Geology topics

Pengfei Wang

Publications and source records attributed to Pengfei Wang.

4 recordsLinked to original sources

USGS2021

Relational database for horizontal‐to‐vertical spectral ratios

Frequency‐dependent horizontal‐to‐vertical spectral ratios (HVSRs) of Fourier amplitudes from three‐component recordings can provide useful information for site response modeling. However, such information is not incorporated into most ground‐motion models, including those from Next‐Generation Attenuation projects, which instead use the time‐averaged shear‐wave velocity ( ⁠ V S "> V S VS ⁠ ) in the upper 30 m of the site and sediment depth terms. To facilitate utilization of HVSR, we developed a publicly accessible relational database. This database is adapted from a similar repository for V S "> V S VS data and provides microtremor‐based HVSR data (mHVSR) and supporting metadata, but not parameters derived from the data. Users can interact with the data directly within a web portal that contains a graphical user interface (GUI) or through external tools that perform cloud‐based computations. Within the database GUI, the median horizontal‐component mHVSR can be plotted against frequency, with the mean and mean ± one standard deviation (representing variability across time windows) provided. Using external interactive tools (provided as a Jupyter Notebook and an R script), users can replot mHVSR (as in the database) or create polar plots. These tools can also derive parameters of potential interest for modeling purposes, including a binary variable indicating whether an mHVSR plot contains peaks, as well as the fitted properties of those peaks (frequencies, amplitudes, and widths). Metadata are also accessible, which includes site location, details about the instruments used to make the measurements, and data processing information related to windowing, antitrigger routines, and filtering.

Seismological Research Letters↗

USGS2021

Horizontal-to-vertical spectral ratios from California sites: Open-source database and data interpretation to establish site parameters

Frequency-dependent horizontal-to-vertical spectral ratios (HVSR) of Fourier amplitudes from three-component recordings can provide information on one or more site resonant frequencies and relative levels of amplification at those frequencies. Such information is potentially useful for predicting site amplification but is not present in site databases that have been developed over the last 15–20 years for the Next-Generation Attenuation (NGA) projects, which instead use the time-averaged shear-wave velocity (VS) in the upper 30 m of the site (VS30) as the primary site parameter and are supplemented with basin depth terms where available. As a consequence, HVSR parameters are also not used in NGA ground motion models. In order for HVSR-based parameters to be used in future versions of site databases, a publicly accessible repository of this information is needed. We adapt a relational database developed to archive and disseminate VS data to also include HVSR. The database provides relevant microtremor-based HVSR data (mHVSR) and supporting metadata. We consider the most relevant data to be the frequency-dependent mHVSR, where the horizontal is taken as the median component and also as a function of horizontal azimuth (referred to as polar plots). Relevant metadata includes site location information, details about the equipment used to make the measurements, and processing details related to windowing, anti-trigger routines, and filtering. We describe the database schema developed to organize and present this information.

California↗

USGS2019

Seismological, geological, and geotechnical engineering aspects of the 2018 MW 6.6 Hokkaido Eastern Iburi earthquake

The 2018 Hokkaido Eastern Iburi MW6.6 earthquake struck the southern coast of the north island of Japan in the early morning (3:08 AM JST) on September 6, 2018. The event had a hypocentral depth of 35 km, centered beneath the port city of Tomakomai. Extremely strong shaking with peak ground acceleration in excess of 0.5 g was felt in the communities directly north of Tomakomai, in the districts of Abira and Atsuma. There, a very high density of landslides occurred in pumices soil that affected the majority of slopes in the region above the floodplain. These landslides were typically a thin veneer of 1 to 3 m of recent (<9000 ybp) volcanic pumice mantling older Kawabata marine sedimentary rocks. The source of the pumice layers are recent eruptions from Mt. Tarumae, south of Shikotsu-ko Caldera lake. Several block megaslides were observed in the Kawabata marine unit. A flow failure resulting from soil collapse or liquefaction was observed in fill deposits placed in a residential community district of Kiyota ward in Sapporo. The community, Satozuka-1 is situated on a natural steep ravine that was filled with pumice soil to level construction area to a gently sloping landscape for housing construction. The flow failure consisted of lateral migration of soil from the upper slope regions of the community onto the surface of the lower community. The upper community topographically deflated as large quantities of fluidized soil flooded the lower streets.

Hokkaido↗

USGS2019

Preliminary report on engineering and geological effects of the July 2019 Ridgecrest earthquake sequence

The Ridgecrest Earthquake sequence included a foreshock event on July 4 2019 (M6.4) and a M7.1 mainshock event on July 5 2019. These events occurred in the Eastern California Shear Zone, near Indian Wells Valley, south of China Lake and west of Searles Valley. GEER has partnered with several organizations to collect perishable data and document the important impacts of these events, including the US Geological Survey, the California Geological Survey, the US Navy, the Southern California Earthquake Center, and local utilities. Critical geotechnical features of this event are extensive left-lateral (M6.4 event) and right-lateral (M7.1 event) surface ruptures over fault segments of variable complexity and width as well as across extensional and compressive step-over zones. We also document lifeline performance at fault crossings (gas, water, electrical), mainshock slip and afterslip, liquefaction and lateral spreading features, and liquefaction effects on structures. These effects are documented using field (ground) mapping and aerial imagery that will support subsequent development of high-resolution digital elevation models. Over 750 ground motions were recorded from the foreshock and mainshock alone, with many additional aftershock records. The data demonstrate significant impacts of site response and rupture directivity on ground motion attributes.

Report↗