2017 Hennes Lecture at University of Washington

The GIGGS group at the University of would like to invite everyone to join them at their annual Hennes Lecture.  It is being held on Friday May 26th from 4pm-7pm on the UW campus. The presentation will be given my Jonathan Stewart, Chair of Civil Engineering at UCLA.

Friday, May 26
Presentation: 4:00 – 5:00
Reception: 5:00 – 7:00 (snacks provided, and drinks available for purchase)
The lecture is on the UW campus, in the Husky Union Building (HUB) Room 145
The event is free to attend and RSVP is not needed.
Contact: Shane Joseph Markus markussh@uw.edu

Site response uncertainty and its implications for seismic risk characterization

Along with source and path effects, site response analysis is a vital component of earthquake ground motion characterization. Ground motion prediction equations (GMPEs) include terms for modeling site response that are based on simple metrics of site condition, such as the time-average shear wave velocity in the upper 30 m (VS30). Because site terms in GMPEs are derived from global databases, and are based on incomplete information on site conditions, their predictions represent average levels of site response conditional on VS30. Such predictions are referred to as ergodic.

Actual site response at a given site is likely to differ from this global average. Viewed in this context, the actual site response for a particular site and intensity measure is the sum in log units of the ergodic estimate from a global model and a (generally unknown) site term (denoted hS). If the level of site-specific error (hS) can be identified and used to adjust the ergodic model, the ground motion analysis is more accurate (i.e., bias is removed) and the dispersion of the predicted ground motions is reduced. Therefore, site-specific evaluations of site response are useful and will often reduce mean hazard levels at long return periods (due to dispersion reduction), although uncertainty in the site response is considered in an epistemic manner.

Important questions pertaining to this process include how should these evaluations be performed, how reliable are the resulting site response estimates, and how can the results be used in a probabilistically rigorous manner as required for hazard- or risk-based applications?

With this in mind, the presentation will cover:

  1. The physical processes responsible for site effects;
  2. The manner by which these processes are (or are not) reflected in relatively generic site factors used in GMPEs and in building codes;
  3. Effectiveness of site-specific geotechnical ground response analyses to estimate site effects;
  4. Recommended procedures for evaluating site-specific site response and its implementation in hazard/risk characterization for critical facilities.