Abstracts
2010 AGU Fall
Meeting
San Francisco,
California Dec. 13-17, 2010
NH43B-03 (Invited)
The Earthquake
Early Warning System in Japan
Mori,
J. and M. Yamada
In
Japan, the earthquake early warning system (Kinkyu Jishin Sokuhou in Japanese)
maintained by the Japan Meterological Agency (JMA)
has been in operation and sending pubic information
In
Japan, the earthquake early warning system (Kinkyu Jishin Sokuhou in Japanese)
maintained by the Japan Meterological Agency (JMA)
has been in operation and sending pubic information@since
October 1, 2007. Messages have been broadcast on television and radio to warn
of strong shaking to the public. The threshold for broadcasting a message is an
estimated intensity of JMA 5 lower, which is approximately equivalent to MM VII
to VIII. During the period from October 2007 through August 2010, messages have
been sent 9 times for earthquakes of magnitude 5.2 to 7.0. There have been a
few instances of significantly over-estimating or under-estimating the
predicted shaking, but in general the performance of the system has been quite
good. The quality of the detection system depends on the dense network of
high-quality seismometers that cover the Japanese Islands. Consequently, the system
works very well for events on or close to the 4 main islands, but there is more
uncertainty for events near the smaller and more distant islands where the
density of instrumentation is much less The Early Warning System is also tied
to an extensive education program so that the public can react appropriately in
the short amount of time given by the warning. There appears to be good public
support in Japan, where people have become accustomed to a high level of fast
information on a daily basis. There has also been development of a number of
specific safety applications in schools and industry that work off the backbone
information.
T53E-03
Temperature
Measurements in the WFSD-1 Borehole Following the 2008 Wenchuan
Earthquake (Mw7.9)
Mori,
J., H. Li, H. Wang, Y. Kano, J. Pei, Z. Xu, E.
Brodsky
We made temperature
measurements across the Yingxiu-Bechuan fault which
ruptured during the 2008 Wenchuan, earthquake
(Sichuan, China), to try to determine the level of frictional stress during the
earthquake. The measurements were
made in a borehole that penetrates the fault at a depth of about 590 meters.
The surface rupture of the fault close to the drill site was about 7 meters of
oblique thrust movement. Temperature profiles were taken in a cased borehole
starting in October 2009, which is about 18 months following the earthquake.
Repeated observations were done at intervals of one to several months. The
observations were made by slowly lowering and raising high-resolution
temperature sensors in the borehole. The measured thermal gradient is about
0.021 degrees per meter, with a noise level of about 0.01 degrees. Multiple
profiles were averaged together to reduce the noise level of the results.
Analyses of the
results show a small temperature signal of less than 0.03 degrees across the
fault at the location of the inferred rupture plane of the recent earthquake.
If this is the residual frictional heat from the earthquake, it implies quite
low values of the dynamic friction for this portion of the fault.
S21D-05
(Invited)
Subsurface Velocity Changes during
Strong Shaking as Seen from Deconvolution
method (Invited)
Yamada,
M., J. Mori, S. Ohmi
We apply a deconvolution method to a strong motion dataset recorded at
the surface and in boreholes in northeast Honshu, Japan. We try to characterize
the nonlinear effects of the subsurface soil during strong shaking and show the
change of the subsurface velocity structure during the shaking.
The deconvolved waveforms reflect the subsurface velocity
structure, and their horizontal and vertical components correspond to S- and
P-wave, respectively, traveling from the borehole to the ground surface. The
strong motion records with smaller values of peak acceleration do not include
significant non-linear effects, so the deconvolved
waveforms of the observed accelerations can be well simulated by the program SHAKE91.
For high acceleration
motions during the shaking of two separate earthquakes, large reductions of
near-surface velocities are seen. In results for the 2008 Iwate-Miyagi Nairiku earthquake, the large high frequency ground motions
over 4g at one near-source station, caused a non-linear response of the soil,
and the reduction of the average shear wave velocity reached 24%. This
corresponds to a stiffness change of over 75%. The soil properties and the
stiffness coefficient which changed during the shaking did not fully recover
after the shaking, leaving a static change.
