Horizontal-to-Vertical Spectral Ratios and Refraction Microtremor Analyses for Seismic Site Effects and Soil Classification in the City of David, Western Panama
Abstract
:1. Introduction
2. Area of Study
2.1. Seismicity and Tectonics of the City of David and Surrounding Areas
2.2. Geological Context
3. Research Methodology
3.1. Microtremor’s Horizontal-to-Vertical Spectral Ratio
3.2. Liquefaction Vulnerability Index for Subsoil
3.3. Refraction Microtremor Method (ReMi) and Classification Using Vs30
3.4. Limitations of HVSR and ReMi Methods
4. Data Acquisition and Processing Strategy
4.1. HVSR
- The fundamental frequency of f0 must be greater than 10 divided by the window length of lw, for the peak to be significant;
- The significant cycles number must be greater than 200;
- HVSR curve standard deviation amplitude, at a range frequency of 0.5 f0 to 2 f0, must be <2 when f0 > 0.5 Hz, or < 3 when f0 < 0.5 Hz.
4.2. Multichannel Analysis of Surface Waves (MASW) and Vs30
5. Results
5.1. Spatial Distribution of H/V Spectral Ratios
5.2. Distribution of Vs30 Values from MASW Studies
6. Discussion
6.1. H/V Spectral Ratios
6.2. Results for Vs30
6.3. Comparison of Results from HVSR and ReMi
- First, stations located at the northern (R-6 and E17) and southern (R-1 and E01) ends of the city present no clear peaks according to SESAME [65] criteria (Type B). These stations happen to be located near the limits of Baru geological formation and other formations (i.e., Tonosi formation in the north and Las Lajas formation in the south). On the other hand, the rest of the stations fall clearly into the area corresponding to Baru formation. All of them exhibit clear peaks and, thus, are of Type A.
- Second, inspection of the shear wave velocity profiles for all the six ReMi stations allows us to infer that stations which presented velocity contrasts of ΔV ≥ 249 m/s at some depth can be associated with HVSR stations that exhibit clear peaks (HVSR curves of the Type A). In contrast, the stations that presented ΔV < 249 m/s are located close to HVSR stations with curves of Type B. This observation is in agreement with that presented by [11]. According to their research, whenever the HVSR peak is clear, then the site under study presents a large velocity contrast at some depth. They supported this fact with Fourier amplitude spectra computed from strong ground motion stations [11].
7. Conclusions
Author Contributions
Funding
Data Availability Statement
Acknowledgments
Conflicts of Interest
Appendix A. HVSR Spectra for Stations Described in Table 3
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Site/Class | Natural Period (s) | Predominant Frequency (Hz) |
---|---|---|
SC I: rock/stiff soil | TG < 0.2 | f0 > 5 |
SC II: rigid soil | 0.2 ≤ TG < 0.4 | 2.5 < f0 ≤ 5 |
SC III: semi-rigid soil | 0.4 ≤ TG < 0.6 | 1.6 < f0 ≤ 2.5 |
SC IV: soft soil | TG ≥ 0.6 | f0 ≤ 1.6 |
Soil Type | General Description | Vs30 (m/s) |
---|---|---|
A | Hard rock | Vs30 > 1500 |
B | Rock | 760 < Vs30 ≤ 1500 |
C | Hard and/or very stiff soil | 360 < Vs30 ≤ 760 |
D | Rigid soils | 180 < Vs30 ≤ 360 |
