Progress Report, Kim Olsen, SDSU, Geoinformatics EAR-1349180, June 2015.
1) Research accomplishments, Year 1
We have continued to evaluate the SCEC CVMs in terms of accuracy of ground
motion prediction for seismic hazard analysis. Specifically, we have carried out an extensive
study of the role of small-scale crustal heterogeneities on the variation of the ground motion
intensities. The small-scale heterogeneities have been parameterized as Von Karman
distributions, and we have estimated the parameters of the distributions by variogram
inversion in best agreement with selected sonic logs and Vs30 measurements in the Los
Angeles basin. We estimate Hurst numbers of 0.0-0.1, vertical correlation lengths of 50150m, and standard deviations of ~5%. Von Karman distributions based on these
parameters were then added to the SCEC CVM-S, and we estimated the ensemble ground
motion intensities for a suite of random seed numbers for the 2008 Mw 5.4 Chino Hills
event. We find that the small-scale heterogeneities can amplify or de-amplify ground
motions for 0-2.5 Hz waves by up to a factor of two. A relation between the quality factor
(Qs) and Vs of Qs/Vs~100-150 (Vs in km/s) provides the largest goodness-of-fit (GOF) values
and best-fitting peak motion attenuation with distance when accounting for a scattering
medium for the Chino Hills earthquake. These Qs/Vs relations are less attenuating than that
routinely used for the LA basin in the past, when smoother CVMs have been used (no smallscale heterogeneities included), suggesting a trade-off between Q and the strength of the
small-scale variation.
In collaboration with Lozos, Oglesby, Brune and Brune (Lozos et al., 2015) we
simulated dynamic rupture and broadband ground motions for a geometrically-complex
model of the San Jacinto fault (SJF) with a 25 km long extensional stepover with an average
of 4 km separation. We used the 3D CVM-S for the rupture and low-frequency simulations,
and the broadband method by Olsen and Takedatsu (2015) to add the higher frequencies.
The main stepover serves as a primary barrier to rupture in our model, producing event
sizes (Mw5.4-6.9) that are consistent with the historical behavior of the SJF. The largest
broadband synthetics are a good match to the leading ground-motion prediction equations
and are generally consistent with the distribution of nearby-located Precariously Balanced
Rocks (PBRs). Thus, the PBRs confirm that our models produce realistic rupture extent and
shaking, and the simulations provide a validation of the CVM-S in the area around the SJF.
However, the maximum event size for the San Jacinto fault predicted by the Uniform
California Earthquake Rupture Forecast Version 3 (UCERF3, Field et al., 2013; implicating
an M7.4-8.3 rupture, on average, every 200 years) would likely be inconsistent with the
presence of the PBRs near the SJF.
Impact on principal discipline: The scattering from small-scale heterogeneities and
associated trade-off with intrinsic Q can have important effects on the seismic hazard, in
particular at higher frequencies, and should be included in future numerical models. PBRs
confirm that shaking levels produced by the 3D CVMs are realistic, but suggests that the
maximum event size in UCERF3 for the SJF is too large.
2) Broader impacts:
We have provided code to include statistical models of the small-scale heterogeneities into
the SCEC UCVM software, which is documented and available to all interested modelers. The
validation through the PBRs has provided confidence in the CVMs near the SJF for future
hazard modeling.
3) Journal papers:
Lozos, J., K.B. Olsen, J. Brune, R. Takedatsu, R. Brune, and D.D. Oglesby (2015). Broadband
ground motions from dynamic models of rupture on the northern San Jacinto fault, and
comparison with precariously balanced rocks, Bull, Seis. Soc. Am., Vol 105. (August issue,
in press), doi: 10.1785/0120140328.
Shaw, J.H., A. Plesch, C. Tape, M. peter Suess, T.H. Jordan, G. Ely, E. Hauksson, J. Tromp, T.
Tanimoto, R. Graves, K. Olsen, C. Nicholson, P.J. Maechling, C. Rivero, P. Lovely, C.M.
Brankman, J. Munster (2015). Unified structural representation of the southern California
crust and upper mantle, Earth and Planetary Science Letters 415, 1-15.
4) Abstracts:
Lozos, J., K.B. Olsen, J. Brune, R. Takedatsu, R. Brune, and D.D. Oglesby. Broadband ground
motions from dynamic models of rupture on the northern San Jacinto fault, and comparison
with precariously balanced rocks, Seismological Society of America Annual Meeting,
Pasadena, Poster #45, Tuesday April 21, 2015.
Savran, W. and K.B. Olsen. Analysis of 3D deterministic broadband (0-25 Hz) ground
motions generated by models of small-scale crustal heterogeneities and Q(f), Seismological
Society of America Annual Meeting, Pasadena, Poster #22, Tuesday April 22, 2015.
Gill, D., P. Small, R. Taborda, E. Lee, K.B. Olsen, P. Maechling, T.H. Jordan. Standardized access
to seismic velocity models using the unified community velocity model (UCVM) software.
Seismological Society of America Annual Meeting, Pasadena, Poster #96, Tuesday April 22,
2015.
Savran, W., K.B. Olsen, and B.H. Jacobsen (2014). Unique amplification patterns generated
by models of small-scale crustal heterogeneities, AGU Fall Meeting 2014, San Francisco, CA,
Dec 15-19, presentation S41E-06.
Gill, D., P. Small, P. Maechling, T.H. Jordan, J.H. Shaw, A. Plesch, P. Chen, E.J. Lee, R. Taborda,
K.B. Olsen, S. Callaghan. UCVM: Open source software for understanding and delivering 3D
velocity models, AGU Fall Meeting 2014, San Francisco, CA, Dec 15-19, presentation IN23D3752.
Withers, K.B., K.B. Olsen, Z. Shi, and S. Day. High-complexity deterministic Q(f) simulation of
the 1994 Northridge Mw6.7 earthquake, SCEC Annual Meeting, Palm Springs, Sept 2014,
poster # 66.
Savran, W.H., and K.B. Olsen. Validation exercise for two southern California earthquakes.
SCEC Annual Meeting, Palm Springs, Sept 2014, poster # 65.
5) List of staff, post-doc or students supported.
Rumi Takedatsu, Research Assistant (staff), rtakedatsu@mail.sdsu.edu. Broadband ground
motion code development, verification, validation and computation, ground motion maps.
William Savran, PhD student, wsavran@gmail.com. Development of code for generating and
validating statistical models of small-scale heterogeneities. Large-scale computation of
ground motions in CVMs with and with small-scale heterogeneities.
6. List of any countries visited for research on this project N/A
7. Any collaborators you might have in addition to the team here
B.H. Jacobsen, Univ. Aarhus, Denmark.
8. Figure.
Snapshot of 0-2.5 Hz waves propagating in a medium including small-scale heterogeneities
(blue to red colors in fence diagram), parameterized by a Von Karman model with a Hurst
exponent of 0.05, a correlation length of 250 m, a standard deviation of the perturbations
with respect to the background model of 5%, and a horizontal to vertical anisotropy of 5.
The waves are depicted by surfaces of constant particle velocity (isosurfaces, magenta
color). The snapshot helps understand how the waves follow banded propagation paths,
guided through the lower velocity regions (blue) and mostly circumvent concentrations of
higher-velocity material (red) at different scales. A similar wave guide phenomenon, but on
a much larger scale, was found to channel large-amplitude waves from a large earthquake
scenario on the San Andreas fault ("ShakeOut") into the Los Angeles basin through an
interconnected series of low-velocity sedimentary basins.