S52B-02
Supershear Rupture for the 2010
Qinghai, China Earthquake
Wang,
D. and J. Mori
A
moderately large (Mw6.9) strike-slip earthquake in eastern Qinghai province,
China occurred on April 13, 2010 and caused extensive damage to structures with
over 2200 deaths. The severe ground motions
and resultant damage in the town of Yushu may be at
least partially attributed to the extremely fast speed of the rupture front as
it propagated along the fault toward this location. A nearfield
seismogram recorded at station Yushu clearly
documents that the rupture speed is faster than the S velocity. From analyses
using both near-field and teleseismic data, we
estimate the very fast speed to be 4.6 to 5.4 km/sec, depending on the length
of the super-shear segment. The higher estimate is close to, or possibly
greater than the local P velocity. We examined teleseismic
records for this earthquake using an empirical Green function deconvolution of the P waves of teleseismic
records, we can identify two pulses of high frequency radiation that show the
rupture directivity toward the southeast. The two high frequency centroids were
generated from fault segments that are 6.5 km and 41.8 km southeast of the
epicenter, respectively. We suggest that the sources of high frequency waves
are related to the change of rupture velocity to supershear
speed.
S41A-1989
Improved Seismic Velocity Structure in
Southwestern Japan Using Pronounced sP phases
Hayashida,
T., F. Tajima, J. Mori
In
southwestern Japan the Philippine Sea plate (PHSP) subducts
along the Nankai trough and this subduction
causes the megathrust earthquakes in the Nankai seismic zone as well as large intraslab
and inland earthquakes in the vicinity. The dip angle of the PHSP varies
significantly along strike. In this region the sP phase is widely observed and
its amplitude sometimes becomes larger than that of the direct S wave. This suggests that the phase
could control the peak ground velocities and be a significant factor in
evaluating regional seismic hazards. We previously showed that the arrivals of
this strong phase are explained by incorporating the structure with shallow
bedrock depths in the velocity model, and presented 2D seismic velocity models.
The 2D models derived for profiles between earthquake hypocenters and
observation stations represent the configuration of the subducting
PHSP and the depth variation of the Conrad and Moho
discontinuities (Hayashida et al., 2010). Here, we present a 3D seismic velocity model that
accounts for observed waveforms at a number of local stations where the
pronounced sP
phase was recorded. We present the results of finite difference modeling for
the observed seismograms for a major intraslab
earthquake (2001/3/26 Mw5.1,
h = 46 km) using the e3d code (e3d;
Larsen and Schultz, 1995). First we calculated synthetics using a simple
layered structure (Asano et al., 1986) to fit the arrival times and amplitudes
of sP
phases, and then the P- and S-wave arrivals by tuning the slab
configurations and the Conrad and Moho depths. At an
early stage of 3D modeling we referred to the travel time tomography model
(Nakajima and Hasegawa, 2007) and receiver function
images (e.g. Shiomi et al., 2006; Ueno et al.,
2008). The results show that the dip angle of the PHSP beneath the region
varies significantly along the trench strike, and the agreement between data
and synthetics varies among the models. At stations located in the north and
west direction to the epicenter, the synthetics calculated with the improved
layered model generally agree with the data in the frequency range between 0.1
and 0.5 Hz. On the other hand, at stations located to the east and south of the
epicenter, the agreement was improved by including the slab configuration in
the structure since P and S waves propagate within the slab in the
direction. In addition, at stations located on the thicker subsurface soil
layer (~400 m), the reproduction of sP phase amplitudes and coda durations were improved by incorporating
the subsurface structure model by the National Research Institute for Earth
Science and Disaster Prevention (2010). The constructed velocity model with
detailed features associated with the slab and crust configuration provides a
better assessment of strong ground motions in this region.
NH11C-03 (Invited)
Drilling into Faults Quickly After Earthquakes
Brodsky, E, J. Mori, P. Fulton
What will it take to advance from our current empirical model
of earthquake initiation and fault slip, to a full physics-based understanding
of the rupture process? We need to know the absolute stress levels on the fault
during an earthquake, how the stresses recover afterwards to prepare for the
next event, how one earthquake promotes or inhibits another, and how the
material properties of a particular fault affect its propensity to fail
catastrophically, catastrophically, rather than creep. Immediately after a
large earthquake, there is an opportunity to gain crucial information to fill
these gaps in knowledge. For about two years after a major earthquake, the
fault is observably changing and a deep borehole can capture measurable
signals. For instance, the strength of faults and their time and slip
dependence are generally unknown, especially for large displacements and high
slip velocity. Current laboratory evidence suggests that friction could drop
dramatically during an earthquake, but the actual fault friction levels of a
large earthquake have never been measured. Temperature profiles across the
fault are the most direct way to quantify coseismic
friction. Because most of the frictional resistance is dissipated as heat, any
temperature increase on the fault at the time of the earthquake is potentially
interpretable as a cumulative measure of frictional heat generation during
slip. To obtain the largest and most unambiguous signal possible, it is
critical to record these measurements both soon after earthquake slip, and at depths where shear stress (a function of the
effective normal stress and the effective coefficient of friction) is
sufficiently large to generate an observable temperature anomaly. Model
calculations suggest that a borehole drilled to 2 km depth within 1.5 years
after an earthquake with >1 m surface displacement should be sufficient to
observe a resolvable temperature signal. Similar constraints apply for other
major data needs. Combining the constraints results in a preferred timetable of
drilling initiating within 6 months after the earthquake and intersect
the fault at 2 km depth within 1.5 years. Although major advances in earthquake
physics projects have been made from previous rapid drilling projects on the Nojima, Chelungpu and Wenchuan Faults, a hole that meets these more stringent
target requirements has not yet been completed.