E | Semi-rigid soils | Vs30 < 180 |
F | Soils that require specific calculations | Does not apply |
Station | UTM Coordinates (m) | f0 (Hz) | A0 | Kg (Hz−1) |
---|---|---|---|---|
E01 | 341879 → 925069 | 6.5 | 1.7 | 0.4 |
E02 | 343069 → 926258 | 2.7 | 1.2 | 0.5 |
E03 | 342503 → 927833 | 4.2 | 2.1 | 1.1 |
E06 | 343863 → 925982 | 1.9 | 1.6 | 1.3 |
E07 | 343334 → 931171 | 11.0 | 1.7 | 0.3 |
E08 | 343541 → 926773 | 9.0 | 2.0 | 0.4 |
E09 | 341608 → 928320 | 3.4 | 1.4 | 0.6 |
E10 | 341903 → 931798 | 6.9 | 3.7 | 2.0 |
E11 | 344019 → 933809 | 11.0 | 1.3 | 0.2 |
E12 | 341807 → 933456 | 10.7 | 1.9 | 0.3 |
E13 | 343628 → 934452 | 7.0 | 2.2 | 0.7 |
E14 | 339485 → 929806 | 9.7 | 1.9 | 0.4 |
E15 | 342563 → 932566 | 8.6 | 2.7 | 0.8 |
E16 | 341238→931334 | 11.0 | 3.8 | 1.3 |
E17 | 343834 → 935632 | 9.9 | 1.7 | 0.3 |
E18 | 338409 → 931254 | 14.0 | 2.6 | 0.5 |
E19 | 342711 → 930259 | 7.4 | 2.7 | 1.0 |
E21 | 342349 → 935696 | 7.6 | 2.2 | 0.6 |
E22 | 344593 → 936622 | 13.6 | 1.1 | 0.1 |
E23 | 341328 → 929227 | 6.1 | 1.4 | 0.3 |
E24 | 343199 → 929526 | 11.0 | 2.3 | 0.5 |
E29 | 340856 → 930933 | 6.7 | 2.2 | 0.7 |
No. | Criterion | Range | Reliable |
---|---|---|---|
1 | f0 > 10/lw | [1.9–14.4 Hz] > 0.4 Hz | Ok |
2 | nc > 200 | [2517–17,120] > 200 | Ok |
3 | σA < 2 | [0.23–1.31] < 2 | Ok |
Station | UTM Coordinates (m) | Vs30 (m/s) | Soil Classification |
---|---|---|---|
R-1 | 341914 → 925077 | 259 ± 1 | D |
R-2 | 342869 → 928047 | 369 ± 7 | C |
R-3 | 342392 → 930351 | 300 ± 15 | D |
R-4 | 342630 → 931976 | 335 ± 10 | D |
R-5 | 343689 → 933689 | 360 ± 4 | D |
R-6 | 343690 → 935579 | 319 ± 8 | D |
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Grajales-Saavedra, F.; Mojica, A.; Ho, C.; Samudio, K.; Mejía, G.; Li, S.; Almengor, L.; Miranda, R.; Muñoz, M. Horizontal-to-Vertical Spectral Ratios and Refraction Microtremor Analyses for Seismic Site Effects and Soil Classification in the City of David, Western Panama. Geosciences 2023, 13, 287. https://doi.org/10.3390/geosciences13100287
Grajales-Saavedra F, Mojica A, Ho C, Samudio K, Mejía G, Li S, Almengor L, Miranda R, Muñoz M. Horizontal-to-Vertical Spectral Ratios and Refraction Microtremor Analyses for Seismic Site Effects and Soil Classification in the City of David, Western Panama. Geosciences. 2023; 13(10):287. https://doi.org/10.3390/geosciences13100287
Chicago/Turabian StyleGrajales-Saavedra, Francisco, Alexis Mojica, Carlos Ho, Krysna Samudio, George Mejía, Saddy Li, Larisa Almengor, Roberto Miranda, and Melisabel Muñoz. 2023. "Horizontal-to-Vertical Spectral Ratios and Refraction Microtremor Analyses for Seismic Site Effects and Soil Classification in the City of David, Western Panama" Geosciences 13, no. 10: 287. https://doi.org/10.3390/geosciences13100287
APA StyleGrajales-Saavedra, F., Mojica, A., Ho, C., Samudio, K., Mejía, G., Li, S., Almengor, L., Miranda, R., & Muñoz, M. (2023). Horizontal-to-Vertical Spectral Ratios and Refraction Microtremor Analyses for Seismic Site Effects and Soil Classification in the City of David, Western Panama. Geosciences, 13(10), 287. https://doi.org/10.3390/geosciences13100287