Geology topics

Makbule Ilgac

Publications and source records attributed to Makbule Ilgac.

3 recordsLinked to original sources

USGS2024

Are the horizontal-to-vertical spectral ratios of earthquakes and microtremors the same?

We consider the similarities and differences between earthquake and microtremor horizontal‐to‐vertical spectral ratios (eHVSR and mHVSR, respectively) using a dataset of 161 sites in southern California. Quantitative comparisons are made in terms of the eHVSR and mHVSR lognormal median curves, as well as the frequencies and amplitudes associated with the fundamental‐ and higher‐mode resonances where present. The results show only 58% of the eHVSR–mHVSR pairs agree in terms of their median curve and only 25% of the eHVSR–mHVSR pairs agree in terms of shared resonances, which increases to 68% if flat HVSRs are considered equivalent. Furthermore, while the shared resonances match very well in terms of frequency (root mean square error, RMSE, <0.11 Hz), the amplitudes of those resonances do not agree (RMSE >1.6). These findings demonstrate that while eHVSR and mHVSR agree at some sites, they are not equivalent at all sites. To investigate if the agreement between eHVSR and mHVSR could be related to features of the microtremor data, earthquake recordings, and/or the site conditions, three machine learning (ML) models at varying levels of interpretability are presented. The ML models—which include multivariate logistic regression, gradient‐boosted trees, and support vector machines—show only partial success at using site‐specific data to predict whether eHVSR and mHVSR will likely agree in terms of their median curve (accuracy of 78%) and number of resonances (accuracy of 84%). Therefore, we conclude that while eHVSR and mHVSR can be quite similar in terms of resonant frequencies at some sites, they are not identical at all sites. Furthermore, preliminary evidence shows that the agreement of eHVSR and mHVSR can be predicted a priori given features of the microtremor measurements, earthquake recordings, and site conditions, although a larger dataset will be necessary for developing a robust predictive model.

California↗

USGS2018

Examination of differences between three SPT-based seismic soil liquefaction triggering relationships

The preceding companion paper presented the updating of the seismic soil liquefaction triggering relationship of Cetin et al. [1], and compared the resulting updated relationship with the earlier version. In this second paper, a detailed cross-comparison is made between three triggering relationships: (1) Seed et al. [2], as slightly updated by the NCEER Working Group (Youd et al. [3]), (2) Boulanger and Idriss [4], and (3) Cetin et al. [5]. Differences between these three triggering relationships, and the apparent causes of them are examined. Also studied are the impacts of these differences on levels of conservatism with regard to evaluation of liquefaction triggering hazard, and the resulting risks for engineering projects.

Soil Dynamics and Earthquake Engineering↗

USGS2016

Summary of SPT based field case history data of CETIN (2016) database

This report provides documentation of the Cetin et al. (2016) field performance case histories, probabilistic maximum likelihood assessment and the sources of differences between the liquefaction triggering resistance estimations (CRR values) of the widely used liquefaction triggering relationships of Seed et al. (1985), Cetin et al. (2004, 2016) and Boulanger and Idriss (2012). Cetin et al. (2016-a) presented a concise summary of the improved database and the updated triggering relationships. For the sake of completeness, as part of Chapter 2 of this report, Cetin et al. (2016-a) manuscript is re-presented, as edited to include the electronic supplements, and a broader and more detailed documentation of all of case histories. This broader and more detailed documentation along with the interpretations of other researchers is presented in Appendix A. Similarly, site response analyses details and results from Cetin (2000) is re-presented in Appendix B. To enable the readers to quickly refer to Cetin and Seed (2004), it is also included in Appendix C. The sources of differences between the liquefaction triggering resistance estimations (CRR values) of the widely used liquefaction triggering relationships of Seed et al. (1985), Cetin et al. (2004) and Boulanger and Idriss (2012) were discussed in Cetin et al. (2016-b). Again, for the sake of completeness, as part of Chapter 3 of this report, Cetin et al. (2016-b) manuscript is re-presented, as edited to the include of electronic supplements, and a detailed response to issues addressed by Idriss and Boulanger (2012). Also, the technical response letter (Cetin, 2014) prepared at the request of the members of the NRC Committee on the State of the Art and Practice in Earthquake Induced Soil Liquefaction Assessment, is given in Appendix D, which is helpful to follow the technical discussions. This report is intended only as a concise summary of a vast amount of data. The interpretations presented are those of the research team. A more detailed description of some of the details of the methods and procedures used to evaluate and analyze these field performance case histories is also presented in Cetin (2000) and Cetin et al. (2000) though the final evaluations presented in this report are the most recent interpretations undertaken under these current studies.

Report↗