Constraining Sedimentary Structure Using Frequency‐Dependent P Wave Particle Motion: A Case Study of the Songliao Basin in NE China

Abstract

Knowledge on sedimentary structure within a basin is of great importance for exploring petroleum resources and predicting strong ground motions caused by earthquakes. Although 3‐D seismic data acquisition is common nowadays in petroleum industry, it is still impossible to conduct dense 3‐D seismic surveys at a whole‐basin scale. Passive seismic imaging thus can play a significant role in obtaining large‐scale sedimentary structure of basins with a reasonably good resolution. Here we present a new method to estimate the sedimentary structure beneath a seismic station using frequency‐dependent nonlinear particle motion of the teleseismic P wave, that is, a delay in the P wave arrival time on the horizontal component. Forward modeling suggests that the delay time and its variations over frequency are caused by interference of the direct P wave with the P‐to‐S conversions at the base of the sediments as well as sediment reverberations, and hence can be used to constrain the thickness and seismic velocity of the sediments beneath the station. We further develop a 2‐D grid search technique to estimate the optimum sediment thickness (Z) and surface S wave velocity (β0) by minimizing the residuals between the observed and calculated apparent P wave splitting times. The grid search yields reasonably robust estimates of Z and β0, although it has some trade‐off between the two parameters in the case of thin and unconsolidated sediments. We apply the method to 30+ broadband stations inside the Songliao basin, and the estimated sedimentary structures beneath these stations agree well with previous results.

Joint Inversion of Rayleigh Wave Phase Velocity, Particle Motion, and Teleseismic Body Wave Data for Sedimentary Structures

“…This horizontal P wave delay results from the interference of the direct P wave with P ‐to‐ S conversion at the sediment base and sediment reverberations. Bao and Niu () found that the horizontal P wave delay time is a function of frequency and used this frequency‐dependent delay time to constraint the S wave velocity and thickness of the sediment. In this study, instead of using the frequency‐dependent delay times of the teleseismic P wave to constrain the thickness of sedimentary basins, we employ the cross‐convolution misfit function (Bodin et al, ; Menke & Levin, ) as part of the objective function in the joint inversion.…”

“…Bao and Niu (2017) found that the horizontal P wave delay time is a function of frequency and used this frequency-dependent delay time to constraint the S wave velocity and thickness of the sediment. This horizontal P wave delay results from the interference of the direct P wave with P-to-S conversion at the sediment base and sediment reverberations.…”

“…Both surface wave and body wave (BW) data have been used in resolving sedimentary structures beneath seismic stations. For example, the amplitude ratio of Rayleigh wave recorded by the vertical and radial components, known as the Z/H ratio, is very sensitive to sedimentary structures (e.g., Boore & Toksöz, 1969) and has been used to invert for sedimentary structure (e.g., Lin et al, 2012, Li et al, 2016 teleseismic P waves are another type of data that are sensitive to the velocity jump at the sediment base and have been used to invert for sediment thickness and velocity (Akuhara et al, 2019;Bao & Niu, 2017). A recent study (Phạm & Tkalčić, 2017) suggests that autocorrelation of the teleseismic P wave coda is a promising technique for mapping shallow seismic boundaries.…”

Observations and Modeling of Long‐Period Ground‐Motion Amplification Across Northeast China

“…As indicated by the spatial variability of site amplification shown in Figures 3 and 4, the areas with substantial amplification are strongly correlated with sedimentary structures. These basins are filled with unconsolidated sediments up to 4 km in thickness (Bao & Niu, 2017;Li et al, 2016). The low-velocity shallow deposits resting on metamorphic basement create a strong contrast in near-surface material properties and thus substantially shown for reference (magenta lines).…”

Sedimentary basins investigation using teleseismic P‐wave time delays

“…In particular, the arrival time of teleseismic P-waves recorded inside a sedimentary basin displays time delays and polarization that both strongly depend on the basin properties and topography (e.g. Schmandt and Clayton 2013;Hofstetter and Dorbath 2014;Bao and Niu 2017).…”