2012 First Quarter
- The CENA database is going through an independent QA review. This involves adding comments on the quality of time series in the flatfile. The effort is led by Christine Goulet in collaboration with Chris Cramer and his team. Albert Kottke has started a systematic review of the processed data and Dave Boore independently processed selected earthquake records for comparison with Chris’ results.
Reference rock and site amplification models (Task B)
- The Geotechnical WG is very active with many tasks underway and meetings every month. They are finalizing the epistemic uncertainty assessment plan for their proposed reference rock. Progress is also made on the site databases using various methods to estimate the shear wave velocities at recording stations. Preliminary models for correction to rock conditions are also being developed.
Regionalization (Task C)
- Walter Mooney and his team started a new set of tasks in December 2011 to support the NGA-East Source/Path WG. A major component in the work is to compile an updated catalog of North American crustal structure (both shallow and deep, both P-wave and S-wave velocity and Q) for the CEUS region. The catalog, which contains models from the published literature, is currently being updated to include the most recent data available for both shallow and deep seismic structure.
- Mooney and his team are trying to anticipate the needs of end-users of their data compilation. For this, they have created an Arcmap module for the NRC CEUS hazards project. The Arcmap module allows users to have interactive access to relevant geophysics data. Arcmap allows multiple data layers to be analyzed separately or in sets, and permits the convenient and rapid analysis of our geophysical data. When completed, this effort will allow the user to select data from the index in map-view format and/or data-table format. The map and data tables can be used at either a large or small scale (i.e., regional, state, county). Geo-referenced topographic base-maps allows the user to access attributes such as elevation data and/or rock type and lithology. Major cities, population sizes, interstate highways, state boundaries, and US nuclear power plants may also be plotted.
Regionalization & Source/Path Studies (Tasks C and D)
- Dave Boore published a new paper on stress parameters for nine well-recorded ENA earthquakes. Ref.: Boore, D. M. (2012). Updated determination of stress parameters for several well-recorded earthquakes in Eastern North America, Seismol. Res. Letters 83, 190-199.
- David Boore and Gail Atkinson are working on empirical Green’s functions (eGFs) analysis to estimate the stress parameter from ratios of Fourier acceleration spectra. Their analyses are based on ratios for the mainshock and aftershocks of several ENA earthquakes, including the Mineral, VA, Saguenay, Riviere-du-Loup and Val des Bois earthquakes, from which mainshock stress parameters are estimated. They compare T= 0.1 s and 0.2 s PSA observations with simulations using these derived stress parameters, using a number of proposed geometrical spreading and Q models. Their preliminary finding indicate that a geometrical spreading steeper than 1/R1.3 in the first 60 or 70 km is required to provide stress parameters that are consistent for both methods (eGF analysis and direct inversion of short period PSA). This fast decay of motions is inconsistent with the PSA observations for longer periods (1 or 2 s), thus suggesting the need for a frequency-dependent geometrical spreading. Dave Boore has revised his stochastic-method programs (SMSIM) to handle a new frequency dependent geometric spreading model.
- Jack Boatwright is making progress on the preliminary work he presented at the NGA-East SSHAC workshop in October and at AGU in December. He has finalized the regional spectral analysis of the August 23, 2011, M5.8 earthquake in Mineral, Virginia, and the regional spectral analysis of 14 additional 3.1 ≤ M ≤ 5.0 earthquakes in Canada and New England. The analysis was updated to include the Lake Anna Nuclear Power Station records, which were obtained in January. The addition of this record had a minor effect on the conclusions. The attenuation in the Mid-Atlantic region obtained from the 23 regional accelerographs and broadband recordings of the Mineral earthquake is Q = 466 f 0.48, is very similar to the average attenuation obtained previously for the northeastern part of the Appalachian Province by Boatwright and Seekins (2011), that is, Q = 410 f 0.5.
Finite Fault Simulations (Task E)
- The finite fault simulations validation exercise is being rebooted! All the validations will be redone for a set of common velocity structures that are selected to minimize nonlinear site response effects. New rules for defining the near-surface Vs are currently being developed by members of the TI team. The 2011 Mineral, VA earthquake has also been added to the existing 7 scenarios.
- Paul Somerville submitted his report on Magnitude-Area relationships. The TI team comments are being compiled after their initial review.
Inputs to stochastic ground motion simulation models (Task F)
- Dave Boore and Eric Thompson finalized a paper in which they provide an improved equation for computing duration for root-mean-square oscillator response in the random vibration simulations for the stochastic model. This model will be used in NGA-East to simulate some of the ground motions for GMPE development. Ref.: Boore, D. M. and E. M. Thompson (2012). Empirical improvements for estimating earthquake response spectra with random-vibration theory, Bull. Seismol. Soc. Am., In press.
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