Geology topics

Shideh Dashti

Publications and source records attributed to Shideh Dashti.

4 recordsLinked to original sources

USGS2026

Development of liquefaction-targeted design basis in U.S. seismic provisions

Seismic design criteria for new buildings in the United States have historically focused on life safety performance objectives through minimizing the potential for structural collapse. Development of design criteria to meet this performance objective has evolved over time, leading to the current, risk-targeted maximum considered earthquake (MCE R ) design basis. Corresponding MCE R seismic design loads incorporate the full range of probabilistic ground motion hazard information available from U.S. Geological Survey National Seismic Hazard Models, as well as a representation of the uncertainty in structural collapse capacity. Despite these considerable advances in structural design criteria, guidelines for geotechnical hazards such as liquefaction-induced damage, which continue to be based on uniform ground-shaking hazard (i.e., MCE ground motions), are not well-connected with risk-based, collapse prevention performance objectives. This study, undertaken as part of Building Seismic Safety Council efforts to update recommended seismic provisions through the National Earthquake Hazards Reduction Program, presents probabilistic, liquefaction-targeted design objectives and corresponding ground motion parameters, with a focus on improving consistency in first-level screening criteria for liquefaction hazard assessment. This study identifies a potential maximum acceptable annualized probability of liquefaction triggering ( P L,max ) of 2.5% in 50 years, above which liquefaction consequences and potential mitigation measures would be considered. The P L,max -based design basis is calibrated to effective probabilistic liquefaction hazard levels obtained in practice using current MCE peak ground accelerations, and could be implemented via a new liquefaction-targeted maximum considered earthquake (MCE L ) peak ground acceleration ( PGA L ). The proposed PGA L is derived from probabilistic liquefaction hazard curves and includes uncertainties inherent to liquefaction hazard modeling. The potential design effects of the proposed PGA L are demonstrated via comparison with current MCE PGA levels, effects on first-level liquefaction screening analyses, and improvements in the consistency of P L,max levels across the United States, and for a wide range of site conditions.

conterminous United States↗

USGS2022

The over-prediction of seismically induced soil liquefaction during the 2016 Kumamoto, Japan earthquake sequence

Following the M7.0 strike-slip earthquake near Kumamoto, Japan, in April of 2016, most geotechnical engineering experts believed that there would be significant soil liquefaction and liquefaction-induced infrastructure damage observed in the densely populated city of Kumamoto during the post-event engineering reconnaissance. This belief was driven by several factors including the young geologic environment, alluvially deposited soils, a predominance of loose sandy soils documented in publicly available boring logs throughout the region, and the high intensity ground motions observed from the earthquake. To the surprise of many of the researchers, soil liquefaction occurred both less frequently and less severely than expected. This paper summarizes findings from our field, laboratory, and simplified analytical studies common to engineering practice to assess the lower occurrence of liquefaction. Measured in situ SPT and CPT resistance values were evaluated with current liquefaction triggering procedures. Minimally disturbed samples were subjected to cyclic triaxial testing. Furthermore, an extensive literature review on Kumamoto volcanic soils was performed. Our findings suggest that current liquefaction triggering procedures over-predict liquefaction frequency and effects in alluvially deposited volcanic soils. Volcanic soils were found to possess properties of soil crushability, high fines content, moderate plasticity, and unanticipated organic constituents. Cyclic triaxial tests confirm the high liquefaction resistance of these soils. Moving forward, geotechnical engineers should holistically consider the soil’s mineralogy and geology before relying solely on simplified liquefaction triggering procedures when evaluating volcanic soils for liquefaction.

Mount Aso↗

USGS2017

Geotechnical aspects of the 2016 MW 6.2, MW 6.0, and MW 7.0 Kumamoto earthquakes

The 2016 Kumamoto earthquakes are a series of events that began with an earthquake of moment magnitude 6.2 on the Hinagu Fault on April 14, 2016, followed by another foreshock of moment magnitude 6.0 on the Hinagu Fault on April 15, 2016, and a larger moment magnitude 7.0 event on the Futagawa Fault on April 16, 2016 beneath Kumamoto City, Kumamoto Prefecture on Kyushu, Japan. These events are the strongest earthquakes recorded in Kyushu during the modern instrumental era. The earthquakes resulted in substantial damage to infrastructure, buildings, cultural heritage of Kumamoto Castle, roads and highways, slopes, and river embankments due to earthquake-induced landsliding and debris flows. Surface fault rupture produced offset and damage to roads, buildings, river levees, and an agricultural dam. Surprisingly, given the extremely intense earthquake motions, liquefaction occurred only in a few districts of Kumamoto City and in the port areas indicating that the volcanic soils were less susceptible to liquefying than expected given the intensity of earthquake shaking, a significant finding from this event.

Report↗

USGS2016

An overview of the geotechnical damage brought by the 2016 Kumamoto Earthquake, Japan

The 2016 Kumamoto earthquake with a moment magnitude of 7.0 (Japanese intensity = 7) that struck on April 16 brought devastation in many areas of Kumamoto Prefecture and partly in Oita Prefecture in Kyushu Region, Japan. The earthquake succeeds a foreshock of magnitude 6.5 (Japanese intensity = 7) on April 14. The authors conducted two surveys on the devastated areas: one during April 16-17, and the other during May 11-14. This report summarizes the damage brought to geotechnical structures by the two consecutive earthquakes within a span of twenty-eight hours. This report highlights some of the observed damage and identifies reasons for such damage. The geotechnical challenges towards mitigation of losses from such earthquakes are also suggested.

Report↗