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Sanaz Rezaeian: PEER-USGS Collaboration on Modeling Earthquake Ground Motions and Seismic Hazard Analysis


Project Title: PEER-USGS Collaboration on Modeling Earthquake Ground Motions and Seismic Hazard Analysis
Mendenhall Fellow: Sanaz Rezaeian, (303) 273-8565, srezaeian@usgs.gov; sanazr128@yahoo.com
Duty Station: Berkeley, CA (March–July 2011) ; Golden, CO (July 2011–March 2013)
Start Date: March 14, 2011
Education: Ph.D. (Structural Engineering), University of California, Berkeley, 2010
Research Advisor: Mark Petersen, (303) 273-8546, mpetersen@usgs.gov; Nicolas Luco, (303) 273-8683, nluco@usgs.gov
  Sanaz Rezaeian

Project Description: The national seismic hazard maps, which are used in building codes, are of great importance in seismic design and analysis of structures. These maps are periodically updated by the U.S. Geological Survey (USGS) to incorporate the results of new research. The times of these updates coincide with the schedule for updates of building codes. The last update was in 2008; the next one is tentatively scheduled for 2014. In development of seismic hazard maps, models that estimate the severity of ground shaking for a potential earthquake are required. These models, often referred to as Ground Motion Prediction Equations (GMPEs), are used to estimate both the median and uncertainty of the intensity of ground shaking. The latest GMPEs for the Western United States were developed in the Next Generation Attenuation (NGA) project and were incorporated in the 2008 seismic hazard maps. In 2010, the Pacific Earthquake Engineering Research (PEER) Center started two new projects to improve and update the NGA models for the Western United States (NGA-West2) and to develop NGA models for the Central Eastern United States (NGA-East). The results are to be implemented in upcoming revisions of the national seismic hazard maps.

The current project is a collaborative effort between PEER and USGS. The specific tasks have been designed to fulfill the requirements of the NGA-West2 and NGA-East proposals and to update the national seismic hazard maps accordingly. A brief description of each task is provided below.

Task 1: Scaling of NGA Models for Damping Ratios Other Than 5 Percent (NGA-West2 Topic 6)

The current NGA models for elastic response spectra are for 5-percent viscous damping. In reality, structures can have different damping ratios depending on the structural type. The current guidelines to translate the 5-percent damped elastic response spectra to other damping values are outdated. We will develop a new model for the Damping Scaling Factor (DSF) that can be used to adjust the 5-percent damped spectral ordinates predicted by the NGA models to other damping values. A range of damping ratios from 0.5 percent to 30 percent is of interest. Implementation of DSF in the seismic hazard maps could be of great importance to structural engineers and loss modelers because it will allow them to use a damping value that better correlates with response of the specific structures under consideration. To make the final decision on this implementation, sensitivity studies are required to investigate the effects of different damping ratios on hazard estimation.

A database of over 8,000 records will be used in modeling DSF. Using these records, figure 1 shows that ln(DSF) follows a normal distribution, while figure 2 reveals a systematic pattern between DSF and spectral period. Such information will be used in the modeling process.


Figure 1   Figure 2
Figure 1 Figure 2

Task 2: Vertical Ground Motion Modeling (NGA-West2 Topic 3, and NGA-East)


The current NGA models are for the geometric mean of two horizontal ground motion components. We will develop GMPEs for the vertical ground motion. A separate group from PEER will be modeling the site amplification factors that are specific to vertical motion. These factors account for the site effects due to nonlinear soil behavior and basin effects. We will work with this group and implement their results to arrive at the final model.

Task 3: Modeling Epistemic Uncertainty (NGA-West2 Topic 7)

Modeling the epistemic (“model to model”) uncertainty is an important element in probabilistic seismic hazard analysis (PSHA). A consensus epistemic uncertainty model will be developed for NGA.

Task 4: Implementation in the National Seismic Hazard Maps

In addition to those described above, the NGA-West2 and NGA-East projects cover many other topics, some of which are listed in the table below. It is clear that the results of some topics must be implemented in the next revision of the seismic hazard maps (for example, NGA-West2 Topics 3, 4 and 5). For other topics (for example, NGA-West2 topic 6), we will conduct sensitivity studies to decide on the necessity of implementation.



NGA-West2 Topics


1

Directivity Models for NGA Relations

2

Directionality of Ground Motions

3

Models for Vertical Ground Motion

4

Verification of NGA Models for Low Magnitude Earthquakes in California

5

Verification of NGA Models for Recent Moderate and Large Magnitude Earthquakes Worldwide

6

Scaling of NGA Models for Damping

7

Developing a Consensus Epistemic Uncertainty Model for NGA

8 Further Development of Site Response in NGA Models



References

2008 United States National Seismic Hazard Maps: http://earthquake.usgs.gov/hazards/products/conterminous/2008/
Next Generation Attenuation Relationships for Western US (NGA West): http://peer.berkeley.edu/ngawest/
Enhancement of Next Generation Attenuation Relationships for Western US (NGA-West 2): http://peer.berkeley.edu/ngawest2/
Next Generation Attenuation Relationships for Central & Eastern North-America (NGA-East): http://peer.berkeley.edu/ngaeast/



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Last modified: 16:08:32 Thu 13 Dec 2012