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Geology topics

Homa Lee

Publications and source records attributed to Homa Lee.

3 recordsLinked to original sources

A geomechanical approach for the genesis of sediment undulations on the Adriatic shelf

This study is among the first to examine the genesis of the seafloor and subsurface undulations on the Adriatic continental shelf by integrating stratigraphic information and in situ and laboratory geotechnical measurements. Interpretation of sediment behavior is based on a 32-m-long borehole crossing (1) a possible shear plane and (2) a silty clay layer at about 20 m below seafloor (mbsf) on which sediment undulations are rooted and could be interpreted as a potential weak layer succession. Our main results in terms of triggering mechanism for the observed undulations show that under an earthquake, liquefaction and/or failure of the silty-clay sediments (weak layer) leading to deformation of the upper more cohesive sediments is possible only when such a layer is buried by less than 5 m. For greater burial thicknesses, this silty clay becomes stable under the confining lithostatic pressure exerted by the overlying sediment. This work shows that the seafloor and subsurface undulations observed in the study area are most probably the result of an early deformation process of the seafloor followed by a depositional process.

Adriatic shelf

Increasing resiliency to natural hazards - A strategic plan for the Multi-Hazards Demonstration Project in Southern California

The U.S. Geological Survey (USGS) is initiating a new project designed to improve resiliency to natural hazards in southern California through the application of science to community decision making and emergency response. The Multi-Hazards Demonstration Project will assist the region’s communities to reduce their risk from natural hazards by directing new and existing research towards the community’s needs, improving monitoring technology, producing innovative products, and improving dissemination of the results. The natural hazards to be investigated in this project include coastal erosion, earthquakes, floods, landslides, tsunamis, and wildfires. Americans are more at risk from natural hazards now than at any other time in our Nation’s history. Southern California, in particular, has one of the Nation’s highest potentials for extreme catastrophic losses due to natural hazards, with estimates of expected losses exceeding $3 billion per year. These losses can only be reduced through the decisions of the southern California community itself. To be effective, these decisions must be guided by the best information about hazards, risk, and the cost-effectiveness of mitigation technologies. The USGS will work with collaborators to set the direction of the research and to create multi-hazard risk frameworks where communities can apply the results of scientific research to their decision-making processes. Partners include state, county, city, and public-lands government agencies, public and private utilities, companies with a significant impact and presence in southern California, academic researchers, the Federal Emergency Management Agency (FEMA), National Oceanic and Atmospheric Administration (NOAA), and local emergency response agencies. Prior to the writing of this strategic plan document, three strategic planning workshops were held in February and March 2006 at the USGS office in Pasadena to explore potential relationships. The goal of these planning sessions was to determine the external organizations’ needs for mitigation efforts before potential natural hazard events, and response efforts during and after the event. On the basis of input from workshop participants, four priority areas were identified for future research to address. They are (1) helping decision makers design planning scenarios, (2) improving upon the mapping of multiple hazards in urban areas, (3) providing real-time information from monitoring networks, and (4) integrating information in a risk and decision-making analysis. Towards this end, short-term and out-year goals have been outlined with the priorities in mind. First-year goals are (1) to engage the user community to establish the structures and processes for communications and interactions, (2) to develop a program to create scenarios of anticipated disasters, beginning in the first year with a scenario of a southern San Andreas earthquake that triggers secondary hazards, (3) to compile existing datasets of geospatial data, and (4) to target research efforts to support more complete and robust products in future years. Both the first-year and out-year goals have been formulated around a working-group structure that builds on existing research strengths within the USGS. The project is intended to demonstrate how developments in methodology and products can lead to improvement in our management of natural hazards in an urban environment for application across the Nation.

Open-File Report

Mapping southern Puget Sound delta fronts after 2001 earthquake

A moment magnitude 6.8 earthquake struck southern Puget Sound (Figure 1) on February 28, 2001, causing an estimated $0.7–$1.4 billion in damages to buildings and roadways in the region [Williams et al., 2001]. The earthquake source was 52 km deep, and the epicenter was located close to the Nisqually River delta in the same location as the epicenter of the magnitude 7.1 earthquake of 1949 (http://www.geophys.washington.edu/seis/pnsn/info_ general/). These deep earthquakes occurred in the eastward-dipping subducting slab of the Juan de Fuca plate and typically caused less damage than shallower, crustal events of the same magnitude. Details of the seismology and effects of the earthquake can be found at http://earthquake.usgs.gov/activity/latest/ eq_01_02_28.html.

Washington