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Use of Weak Motion Data to Constrain Site-Specific Ground Motion Estimates

Description: 

With the increasing recognition of the importance of non-ergodic components in a seismic hazard analysis, it is becoming increasingly more important to obtain site-specific amplification functions along with their uncertainties. The most common approach is performing site response analyses backed by detailed site characterization with measures of uncertainty. However, even detailed site response is still associated with significant epistemic uncertainty. An alternative approach would be utilizing recorded ground motions recorded at the site, if any, to constrain site effects. This approach is only viable if sufficient records are available at the site, which is generally not the case. However, for a seismically active region (such as California), rate of occurrence of small magnitude earthquakes (i.e., M_w<4.5) can be high enough for weak ground motions to be recorded using a temporarily deployed station within a practical timeframe, especially for the design of critical structures. This then raises the question: Can weak ground motions resulting from small magnitude events be used to constrain site effects? This study attempts to answer this question by investigating weak ground motions recorded in California from earthquakes with magnitudes ranging from 2.5 to 4.5. Using the ground motion recordings near two sites in Northern California, a generalized inversion technique was used to constrain source, path, and site terms, from which the site-specific transfer function with measures of uncertainty was estimated. The estimated transfer functions were compared with analytical transfer functions computed using 1-D site response analyses for two stations. The analytical transfer functions at these sites are slightly larger than the empirically constrained counterparts, thus overpredicting ground motions. Single-station variability at these stations suggests the empirical transfer functions are stable when there are enough ground motion recordings at the site. The approach proposed in this study can be employed to empirically constrain site response using weak recorded ground motions.

Session: How Well Can We Predict Broadband Site-Specific Ground Motion and Its Spatial Variability So Far? - II

Type: Oral

Date: 5/1/2024

Presentation Time: 11:00 AM (local time)

Presenting Author: Balakumar

Student Presenter: Yes

Invited Presentation: 

Authors