Top PDF Body-Wave and Earthquake Source Studies

Body-Wave and Earthquake Source Studies

Body-Wave and Earthquake Source Studies

formulate the seismic ray theory on a m ore rigorous basis. on the vector wave equation in an inhomogeneous medium. Within the ray approximation, attenuation of body w[r]

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A Bayesian Approach to Earthquake Source Studies

A Bayesian Approach to Earthquake Source Studies

Chapter 6 Closing Remarks In geophysics, and especially in earthquake seismology, most of the inverse problems we deal with are under-determined. If you come away with nothing else from this work, I hope you will appreciate why Bayesian analysis is a more appropriate way to handle these problems than traditional optimization approaches. Regardless of its utility, Bayesian analysis has until now simply not been a practical option for geophysical modeling. It is too computationally intensive for problems with a large number of free parameters or problems whose forward models are themselves expensive to calculate. I therefore designed and implemented a parallel sampling technique, CATMIP, which allows us to tackle problems as complex as kinematic finite fault modeling. It is worth emphasizing that while I have used this algorithm to produce earthquake source models, the sampling algorithm is independent of the forward model, and can be used for any inverse problem.
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Source rupture process of the 2003 Tokachi oki earthquake determined by joint inversion of teleseismic body wave and strong ground motion data

Source rupture process of the 2003 Tokachi oki earthquake determined by joint inversion of teleseismic body wave and strong ground motion data

International Institute of Seismology and Earthquake Engineering, Building Research Institute, 1 Tatehara, Tsukuba, Ibaraki-ken 305-0802, Japan (Received November 30, 2003; Revised February 23, 2004; Accepted February 29, 2004) The spatio-temporal slip distribution of the 2003 Tokachi-oki, Japan, earthquake was estimated from teleseismic body wave and strong ground motion data. To perform stable inversion, we applied smoothing constraints to the slip distribution with respect to time and space, and determined the optimal weights of constraints using an optimized Akaike’s Bayesian Information Criterion (ABIC). We found that the rupture propagates mainly along the dip direction, and the length of the rupture area is shorter than its width. The mean rise time in the shallow asperity is significantly longer than that in the deep asperity, which might be attributed to variable frictional properties or lower strength of the plate interface at shallower depths. The average rupture velocity of deep asperity extends to the shear-wave velocity. The derived source parameters are as follows: seismic moment Mo = 1.7× 10 21 Nm (Mw 8.0); source duration = 50 sec. We also estimated the shear stress change due to the mainshock on and around the major fault zone. It appears that many aftershocks on the plate boundary took place in and adjacent to the zones of stress increase due to the rupture of the mainshock.
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Surface Wave Propagation and Source Studies in the Gulf of California Region

Surface Wave Propagation and Source Studies in the Gulf of California Region

Earthquake sources, propagation paths, observed fundamental and first higher mode (Sn) Rayleigh wave dispersion, and crustal model fit to the data for the central [r]

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Earthquake Statistics and Earthquake Research Studies in Pakistan

Earthquake Statistics and Earthquake Research Studies in Pakistan

Earthquake Prediction studies is not getting much attention and hence is not an active research field in Pakis- tan as in other countries prone to earthquake, this is because most of the seismologists in Pakistan take earth- quake prediction as fool’s paradise and focus only on the earthquake hazard studies and therefore in the past, few hazard maps based on probabilistic approach which is defined as the likelihood for a specified Peak Ground Acceleration (PGA) value to be exceeded within a certain time interval are available for the region but unfortu- nately the drawback of this approach is that catalogue completeness is very essential parameter in this technique and we may be underestimating the seismicity in those seismogenic zones where the strongest occurring event is not reported in the catalogue, in addition to this, other aspects largely overlooked in this approach are that the effects of crustal properties on attenuation are neglected and the ground motion parameters are derived from overly simplified attenuation functions, and a partisan solution to this problem is field studies aimed at the rec- ognition of the seismogenic potential of major active faults. As shown in this paper, it is required that reasons for main destruction due to these earthquakes may be addressed properly like implementation of building code especially in areas lying on the active faults as many thickly populated major cities of Pakistan like Islamabad, Quetta, Muzaffarabad etc. lie on active faults that are source of many destructive earthquakes in the past. It is also immediate need that individual as well as Government supported Earthquake safety and preparedness train- ing programs should be organized in order to save lives and properties.
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Few-body Studies at the High Intensity γ-Ray Source (HIγS)

