The October federal government shutdown affected some tasks directly funded by the NRC to the USGS. Overall, the project team was still able to make substantial progress.
- NGA-East related presentations at the SSA Eastern Section Annual Meeting, Charlevoix, Quebec, Canada, October 6-8 (see program for abstracts.)
- “The NGA-East Database: Development, Challenges and Products”, Goulet, Christine A.; Kishida, Tadahiro; Cramer, Chris H.; Darragh, Robert B.; Silva, Walter J.
- “Validation of Ground Motion Simulation Methods for the NGA-East Project”, Goulet, Christine A.; The BroadBand Platform Validation Team
- “The Attenuation of Fourier Amplitudes for Rock Sites in Eastern North America”, Atkinson, Gail M; Boore, David M.
- “Comparison of NGA-West2 Ground Motion Prediction Equation with Recently Recorded Data in Eastern North America”, Hassani, Behzad; Atkinson, Gail M.
- Due to the federal government shutdown, Dr. Boatwright (USGS) was unable to present his most recent findings on ENA events’ analyses at the conference.
Data Sets (Task A)
- After a first round of QA of the re-processed records, the NGA-East decision was to extend the Coda time-window part of the records. This change will not affect spectral values computed from the records; however, the longer and uniformly processed records are expected to have a wider range of applications with this change.
- A PEER report documenting the ground motion data collection and processing is under preparation with specific chapters assigned to the various contributors to the NGA-East Database. The content of the draft report will be reviewed and discussed by the TI team during a Working Meeting at the end of January 2014.
- Drs. Boore (USGS) and Goulet (PEER) submitted a paper entitle “The Effect of Sampling Rate and Anti-aliasing Filters on High-Frequency Response Spectra”. This paper documents a process to assess the usable bandwidth of recorded ground motions. This is especially important for the NGA-East database since more than 70% of the records come from the low-sampling rate of the TA array. It is important to know the range of periods for which the spectral response is adequately captured by these records. After a round of reviews, the paper was accepted for publication in the Bulletin of Earthquake Engineering.
- One important factor affecting high frequency ground motions in CENA is Kappa. In point source stochastic models based on a Brune spectral shape for Fourier amplitudes, Kappa controls the rate of decay of high frequencies. . The investigation of Kappa for CENA was not formally included in the NGA-East project plan. We are now including its assessment as part of a database parameter. A series of meetings were held on this issue, involving various NGA-East participants (TI team, Database, Geotech and Path Working Groups), Drs. Ktenidou (PEER visiting scholar) and Kishida (PEER post-doctoral research fellow), and Drs. Silva and Darragh (Pacific Engineering and Analysis).
- Dr. Ktenidou is refining a new screening approach for selecting records based on their potential for Kappa computation. The innovative method considers magnitude, Vs30, frequency bandwidth of records. The method will be applied to the final database flatfile for the selection of methods.
Reference rock and site amplification models (Task B)
- The Geotechnical Working Group (GWG) continues to be very active with their tasks and have monthly meetings attended by the TI Leads Drs. Goulet and Abrahamson.
- The final report on reference rock condition has been submitted to PEER for publication.
- The group continued their development of protocols of the large-scale site response simulations that will be conducted using input ground motions and typical soil profiles. The analysis will include approximately 2 million site response simulations. The output of these simulations will be used for development of nonlinear site amplification functions or models.
- The group worked very closely with the TI Leads to provide preliminary answers on the impact of soil non-linearity on Fourier Amplitude Spectra Vs. Response Spectra. The work essentially consisted of running a subset of their ground response simulations (from above) and to present summary results to the TI Leads. This exercise was very useful to the NGA-East team and helped the development of new metrics for the assessments of site effects in both spectral spaces
- Dr. Boore (USGS) and Dr. Goulet (PEER) worked on the verification and updating of site factors to interpolate ENA response spectral values from a BC site condition to a site with Vs30=1000 m/s. This extrapolation used ratios of the BC and very hard rock ratios from the Atkinson and Boore (2006) GMPEs, as discussed in Ratios of GMIMs for very hard rock (vhr) and BC conditions for the Atkinson and Boore (2006) ENA GMPEs, as modified in Atkinson and Boore (2011). This work supplemented the Reference rock correction memo developed by the Geotech Working Group in October 2012.
