Frequency-dependent horizontal-to-vertical spectral ratios (HVSRs) of three-component recordings provide information on site resonant frequencies, which are potentially useful for predicting site response. We compute HVSRs from Fourier amplitude spectra (FAS) using a relational database for site data mainly in California. We investigate the consistency of HVSRs derived from microtremors using temporary and permanent instruments (mHVSRs), and earthquake recordings (eHVSRs). We find microtremors and earthquake recordings are consistent for 60% of sites, with both showing significant peaks at similar frequencies (<20% difference). We also compare mHVSRs derived from co-located temporary instruments (as would be used in a site characterization study) vs. permanent instruments (which could be applied to characterize ground motion stations) to evaluate the effectiveness of the latter, enabling us to query microtremors from permanent stations to boost the HVSR database. While eHVSRs can be measured from accelerometers, we find mHVSRs are reliably captured by accelerometers only in limited cases, even when utilizing 24-bit data recorders. This might be due to the relatively high intrinsic noise and low sensitivity of accelerometers. Therefore, our comparisons are made using seismometer (velocimeter) data, and we find about 75% consistency in this case. These findings are important to consider when contemplating the development or use of site response models derived from HVSR-based parameters such as site frequency. In engineering applications, these parameters will almost always be derived from mHVSRs. However, for model development, it is tempting to use eHVSRs, because such information is most widely available for ground motion stations. Because mHVSRs and eHVSRs do not always match, it may be important to derive models solely from mHVSRs to ensure consistency between parameters used in model development and forward applications. However, such models do not yet exist.
Consistency of earthquake and microtremor HVSRs derived for California sites
Zimmaro P.;
2021-01-01
Abstract
Frequency-dependent horizontal-to-vertical spectral ratios (HVSRs) of three-component recordings provide information on site resonant frequencies, which are potentially useful for predicting site response. We compute HVSRs from Fourier amplitude spectra (FAS) using a relational database for site data mainly in California. We investigate the consistency of HVSRs derived from microtremors using temporary and permanent instruments (mHVSRs), and earthquake recordings (eHVSRs). We find microtremors and earthquake recordings are consistent for 60% of sites, with both showing significant peaks at similar frequencies (<20% difference). We also compare mHVSRs derived from co-located temporary instruments (as would be used in a site characterization study) vs. permanent instruments (which could be applied to characterize ground motion stations) to evaluate the effectiveness of the latter, enabling us to query microtremors from permanent stations to boost the HVSR database. While eHVSRs can be measured from accelerometers, we find mHVSRs are reliably captured by accelerometers only in limited cases, even when utilizing 24-bit data recorders. This might be due to the relatively high intrinsic noise and low sensitivity of accelerometers. Therefore, our comparisons are made using seismometer (velocimeter) data, and we find about 75% consistency in this case. These findings are important to consider when contemplating the development or use of site response models derived from HVSR-based parameters such as site frequency. In engineering applications, these parameters will almost always be derived from mHVSRs. However, for model development, it is tempting to use eHVSRs, because such information is most widely available for ground motion stations. Because mHVSRs and eHVSRs do not always match, it may be important to derive models solely from mHVSRs to ensure consistency between parameters used in model development and forward applications. However, such models do not yet exist.I documenti in IRIS sono protetti da copyright e tutti i diritti sono riservati, salvo diversa indicazione.
