Integrated Use of Seismograph and Strong-Motion Data to Determine Soil Amplification: Response of the Fraser River Delta to the Duvall and Georgia Strait Earthquakes
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Bibliographic record
Abstract
We present a new method to estimate site amplification, in which re- gional seismographic data are used to constrain the input motions to the soil profile. The amplification is determined as the ratio of the Fourier spec- trum of the recorded motion on soil to the spectrum of the inferred input motion at the underlying bedrock interface. The method is demonstrated for sites on the Fraser River Delta, British Columbia (B.C.), that recorded the 1996 M 5.1 Duvall, Wash- ington, and 1997 M 4.3 Georgia Strait, B.C., earthquakes. Regional seismographic recordings on rock sites are used to determine the apparent source spectra of these events. These spectra are attenuated to sites in the Fraser River Delta, then input to a specified soil profile. We compare the empirical-inferred amplification to alternative estimates of the soil amplification based on (1) the quarter-wavelength approach and (2) the assumption that the amplification is approximately equal to the observed H/V ratio. The empirical-inferred amplification estimates are grossly consistent with the theoretical amplification estimates, but have larger peaks at specific frequencies, probably due to resonant effects not accounted for in the quarter-wavelength ap- proach. The H/V ratio appears to be a simple and useful first approximation to the site response. The Fraser River Delta amplifies weak motions by factors of three to six over a broad frequency range, from 0.2 to 4 Hz. High-frequency motions (f 10 Hz) are attenuated. The long-period amplifications pose a serious concern in the event of strong earthquake shaking from large earthquakes. A useful by-product of the analysis is the determination of apparent source spectra for the events. The apparent source spectrum of the Georgia Strait earthquake is in good agreement with the Brune point-source model, with a stress drop of approxi- mately 45 bars. The apparent source spectrum of the slightly larger Duvall earthquake is in reasonable agreement with the Brune model, with a stress drop of about 70 bars; however, for the Duvall earthquake there is evidence of a sag in spectral amplitudes, relative to the Brune model, at intermediate frequencies (0.3 to 1 Hz). This inter- mediate-frequency sag is an expected result of source complexity; it is well dem- onstrated by the broadband seismic data.
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Full frame distilled prediction
Teacher imitationNot calibrated prevalence, not ground truth. Human validation pending. Learned from the 10,348 direct Codex labels and 10,348 direct Gemma labels. Candidate is the union of thresholded teacher heads; consensus is their intersection. These outputs are machine_predicted_unvalidated and are not human labels or direct frontier model labels.
Codex and Gemma teacher scores by category
| Category | Codex | Gemma |
|---|---|---|
| Metaresearch | 0.001 | 0.000 |
| Meta-epidemiology (narrow) | 0.000 | 0.000 |
| Meta-epidemiology (broad) | 0.000 | 0.000 |
| Bibliometrics | 0.000 | 0.000 |
| Science and technology studies | 0.000 | 0.001 |
| Scholarly communication | 0.000 | 0.000 |
| Open science | 0.001 | 0.000 |
| Research integrity | 0.000 | 0.000 |
| Insufficient payload (model declined to judge) | 0.001 | 0.000 |
Machine scores (provisional)
The two teacher heads of the student model, read on this work. A score orders the frame for review; it never asserts a category, and the validation status ships verbatim with every row.
Baseline scores from an immature model (maturity gate not passed, 7 training rounds). Scores rank; they never assert a category.
score_only:v0-immature-baseline · verbatim from the scoring run: score_only means the number may rank works, and no category label ships from it