S43D-04
A closer
look at foreshock-mainshock occurennces
in Japan
Smyth, C W, J. Mori, M. Yamada
It is currently impossible to
declare if an arbitrary earthquake is a foreshock in a real time setting.
However, using the methods described in Jones (1985) it is possible to give a
probabilistic assessment that any earthquake will be followed by a larger
earthquake, that is, the probability that any earthquake is a foreshock. Almost
25 years after Jones (1985) published the study of earthquake probabilities in
southern California, we apply the same methodology to Japanese catalog data. We
use recent data, where the magnitude of completeness is low, and seek the probability
that any M≥3 earthquake will be followed by a larger event in the subsequent
days and immediate area. We also consider the effect of dividing the area into
onshore and offshore regions. We find our results to be very similar to those
obtained previously with Californian data. For example, approximately 5 percent
of M≥3 earthquakes are followed by a larger earthquake in the immediate future
and vicinity within Japan, similar to the 6 percent found with the southern
Californian data. Also, similar to the previous study of Jones (1985), we find
the magnitude difference between the foreshock and the mainshock
is more likely to be small than large. We therefore infer that when considering
M≥3 mainshocks, the distribution of the magnitude
differences between the foreshock-mainshock pairs is
not uniform. In contrast to our results, other authors have found that the
magnitude difference between the foreshock and the mainshock
is equally likely to be large as to be small (Agnew and Jones, 1991; Reasenberg 1999). These authors studied larger magnitude
ranges, and allowed a smaller threshold magnitude for foreshocks. We explore
the discrepancy between these studies, using both Japanese and worldwide data,
to discern if it is purely an artifact of study design, or if the magnitude
difference between a foreshock and mainshock is
dependent on foreshock magnitude.
2010
Seismological Society of Japan Fall Meeting
Hiroshima,
October 27-29, 2010
B31-06
Supershear Rupture for the 2010
Qinghai, China Earthquake
Wang,
D. and J. Mori
D12-05
Detection
of August 7, 2010 Fireball Trajectory from Seismic Recordings
Yamada,
M. and J. Mori
P1-49
Characteristics
of Aftershock Sequences from Recent Moderate-sized Earthquakes of Onshore Japan
Mori,
J.
We looked at the spatial
and temporal distributions for 6 recent moderate earthquakes that occurred at
shallow depth onshore of Japan and were well recorded by the regional networks.
These events are the 2000 Western Tottori (Mw 6.7), 2004 Niigata Chuetsu (Mw
6.6), 2005 Fukuoka (Mw 6.6), 2007 Noto Peninsula (Mw
6.7), 2007 Niigata Chuetsu-oki (Mw 6.8), and 2008
Iwate-Miyagi-ken (Mw 6.8). All of these earthquakes are approximately of
similar size, however, the rates of aftershock
activity are quite different. The 2004 Niigata and 2008 Iwate-Miyagi
earthquakes have significantly more aftershocks than the other 4 events. In the spatial locations of the
aftershocks, these two earthquakes have more complex spatial distributions with
more aftershocks occurring away from the mainshock
fault plane. There appears to be a correlation between the rate of aftershock
activity and the spatial complexity of the locations. The sequences with higher
rates of aftershock occurrence may be associated with aftershocks triggered in
a volume around the mainshock. In contrast, for the
other sequences, aftershocks occur mainly in a planar pattern close to the mainshock fault plane.
We also looked at the
early time sequence of the aftershocks for these events. Using continuously
recorded seismograms from nearby borehole stations of Hi-net, aftershocks were
identified and counted. From about one minute following the mainshock
origin time, we estimate that we can identify aftershocks with magnitudes down
to Mj 3.5. For the first few minutes the rate of aftershocks
is quite similar for all of the mainshocks. The
higher rate of aftershocks for the 2004 Niigata and 2008 Iwate-Miyagi
earthquakes appears to begin about 10 minutes after the mainshock.
