HVSR MEASUREMENTS IN COMPLEX SEDIMENTARY ENVIRONMENT AND HIGHLY STRUCTURED RESONATOR TOPOGRAPHY – COMPARISONS WITH SEISMIC REFLECTION PROFILES AND GEOPHYSICAL BOREHOLE LOGS
Bibliographic record
Abstract
Over the last two decades, horizontal-to-vertical spectral ratio (HVSR) measurements from microtremor recordings have gained popularity for seismic microzonation and assessment of earthquake site characteristics such as fundamental frequency (or period). More recently, procedures have been described where empirical relationships are developed between the fundamental frequency and sediment thickness at regional sites where shear wave velocity depth functions are well understood and a simple 2-layer-model is a good approximation of the subsurface structure. In contrast however, in complex glacial stratigraphy, sediment types commonly vary drastically from very soft glaciomarine clay to overconsolidated till. We observe that these changes can lead to strong impedance contrasts and hence, resonating horizons well above bedrock can be resolved. Without a-priori knowledge, sediment thickness could be significantly under-estimated. We examine the frequency spectra of microtremor recordings in both simple and complex sedimentary settings at locations along high-resolution shear wave seismic reflection profiles and at continuously cored boreholes with shear wave velocity (Vs) profiles. Vs range from 80 – 2000 m/s within the unconsolidated sediment overburden. Our results indicate that resonator topography can have a significant impact on peak shape and amplitude. In relatively simple 2-layer cases, peak frequencies decrease and broaden over dipping resonators and even disappear over very steep resonator slopes, indicating that two- and three-dimensional subsurface resonator topography is highly influential on peak shape. Additionally, we present examples where sharp increases in shear wave velocity within the sediment column form strong resonating horizons, producing a high amplitude peak which does not necessarily correlate with the bedrock surface. Our results suggest that resonator topography and velocity structure need to be well understood by a practitioner before interpreting geological conditions from HVSR data.
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How this classification was reachedexpand
Full frame machine prediction
Teacher imitationNot calibrated prevalence, not ground truth. Human validation pending. The Gemma side is a direct model label for every work in the frame, read from the title-only record. The Codex side is a classifier learned from the 10,348 direct Codex labels and calibrated to design-weighted sample rates; fields without enough sample support carry no Codex call. Candidate is the union of the two sides; consensus is their intersection. These outputs are machine_predicted_unvalidated and are not human labels.
Distilled classifier scores by category (both heads)
| Category | Codex | Gemma |
|---|---|---|
| Metaresearch | 0.000 | 0.001 |
| Meta-epidemiology (narrow) | 0.000 | 0.000 |
| Meta-epidemiology (broad) | 0.000 | 0.000 |
| Bibliometrics | 0.001 | 0.001 |
| Science and technology studies | 0.000 | 0.000 |
| Scholarly communication | 0.000 | 0.000 |
| Open science | 0.000 | 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 itClassification
machine, unvalidatedMachine predicted; a candidate call from one source (direct Gemma or distilled Codex), not a consensus.
How this classification was reached, model by model and score by score, is at the end of the page under "How this classification was reached".