Capturing a seismic wave field: Animation of kinematic GPS data recorded during
the 2011 Tohoku-oki Earthquake, Japan.
Ronni Grapenthin and Jeffrey T. Freymueller
Geophysical Institute, University of Alaska Fairbanks, USA
Earthquakes displace the ground during rupture and
create seismic waves, which involve dynamic displacements that travel around the globe. Only recently did we measure dynamic displacements directly
with high-rate Global Positioning System (GPS) data1
rather than using inferred displacements from seismic
records. However, due to sparse station coverage,
such data are traditionally presented as time series
of a few GPS stations neglecting spatial correlation
in the signal presentation. We visualize directly measured dynamic and permanent displacements caused
by the March 11, 2011, Mw 9.0 Tohoku-oki earthquake2
as a vector field based on data recorded by the dense
Japanese GPS Earth Observation System (GEONET)3
(Fig. 1, 2, Animation). The animation captures dynamic
ground motion due to S-waves (body waves), Love
waves and Rayleigh waves (surface waves, Fig. 3). Our
animation also shows the growth of the earthquake
rupture over time (Fig. 1) and illustrates differences of
earthquake magnitude using two smaller aftershocks
(Fig. 4). The displacements in map view are easily understandable by specialists and non-specialists alike.
Real time availability of such displacements could be
of great use in earthquake early warning4.
1. Observations
1.1 Permanent and Dynamic Displacements
2. Methods
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Geospatial Information Authority (GSI) of Japan
provided original RINEX files for available GEONET
sites to Caltech.
Team ARIA (JPL/Caltech) used the GIPSY software
(JPL) to compute three-dimensional 30 s kinematic
position estimates5 for these sites.
Access to ARIA solutions is provided by the
Tohoku-oki Supersite6.
We filtered ARIA solutions for noise reduction and
eliminated a few noisy stations entirely.
Software used to create movies: Generic Mapping
Tools7, ImageMagick, mencoder, ffmpeg (freely
available under the GNU General Public License).
Figure 2: (A) Permanent displacements after the Mw 9.0 earthquake: blue is horizontal, red is vertical. Vertical displacements are almost all subsidence, which means that
all slip-induced uplift occurred off-shore. These displacements are subtracted from panels (B) and (C) to isolate the propagating seismic waves. (B,C) Vertical displacements
(black: uplift, gray: subsidence) and horizontal displacements from 187-367 s after rupture initiation (rupture took about 180 s). ‘S’, ‘L’, and ‘R’ indicate S-wave, Love wave,
and Rayleigh wave, respectively. Box in (C) indicates the location for Figure 2.
1.2 Wave Pattern
1.3 Orders of Magnitude
Figure 3: Observed wave patterns as they propagate through the box in Fig. 1C; times are relative to
origin time. Early records are green, later ones are black. (A) S-wave. (B) Love wave; note the welldefined displacements perpendicular to the propagation direction. The trailing smaller black arrows
indicate the following Rayleigh wave (see Fig. 3). (C) Rayleigh wave.
Figure 4: Permanent horizontal displacements of the earthquakes.
(A) Mw 9.0 (B) Mw 7.9 and Mb 6.4 (8, displacement in (A) subtracted).
3. Results and Conclusions
We capture:
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three events2,8: Mw 9.0, 05:46:23 UTC; Mb 6.4,
06:09:30 UTC; Mw 7.9, 06:15:40 UTC.
propagation of S-wave, Love wave, Rayleigh wave.
the main rupture in 6 frames (180 s); grows to south.
We find:
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Figure 1: Evolution of permanent displacements due to the
Mw 9.0 rupture. Times are given relative to rupture initiation
time. Blue is horizontal, red is vertical. Dynamic features
emerge in lower three panels.
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surface displacement on land begins between 37 s
and 67 s after rupture initiation2, expected S-wave
delay is about 15-20 s.
vector fields in map view increase the understanding
of earthquake mechanics.
earthquakes of different magnitudes in one animation
visualize the meaning of earthquake size.
real time availability of these data in self-organizing
ad-hoc networks9 will be of great use in earthquake
early warning, and tsunami warning.
generalization of our code will allow for creation /
analysis of such visualizations in near real time.
References
Animations
If I am not around to show them check here:
http://www.gps.alaska.edu/ronni/sendai2011.html
1. Larson, K.M., Bodin, P., Gomberg, J., Using 1-Hz GPS Data to Measure Deformations Caused by the Denali Fault Earthquake, Science,
300, 1421-1424 (2003).
2. USGS, http://earthquake.usgs.gov/earthquakes.
3. Sagiya,T., A decade of GEONET: 1994-2003 –The continuous GPS observation in Japan and its impact on earthquake studies–, Earth
Planets Space, 56, xxix-xli, (2005).
4. Crowell, B.W., Bock, Y., Squibb, M.B., Demonstration of Earthquake Early Warning Using Total displacement Waveforms from Real-time
GPS Networks, Seis. Res. Lett., 80, 5, 772-782 (2009).
5. Simons, M. et al., The 2011 Magnitude 9.0 Tohoku-Oki Earthquake: Mosaicking The Megathrust From Seconds To Centuries, Science,
submitted (2011).
6. GEO Supersites, http://supersites.earthobservations.org/sendai.php.
7. Wessel, P., Smith, W. H. F., New, improved version of Generic Mapping Tools released, EOS Trans. Amer. Geophys. U., 79, 47, 579, (1998).
8. USGS aftershock map, http://earthquake.usgs.gov/earthquakes/seqs/events/usc0001xgp.
9. Fleming, K., et al., The Self-organizing Seismic Early Warning Information Network (SOSEWIN), Seismological Research Letters, 80, 5,
755-771 (2009).
We thank C. Tape, D. Christensen, and A. Arendt for discussion; P. Haeussler, and B. Atwater provided helpful comments on early versions of the animations. We used A. Aschwanden’s LATEX template as a basis for this poster.