This suggests that the enhanced triggering of aftershock for these 2
earthquakes is caused by some changes in the aftershock region several minutes
after the mainshock.
P1-55
Relocation
of the Aftershocks of the Suruga Bay Earthquake Using Waveform
Cross-correlations
Kimura, S. and J. Mori
P1-63
Joint inversion using the
waveform data and inSAR data for the 2009 Papua
Indonesia Earthquakes
Norimatsu, K., J. Mori, M.
Hashimoto
P2-33
Converting Foreshock Probabilities to an Alarm
Forecast Model
Smyth, C., J. Mori, M.
Yamada
Often after a large, damaging earthquake, we look back through
seismic catalogs to search for indications that the event was imminent. These
indications may include fluctuations in local seismicity rates, or the more
ambiguous foreshock. It is not possible in a real time setting to determine if
an earthquake is a foreshock, because a foreshock can only be named such after
the occurrence of a main shock. Although we cannot differentiate foreshocks
from background events, it is possible to give a probabilistic assessment that
any earthquake will be followed by a larger earthquake, using the methods
described in Jones (1985).
Jones (1985) studied Californian seismicity to determine the
probability that any given earthquake is a foreshock. The author found that
approximately 6 percent of M≥3 earthquakes were followed by a larger earthquake
within 5 days and 10 kilometers. Similarly, the authors found that 6.5 percent
of M≥5 earthquakes were followed by larger earthquakes. This result is of
merit; M≥5 earthquakes are potentially strong enough to cause structural
damage.
Almost 25 years after Jones (1985) published the study of
earthquake probabilities in California, we apply the same methodology to
Japanese catalog data. We use recent data, where the magnitude of completeness
is low, and seek the probability that any earthquake will be followed by
something larger in the subsequent days and immediate area. We also consider
the effect of dividing the area into onshore and offshore regions. Fig. 1 shows
most main shocks follow foreshocks within a few kilometers and days. We find
that approximately 6 percent of M≥5 earthquakes are followed by a larger
earthquake in the immediate future and vicinity; however this percentage varies
for different areas.
Owing to the abundance of data, various foreshock probability
studies have been carried out with Japanese catalog data (Maeda, 1996; Ogata et
al., 1996; Imoto 2005; Zhuang
et al., 2008). The results presented in these more historical studies are
comparable to our study and show that the occurrence of certain patterns of
earthquakes raises the probability of a larger earthquake. These studies also
suggest various prediction and alarm strategies. Based on the successes shown
in the previous studies over naïve models, and the foreshock probabilities we
obtain from the Japanese catalog data, we propose a simple alarm system based
on foreshocks.
In a recent article, Jordon et al. (2010)
commented that we are now entering an era of operational earthquake
forecasting. Various long term and short term forecast models are under test at
the Collabatory for the Study of Earthquake
Predictability and its regional centers including the Earthquake Forecast
System based on the Seismicity of Japan. We describe how our proposed alarm
model could be tested in this environment and the expected success rate. We
also will describe the importance of the development of such alarm based
models, if we are to truly move towards the stage of operational earthquake
forecasting.
P3-24
Are asperity patterns persistent? Implication from
the 1985 and 2010 Earthquakes Occurred Along the Coast of Chile
Hayashida, T. and J. Mori
5th
National Institute of Meterological Research-Korea
Institute of Nuclear Safety
Joint Workshop
on Earthquake Hazard Mitigation
South Chungcheong, Korea, September 30 – October 1 , 2010
Forecasting
Large Volcanic Eruptions: 1991 Pinatubo, 1994 Rabaul
(Invited)
Mori,
J.
2010
Association of Pacific Rim Universities Symposium
Multi-Hazards
around the Pacific Rim
Beijing,
China, September
27-29, 2008
Statistical
Features for the Aftershocks of the 2008 Wenchuan,
China Earthquake
Mori, J. and C. Smyth
The tens of thousands
of aftershocks from the May 12, 2008 Wenchuan, China
earthquake (Mw 7.9) provide an opportunistic data set for statistical studies of
earthquake occurence. We examine this sequence, especially in
relation to the occurrence of larger aftershocks within a given interval of
time. First, we investigate the Gutenberg-Richter frequency distribution as a
potential forecasting technique. The parameters of the Gutenberg-Richter
distribution are calculated using short periods of time. We then combine well
known models describing aftershock sequences, Omori-Utsu
and ETAS, with the Gutenberg-Richter forecast to attempt a consensus forecast
of the expected number of aftershocks above a designated magnitude. The Omori-Utsu or ETAS parameters are calculated using all available
data, and therefore combining the Gutenberg-Richter predictions with the Omori-Utsu or ETAS forecasts can be considered as creating a
forecast ensemble that contains both short-term and long-term information about
the aftershock sequence. The results are illustrated over a variety of interval
lengths of 10 to 20 days. The results show that the forecasts created by the
windowed Gutenberg-Richter model perform as well as the other more common
aftershock forecasting methods. The ensemble forecasts are also shown to
produce reasonable predictions, and are more accurate than using single methods
when forecasting the number of aftershocks greater than or equal to M5.
