Seismic structure of the lithosphere from teleseismic converted arrivals observed at small arrays in the southern Sierra Nevada and vicinity, California

Abstract

Abstract. 21 well-distributed teleseisms (30 ø to 100 ø distance) were recorded by mixed broadband (BB) and short-period (SP) seismic arrays at Mineral King (MK) and Horseshoe Meadow (HM) in the southern Sierra Nevada and at Darwin Plateau (DP) between the Inyo and Argus ranges. These arrays permit identification and separation of direct P and S arrivals, reflections from topography, scattered energy, and arrivals from different back azimuths (multipath arrivals). P-to-S conversions can be identified from beamed BB or SP seismograms. Least squares time domain processing recovered single-event receiver functions from these beamed seismograms. Converted phases attributable to the Moho are clear and uncomplicated at DP; Ps-P times of 3.9-4.2 s correspond to crustal thicknesses of 31-33 km, assuming a mean P crustal velocity of 6.2 km/s and a Poisson's ratio (v) of 0.255. Ps-P times at HM (eastern Sierra) are 3.9-4.6 s (32-37 km) excepting some unusual seismograms from events at back azimuths of 2250-239 ø. MK (western Sierra) times for Ps-P show a strong E-W asymmetry: 3.9-4.1 s (31-33 kin) from the east, and 4.8-5.3 s (39-42 km) from the west. The MK arrivals from the east are multiple and substantially weaker by comparison with HM and DP. These results confirm the absence of a thick crust under the southern High Sierra inferred from both a refraction experiment coincident with this experiment and some earlier studies. At DP the Moho event follows an intracrustal negative polarity event defining the top of an S wave low-velocity zone. This feature dips west under the Sierran crest at HM but is absent farther west at MK. This feature appears to be a manifestation of extensional strain and thus indicates that the surficially undeformed Sierra overlies a tectonized lower crust. Sub-Moho energy is absent under the Basin and Range (DP) but is conspicuous under the High Sierra at positive arrivals -7.3 s (MK) and -9 s (HM) after the P. These arrivals might be from the base of a low-velocity, low-density upper mantle body supporting the Sierra.

Role of a phase: Change Moho in stabilization and preservation of the Southern Uralide orogen, Russia

“…However, in contrast with the compensation model proposed for the Sierra Nevada, where the high ele vations may be supported by low density bodies in the upper mantle [e.g., Ducea and Saleeby, 1996;Jones and Phinney, 1998], we suggest that the low elevations of the Southern Uralides resulted from high density material in the upper mantle, specifically eclogite facies assemblages that perhaps served to stabilize the orogen.…”

“…While results from young mountain belts, such as the Sierra Nevada, suggest that high elevations may be supported by low density bodies in the upper mantle [e.g., Ducea and Saleeby, 1996;Jones and Phinney, 1998], analyses of older mountain belts document various mechanisms for isostatic compen sation. Seismic profiles from the Archean age Baltic [BABEL Working Group, 1990] and Canadian [Henstock et al, 1998] shields suggested that they have been stable for over 1.5 Ga and still preserve their crustal roots as revealed by depressed Moho boundaries with significant relief.…”

Crustal thickness and images of the lithospheric discontinuities in the Gibraltar arc and surrounding areas

“…Energy on the transverse component is explained by lateral heterogeneity of the medium, in particular by dipping layers, azimuthal anisotropy or scattering (e.g. Cassidy 1992;Savage 1998;Jones & Phinney 1998). Even though, we observe features in the transverse components that can be explain by dipping layers or anisotropy, in this study we will only focus on the Q receiver functions to obtain crustal thickness values and leave the analysis of the transverse receiver components for a future study.…”

Electrical conductivity images of Quaternary faults and Tertiary detachments in the California Basin and Range

“…In addition to the geologic constraints, Foldout 1a shows downward projections to mid-crustal depths of the three major active fault zones on the basis of the MT data, as elaborated below. It also includes the position of the Moho (M), a lower crustal positive velocity anomaly (LCP) and a mid-crustal negative velocity anomaly (MCN) determined from analysis of teleseismic data [Jones and Phinney, 1998;R. A. Phinney, oral communication, 2001].…”

“…[3] The outstanding issues raised by this history include the hypothesis that removal of the upper crust over large areas in the Basin and Range was compensated by eastward flow of deep crust from beneath the Sierra Nevada [e.g., Wernicke, 1992] because the crustal thicknesses of unextended areas such as the Sierra Nevada and Inyo Mountains are roughly the same as that of the highly extended Death Valley region Fliedner et al, 1996;Jones and Phinney, 1998]. Further, controversy remains as to whether the strain pattern in the region results mainly from right-lateral strike-slip faulting or crustal extension.…”