- The TI leads (Drs. Goulet and Abrahamson) continued with regular meetings with the regionalization team. This small group is composed of two complementary teams (Dr. Mooney, Ms. Dreiling and Mr. Isken from the USGS) and Drs. Chapman (Virginia Tech.) and Pezeshk (U. Memphis) and their students.
- The group finalized the statistical evaluation of ground motion simulations ran to assess the impact of different crustal regions on ground motion spectral amplitudes.
- A summary of the process, methodology and results from the USGS team was compiled into a draft report to be finalized in early 2014.
- Dr. Chapman and his team started running parallel simulations considering the frequency-dependence of attenuation (Q). Both sets of simulations are expected to provide complementary information on the regionalization of path effects.
- Results of work from both teams are to be presented at the Working Meeting in January 2014 where the TI team is expected to provide further recommendations on the work and documentation requirements.
- Dr. Boatwright (USGS) compiled and analyzed records from various events to further inform the regionalization of source parameters. Following a collegial request for average stress parameter in ENA, Boatwright re-evaluated stress parameters for the complete set of NENA earthquakes that have been analyzed, some 63 events reaching back to 1986. This effort makes clear that the earthquakes in the Charlevoix and Lower St Lawrence have the highest stress parameters and the clearest dependence of stress parameter on depth. The earthquakes in New England, New York, and the Western Quebec Seismic Zone have lower stress parameter values. For this set of earthquakes, there is some dependence of the stress parameter value on magnitude. The estimation of stress parameter is important in the selection of records for Kappa analyses. These results are to be presented to the TI team at the regionalization working meeting.
- The collaborative simulations group (PEER, SWUS and SCEC) kept very active in the last few months and continued to have their weekly phone calls.
- The CENA earthquake scenarios have been defined for validation purposes. The three main events considered at Saguenay, Riviere-du-Loup and Mineral.
- As part of the validation team effort, Dr. Anderson (U. Nevada, Reno) contributed by carefully crafting velocity profiles for the Quebec and Virginia events. The final profiles were based on sets of regional crustal profiles provided by Dr. Mooney and his team. The simplified 1D profiles were accepted by the validation team and used to generate the Green’s function for deterministic methods.
- The beginning of the validation for those events triggered further adjustments for Dr. Olsen’s (SDSU) simulation method, which was never calibrated for small magnitude events.
- Dr. Graves (USGS) started iterating in the parameter space to be able to capture a good fit for Saguenay and the two events with the Graves and Pitarka methodology.
- Dr. Assatourians (U. Western Ontario) started the calibration for EXSIM. The validation of methods for the Saguenay event has been a challenge for many years and this validation exercises is now facing the difficulty.
- Drs. Atkinson and Mr. Yenier (U. Western Ontario) have submitted a paper summarizing their findings on appropriate definition of point-source stochastic parameters for ENA events.
- Dr. Atkinson and Mr. Hassani (U. Western Ontario) also have a paper in preparation on use of referenced empirical method to understand differences between NGA-E database and WNA GMPEs, to shed further light on constraints on point-source (and finite-fault) parameters for ENA. A summary of findings was also shared at SSA-East (see above)
- Dr. Frankel (USGS) has been investigating the effects of rupture directivity and focal mechanism on the amplitude decay with distance of synthetic seismograms made for the Riviere-du-Loup earthquake and the Mn4.1 earthquake of June 13, 2003 near Charlevoix. The synthetics were made with deterministic Green’s functions using a reflectivity code. The choice of rupture plane and hypocenter significantly affect the distance decay of the 1 Hz Fourier spectral amplitude of the synthetic acceleration waveforms. Frankel continues to work on making broadband synthetics for M5.5-7.5 earthquakes for ENA and assessing the factors that control the spectral accelerations as a function of distance and magnitude.
Atkinson, G.M. and D.M. Boore (2006). Earthquake ground-motion prediction equations for eastern North America, Bull. Seismol. Soc. Am. 96, 2181—2205.