WebSims: A Web-based System for Storage

Kim B. Olsen, & Geoffrey P. Ely

Published 2009, SCEC Contribution #1312

Synthetic time histories from large-scale three-dimensional
dynamic rupture or ground-motion simulations generally
constitute large data sets, which typically require hundreds
of megabytes, gigabytes or even terabytes of storage capacity
(see, e.g., Olsen et al. 2008, 2009). For a seismologist analyzing
rupture propagation or an earthquake engineer performing
seismic hazard analysis, accessing large simulation output can
be a tedious and error-prone procedure. For example, manual
extractions of synthetic ground-motion records at a few sites of
interest, or sliprate functions at desired locations on the fault,
are subject to potential misinterpretation of site coordinates,
units, or coordinate system orientation. If ground-motion synthetics or source-time functions are requested for a larger area (for example, to analyze site effects or rupture variability) additional problems may arise, such as bandwidth-related transfer delays, compatibility of storage devices used for dissemination, and time-consuming metadata assembly. Finally, the user may need to reformat the synthetics to apply post-processing steps, such as filtering or graphical display.

To circumvent these problems we have developed a userfriendly
Web application (WebSims) that allows fast plotting,
processing, storage, and dissemination of rupture and ground motion simulations. WebSims allows interactive access to large
multidimensional gridded synthetic data sets. Since there is a
unique time history at each grid point for each scenario, static
storage of plot images for each point would require extraordinary
amounts of disk space. Thus, clearly, plots must be created
dynamically. WebSims uses software that allows on-the-fly
extraction and plotting of synthetic seismograms via a Web

In terms of plotting and filtering features, but via different
software, WebSims builds on a recent Web-based system
used for validation of dynamic rupture simulations (Harris et
al. 2009). However, an important difference from Harris et
al.’s software is that WebSims is designed to manipulate large
amounts of time series from simulations on a regular grid in
a selected geographic area. WebSims also allows the option
to simultaneously analyze the sliprate functions on the fault
as well as the synthetic seismograms from the radiated waves.
This option allows the user to interactively examine the source
description for causes of amplification and other remarkable
features in the ground-motion simulations. Another important
application of WebSims is to facilitate verification of synthetic
seismograms. For example, Bielak et al. (2009) compared
ground velocities at selected sites for three different code bases,
analyzing, among other features, the effects of anelastic attenuation, absorbing boundary effects, and media averaging. In the future, such analyses can be greatly facilitated by the availability of systems such as WebSims, which will eliminate the
tedious manual handling, reformatting, and dissemination of
synthetic time series after a series of simulations that may be
required to understand the effects of various model parameters.

Olsen, K. B., & Ely, G. P. (2009). WebSims: A Web-based System for Storage. Seismological Research Letters, 80, 1002-1007. doi: 10.1785/gssrl.80.6.1002.