A deterministic and stochastic velocity model for the Salton Trough/Basin and Range transition zone and constraints on magmatism during rifting

Abstract

As a high resolution addition to the 1992 Pacific to Arizona Crustal Experiment (PACE), a 45‐km‐long deep crustal seismic reflection profile was acquired across the Chocolate Mountains in southeastern California to illuminate crustal structure in the transition between the Salton Trough and the Basin and Range province. The complex seismic data are analyzed for both large‐scale (deterministic) and fine‐scale (stochastic) crustal features. A low‐fold near‐offset common‐midpoint (CMP) stacked section shows the northeastward lateral extent of a high‐velocity lower crustal body which is centered beneath the Salton Trough. Off‐end shots record a high‐amplitude diffraction from the point where the high velocity lower crust pinches out at the Moho. Above the high‐velocity lower crust, moderate‐amplitude reflections occur at midcrustal levels. These reflections display the coherency and frequency characteristics of reflections backscattered from a heterogeneous velocity field, which we model as horizontal intrusions with a von Kármán (fractal) distribution. The effects of upper crustal scattering are included by combining the mapped surface geology and laboratory measurements of exposed rocks within the Chocolate Mountains to reproduce the upper crustal velocity heterogeneity in our crustal velocity model. Viscoelastic finite difference simulations indicate that the volume of mafic material within the reflective zone necessary to produce the observed backscatter is about 5%. The presence of wavelength‐scale heterogeneity within the near‐surface, upper, and middle crust also produces a 0.5‐s‐thick zone of discontinuous reflections from a crust‐mantle interface which is actually a first‐order discontinuity.

Continental rupture and the creation of new crust in the Salton Trough rift, Southern California and northern Mexico: Results from the Salton Seismic Imaging Project

“…Larkin et al . [] performed low‐resolution deep crustal seismic reflection imaging of the transitional crustal structure between the Salton Trough and the Basin and Range province. Brothers et al .…”

“…However, no Pn phase was recorded, and the profile along the axis of the Salton Trough was poorly resolved. Larkin et al [1996] performed low-resolution deep crustal seismic reflection imaging of the transitional crustal structure between the Salton Trough and the Basin and Range province. Brothers et al [2009Brothers et al [ , 2011 studied basin and fault architecture in the top~70 m in the Salton Sea using high-resolution chirp seismic reflection data.…”

Estimation of the correlation structure of crustal velocity heterogeneity from seismic reflection data

“…Extensive research on exposures of a variety of lower, middle and upper crystalline crustal rocks, as well as the analysis of deep borehole logs, have indicated that crustal seismic heterogeneity is often complex and hence most effectively characterized using stochastic approaches (Leary 1991; Holliger & Levander 1992; Holliger et al 1993; Holliger & Levander 1994; Levander et al 1994a; Wu et al 1994; Goff & Levander 1996; Holliger 1996; Larkin et al 1996; Holliger 1997; Dolan et al 1998). Specifically, sections of crust exposed at the earth's surface are often seen to consist of a complicated distribution of lithologies having self‐affine or fractal characteristics over a broad range of scales, whose structure is well described by parametric statistical models.…”

The effects of crustal heterogeneity on ray-based teleseismic imaging

“…The layers take the form of regions in which the characteristic lengths of the stochastic heterogeneities are fixed within a given layer, but differ from one layer to another. The general observation is that the characteristic scale of the stochastic heterogeneities decreases with depth (Holliger & Levander 1994; Larkin et al 1996; Larkin et al 1997).…”