We also looked at the
periodicities in the aftershock data. The large number of
small earthquakes provide a good data set for searching for small
triggering effects. Especially for the small events, there is a clear 24 hour
cycle that is likely attributed to the difference in day and night levels of
cultural noise. There is also a 12 hour periodicity which is also probably due
to cultural causes. There were no observable effects from the total eclipse
that passed over the southern part of the aftershock area in July 2009.
European
Geophysical Union General Assembly 2010
Vienna, Austria,
May 2-7, 2010
EGU2010-3913
Temporal
Chantes of Subsurface Velocities during Strong
Shaking
Yamada,
M., J. Mori, S. Ohmi
AGU Chapman Conference
on Giant Earthquakes and Their Tsunamis
Valparaiso,
Chile, May
16-24, 2010
19A-2
Are
Asperities Persistent Features in Repeated Great Earthquakes
?
Mori,
J. and S-C Park
The heterogeneous slip
distributions of great subduction zone earthquakes
show areas of large and small slip on the fault. One unanswered question, is whether or not the region s of large slip
(asperities) are fixed features on the fault plane that have similar large slip
in repeated earthquakes. Along the New Britain Trench of Papua New Guinea, two
great earthquakes (Mw8) ruptured a large portion of the plate boundary in
1971. In the following decades,
several Mw7.5 to 7.9 earthquakes in 1995 and 2000 appeared to have re-ruptured
the same portions of the subduction zone. The distribution of areas of large slip
does not seem to have similar spatial patterns for the re-ruptured areas. This example suggests that the patterns
of slip distribution can change with repeated earthquakes. Another example from the 1968 and 1994 Tokachi-oki earthquakes in Japan seems to show the opposite
case with an asperity pattern that may be similar. We will look at other examples where subduction zone earthquakes have apparently re-ruptured the
same area to investigate if asperities are fixed features on the plate
boundary.
Japan Geoscience
Union Meeting 2010
Makuhari,
Chiba, May 23-28, 2010
SSS012-P08
The Factors Affecting the Rate of Large
Earthquakes on Japanese Island Faults
Smyth, C. and J.
Mori
SSS025-03
Predicting
Aftershocks Using Ensembles Following the May 12 2008 Wenchuan
China Earthquake
Smyth, C. and J.
Mori
HDS023-04
Estimating
On-going Fault Rupture Extent for Large Earthquakes from Strong motion Records
Yamada, M. and J. Mori
SSS013-P12
Relocation
of the Aftershocks of the Suruga Bay Earthquake Using Waveform
Cross-Correlations
Kimura, S. and J.
Mori
SSS015-02
Pronounced
sP Depth Phases Recorded in Southwestern Japan:
Modeling and Implications
Hayashida, T. F. Tajima, J. Mori
DPRI Annual Meeting 2010
Uji, Kyoto
Feb. 23-24, 2010
The 2009 LfAquila
earthquake (M6.3) – Damage and Response to a Moderate Event.
Mori,
J.
A moderate size
earthquake (Mw6.3) occurred in central Italy near the town of LfAquila on April
6, 2009. Despite the relatively small size, the event caused much damage and
killed nearly 300 people, mainly due to the old construction of buildings in
the region. The earthquake occurred on a normal fault that strikes in the
northwest direction and dips downward toward the southwest. There was a strong
aftershock sequence that included 7 events M5.0 or greater. Since this region
has had sequences of moderate earthquake in the past, the strong aftershocks
raised concern that other damaging earthquakes might soon happen. However, no other large events occurred
within the following several months.
Prior to the
earthquake, there was a significant increase of small earthquakes in the area,
many of which were felt by the residents. There were also two M4 earthquakes during
the week before the mainshock. An amateur earthquake
prediction in March alarmed the public and 5 days before the mainshock occurred, government officials announced that
there was no scientific basis for the earthquake prediction. These events
raised interesting issues about earthquake predictions and public information
concerning natural hazards.
5th Kyoto University Southeast Asia Forum
Conference of the Earth and Space Sciences
Bandung, Indonesia, January 7-8, 2010
Can We Predict the Next Great Earthquake ?
(Invited)
Mori, J.