Non-Invasive Subsurface Site Characterization for Seismic Ground Response Analyses

Featuring Dr. Brady Cox, Utah State University

The importance of accurately predicting site effects for engineering infrastructure projects in seismically active regions cannot be overstated.

Numerical earthquake wave propagation simulations, known as ground response analyses (GRAs), are commonly performed in an attempt to estimate the site-specific, frequency-dependent amplification of seismic waves (i.e., site effects) as they travel from a reference bedrock condition up through soil layers to the ground surface.

One-, two-, and three-dimensional (1D, 2D, and 3D) GRAs have been developed. However, recent studies have revealed that recorded ground motions at more than 50% of borehole array sites are modeled using 1D GRAs. While 3D GRAs are theoretically plausible, they remain largely inaccessible due to a lack of adequate and affordable site characterization methods that can be used to develop 3D subsurface shear wave velocity (Vs) models down to depths required for ground response studies.

In this presentation, Dr. Brady Cox will detail several seismic site characterization methods usable in developing subsurface models for use in 1D, 2D and 3D GRAs. Dr. Cox will discuss methods such as horizontal-to-vertical spectral ratios (HVSR or H/V) of ambient noise, multi-channel analysis of surface waves and microtremor array measurement.

Additionally, a new geostatistical approach that can be used for building large pseudo-3D Vs models as a means to rationally account for spatial variability in GRAs will be presented. Each of these methods will be discussed from the perspective of case history applications, including comparisons between recorded and GRA-predicted ground motions at several borehole array sites.

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A New Way Of Maximum Magnitude Estimate for Induced Seismicity – Chaos

A New Way Of Maximum Magnitude Estimate for Induced Seismicity – Chaos

Traffic Light Systems (TLS) for induced seismicity by underground injections traditionally rely on magnitude thresholds. The choice of these thresholds is debated and found inappropriate, with most recent 2020 fashion proposing very low thresholds based on empirical observations.

In this session, Dr. Leo Eisner will demonstrate that these observations can be explained as order of statistics and show how this theory can be used for TLS.

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Review of Recent Applications of Ambient Noise Surface Wave Tomography (ANSWT)

Featuring Dan Hollis

Ambient seismic noise surface wave tomography for subsurface imaging and monitoring was developed in the early 2000s. Application of the method started with crustal studies and has evolved over the past several years to several applications: seismic hazard assessment, mineral exploration and development, Oil/Gas/Energy exploration and development, geotechnical assessment, and geothermal exploration and development.

In this session, special guest speaker, Dan Hollis will present a review of the ANSWT method and review several imaging and monitoring projects performed over the past couple of years.

This informative webinar + Q&A is a must-see!

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Surface Wave Methods for Seismic Site Characterization

Featuring Dr. Sebastiano Foti 

Surface wave methods gained in the past decades a primary role in many seismic projects. Specifically, they are often used to retrieve a 1D shear wave velocity model or to estimate the V_S,30 at sites of strong motion networks. The complexity of the interpretation process and the variety of possible approaches to surface wave analysis make it very hard to set a fixed standard to assure quality and reliability of the results.

In this session, special guest speaker Dr. Sebastiano Foti will introduce us to surface wave analysis and summarize the InterPACIFIC (Intercomparison of Methods for Site Parameter and Velocity Profile Characterization) guidelines published in 2018 and will provide some application examples.

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