2010 AGU Fall Meeting
San Francisco, California Dec. 13-17, 2010
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 informationIn 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.
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.
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.
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.
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.
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.
look at foreshock-mainshock occurennces
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
Supershear Rupture for the 2010 Qinghai, China Earthquake
Wang, D. and J. Mori
Detection of August 7, 2010 Fireball Trajectory from Seismic Recordings
Yamada, M. and J. Mori
Characteristics of Aftershock Sequences from Recent Moderate-sized Earthquakes of Onshore Japan
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.
Relocation of the Aftershocks of the Suruga Bay Earthquake Using Waveform Cross-correlations
Kimura, S. and J. Mori
Joint inversion using the waveform data and inSAR data for the 2009 Papua Indonesia Earthquakes
Norimatsu, K., J. Mori, M. Hashimoto
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.
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)
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
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
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
The Factors Affecting the Rate of Large Earthquakes on Japanese Island Faults
Smyth, C. and J. Mori
Predicting Aftershocks Using Ensembles Following the May 12 2008 Wenchuan China Earthquake
Smyth, C. and J. Mori
Estimating On-going Fault Rupture Extent for Large Earthquakes from Strong motion Records
Yamada, M. and J. Mori
Relocation of the Aftershocks of the Suruga Bay Earthquake Using Waveform Cross-Correlations
Kimura, S. and J. Mori
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.
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)