring seismic stations. We use SKS and SKKS phases recorded at the NARS-NL array, a relatively dense network of broad-band stations separated by about 50 km. Fresnel zones at different depths are calculated for these phases. The depth of the anisotropy is constrained by the criterion that Fresnel zones corresponding to different splitting observations should not overlap. Variability in the splitting measurements for events with different directions of approach recorded at one station, and for single events recorded at various stations, provides evidence for a non-homogeneously distributed source of anisotropy, located below the array at different depths. We show that this variability in the measurements cannot be due to effects of crustal scattering. Our results indicate that the anisotropy is partly located in the sublithospheric mantle at about 400km depth. This suggests that the deformation in this region is subject to significant lateral variations.

show abstract

“…Eastern Snake River Plain splits are plotted as thick dark gray lines; other measured splits are shown with thin, solid lines; and null splits (only in Colorado and Kansas) are plotted as short light gray lines. [Split data from BOSTOCK and CASSIDY, 1995;SANDVOL et al, 1992;VINNIK et al, 1992;SILVER and CHAN, 1991;HELFFRICH et al, 1994;SILVER and KANESHIMA, 1993;RUPPERT, 1992;BARRUOL et al, 1996;OZALAYBEY and SAVAGE, 1995;SAVAGE et al, 1996]. anisotropy has been reset or erased.…”

Section: Figure 10mentioning

confidence: 99%

Anisotropy of the Yellowstone Hot Spot Wake, Eastern Snake River Plain, Idaho

Schutt

Humphreys

Dueker

1998

Pure and Applied Geophysics

View full text Add to dashboard Cite

Over the last 10 million years, the Yellowstone hot spot has passed beneath the eastern Snake River Plain, both magmatically modifying the Snake River Plain crust and creating a wider, wake-like ''tectonic parabola'' of seismicity and uplift. Analysis of SKS arrivals to a line array of 55 mostly broadband stations, distribution across the tectonic parabola, reveals a nearly uniform orientation of anisotropy, with an average fast axis orientation of N64E. The back azimuth of null splitting events is parallel to the measured fast axis, suggesting that anisotropic material consists of a single layer. Splitting parameters are independent of backazimuth, suggesting that anisotropy is constant beneath each station. Thus station-averaged split parameters are representative of the anisotropy beneath the station. Station-averaged split times range from 0.6-1.5 s, and define a pronounced depression in split times centered about 80 km southeast of the axis of the Snake River Plain.Assuming the degree of anisotropy (averaged over the ray path) to be no more than 10%, the split times are far too great for the anisotropy to be confined solely to the lithosphere. The simplest way to explain the observed anisotropy structure is to attribute it to simple shear strain caused by the absolute motion of North America. Because anisotropy is different in nearby Colorado and Nevada, we hypothesize that fossil anisotropy created in past orogens and continent-building events in the Snake River Plain area has been reset or erased by the passage of the hot spot, and that subsequent strain of the hot spot-related asthenospheric wake created a uniformly oriented fast axis. If this is true, then our array constrains the minimum of the hot spot's asthenospheric wake.

show abstract

Shear-wave splitting variation over short spatial scales on continents

Cited by 65 publications

References 49 publications

Seismic anisotropy in the north-eastern US as a source of significant teleseismicPtraveltime anomalies

Seismic anisotropy in the north-eastern US as a source of significant teleseismicPtraveltime anomalies

Small-scale sublithospheric continental mantle deformation: constraints fromSKSsplitting observations

Anisotropy of the Yellowstone Hot Spot Wake, Eastern Snake River Plain, Idaho

Contact Info

Product

Resources

About