Homework 1 (pdf) - Geotechnical Earthquake Engineering

CE 275: Geotechnical Earthquake Engineering
Prof. R. B. Seed
Fall Semester, 2006
Assignment 1
Part I:
In this section, you will be encouraged to surf the net a bit and familiarize yourself with
the seismicity of the world in which we live. Begin by accessing the USGS seismic hazards web
site at http://earthquake.usgs.gov/ .
1. Hunt around on this parent USGS website and find “Current Earthquake Info.” What is the
current time and date? Among the last 20 or so earthquakes logged (world-wide), where was
the largest and what was its magnitude?
2. Access the U.S. national map for seismic shaking hazard (for “Firm Rock” site conditions) at
http://earthquake.usgs.gov/regional/. This is a mapping of probabilistic seismicity for the
country (and parts of the world) based on the assumption that the entire country has surface
site conditions corresponding to what the USGS calls “firm rock” (defined as having a shear
wave velocity of V s = 760 m/sec over the top 30 m.) This corresponds to the “soft to medium
rock” conditions of the NEHRP site class B/C boundary.
Near the top of the page, click on National Seismic Hazard maps, then on the next page
under National Seismic Hazard maps, click on Coterminous U.S. From there, use the 2002
Custom Mapping for spectral values, and the 1996 deagregation (as the 2002 deaggregation
has “difficulties”.)
(a) Find Topeka, Kansas. For Topeka, find the peak horizontal acceleration with a 10%
probability of exceedance in 50 years (~ 475 year return interval). Also find the
corresponding spectral accelerations for periods of 0.2, 0.3, and 1.0 seconds. (You may
need to enter Latitude and Longitude coordinates to get these spectral values; the
interactive map has limitations. The map to use is at the bottom of the page and is called
Interactive Hazard Maps; US 2002. When you press the access button, the website says
that you have now reached the 1996 interactive map, but that’s a typo; it is the 2002
map.) Plot the Equal Hazard Spectrum (5% damped, elastic). At periods of greater than
1.0 seconds, assume that the spectral ordinates reduce at a rate proportional to 1/T (where
T = Period in seconds). Now, on the same plot, repeat the exercise, but for 2%
probability of exceedance in 50 years, [or roughly the 2,500 year return interval level].
Kansas might not be too bad a place to live? (Too boring?)
(b) Repeat (a) above, but this time for the University of Texas at Austin. Does Texas face
much seismic risk?
(c) Considering only the 10% probability of exceedance in 50 years level, draft Equal Hazard
Spectra (5% damped, Elastic) for the center of the New Madrid seismic region, and also

for the city of Charleston (in the Charleston seismic region). These are the two principal
“eastern U.S.” seismic zones. Plot both spectra on the same plot.
(d) Now consider Charleston a bit more closely. Plot approximate Equal Hazard Spectra for
Charleston for both the 10% probability of exceedance in 50 years (~475 year return
interval) level, and the 2% probability of exceedance in 50 years (~2,500 year return
interval) level [Plot these both on the same figure.] Using the 1996 “deaggregation”
option, deaggregate these spectra by Magnitude (M) and Distance (R). Note that the
deaggregation will be different at shorter and longer periods, so you will want to
deaggregate for PGA and for the various spectral ordinates separately.
• Using your Equal Hazard Spectrum for 10% in 50 years, and the
deaggregation, recommend the approximate initial characteristics (a max , M w
and R) for a “design basis” earthquake for use in design of an 2 to 3-story
apartment complex and shopping center in Charleston.
• Using your Equal Hazard Spectrum for 2% in 50 years, and the deaggregation,
recommend the approximate initial characteristics characteristics (a max, M w
and R) for a “design basis” earthquake for use in design of a major earth dam
(with a crest height of approximately 350 feet, and a predominant period of
about 0.8 seconds) near Charleston.
Part II:
3. Find the location where you live (while attending U. C. Berkeley.) Again, find the PGA, and
the S A values for T = 0.2, 0.3 0.5 and 1.0 seconds, and plot the Equal Hazard Spectrum (5%
damped, elastic) for a probability of exceedance of 10% in 50 years (the presumed UBC
building code level.) On the same figure, plot the actual response spectrum from the current
UBC for Site Class C conditions. (Don’t forget to apply the near field factors if appropriate.)
Does this worry you? Remember, if your building is more then about ten years old, it was
probably designed for even lesser levels of shaking.
Part III:
Now, on your own volition, and despite a rigorous schedule of competing priorities and
conflicting assignments from other courses, access another web site (still under construction)
sponsored by CDMG at http://www.consrv.ca.gov/cgs/, and explore a bit. This site is dedicated
more locally to California, and presents similar information to that presented by the USGS site,
but it is not yet as well along.
4. Repeat the First part of Question #3 above. Is the strong shaking hazard mapping of this site
the same (same basis, and same values) as the USGS site? (Don’t spend a long time on this
one….just make a few quick checks.)