Few-body Studies at the High Intensity γ-Ray Source (HIγS)

Abstract. The HIγS facility is making it possible to perform studies of few body systems at a new level of accuracy and precision. A study of the photodisintegration of the deuteron using 100% linearly polarized beams at 14 and 16 MeV has determined the splittings of the three p-wave amplitudes involved in this process for the first time. These results show that the relativistic contributions, which when included in the theory lead to a positive value of the GDH integrand above 8 MeV, are valid. The near threshold data on the photodisintegration of the deuteron provide results which are used to extract the forward spin-polarizability of the deuteron for the first time. The experimental value is in good agreement with a recent effective field theory calculation. Measurements of the absolute differential cross section of the 3 He(γ,n)pp reaction have been completed at three γ-ray energies.
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The ISC Bulletin as a comprehensive source  of earthquake source mechanisms

The ISC Bulletin as a comprehensive source of earthquake source mechanisms

The ISC has a mandate to collect as many parametric data as possible from various sources around the world and make it freely available to the seismological as well as broad geoscience communities. As a result, the magnitude range of earthquakes covered by available mechanism solutions is larger than individual global catalogues such as GCMT or NEIC. However, this feature inevitably leads to a higher het- erogeneity in the solutions due to different methods adopted by each provider. Thus, users are advised to be aware of the techniques being used in the computations of the various source models in the ISC Bulletin. For example, centroid- based mechanism solutions should be used together with cen- troid locations, since (i) both the centroid mechanism and centroid location are parts of the same output and (ii) sub- stantial differences may exist among centroid locations and standard hypocentre locations fitting the observed phase ar- rival times of body waves. To facilitate this the CSV for- mat provided by the online ISC Bulletin indicates whether a mechanism solution is centroid or hypocentre. Source mech- anisms obtained from pre-determined standard hypocentre locations can be used together with the provider’s hypocentre solution or the prime hypocentre solution in the ISC Bulletin. However, large differences in depth may be present in some cases among the prime hypocentre solution and the solution provided by the mechanism’s agency. Moreover, information regarding the quality of the obtained mechanism solutions such as the number of stations being used and/or errors in the obtained source models is also provided in the ISC Bul- letin where available from the reporting agency. The latter is more common in moment tensor solutions. Detailed quality information is routinely provided for the ISC focal mecha- nism solutions, both in the comments section in the online ISC Bulletin as well as by clicking on the “ISC Focal Mech- anism” logo on the top of the online bulletin.
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Topics in gravitational-wave astronomy: Theoretical studies, source modelling and statistical methods

Topics in gravitational-wave astronomy: Theoretical studies, source modelling and statistical methods

Other methods seek to reduce the number of inner products in a grid-based search through template bank compression, i.e. the reduced-basis representa- tion of a large template bank by a smaller set of templates [164–166]. In a recently proposed method of template bank compression [167], binary labelling is used to define a non-orthogonal basis that maximises compression losslessly (in the sense of perfect signal recovery without noise). This idea is fully general and admits a much higher compression rate than existing meth- ods based on the eigenvalue structure of the template bank, but comes with significant penalties to detection sensitivity and localisation accuracy in the presence of detector noise. The method as originally described also suffers from an arbitrarily asymmetric treatment of templates, as well as a restrictive level of compression that limits its practicality to high-SNR signals. While the binary labelling method might be useful in the context of LISA (where source SNRs are potentially higher than for ground-based detectors), its practical ap- plicability to GW data analysis remains undeveloped and hence unclear.
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Rapid Assessment of Earthquake Source Characteristics

Rapid Assessment of Earthquake Source Characteristics

With accurately determined source characteristics, the next step is to investigate how quickly and accurately these results can be obtained within a short time after an earth- quake occurs, on the order of seconds after the first P arrival. For the 2014 shallow event, we selected a group of six nearby stations, which are within an epicentral distance of 20 km and form a close ring of seismic recording for the shallow event, providing good azimuthal coverage (Fig. 4 ). The P wave reached these stations within 4 s after the origin time, whereas the S wave arrived at the stations within 8 s. By ap- plying CAP on waveforms recorded at only these six stations, source parameters evolve as more and more seismic data are available for inversion. Eventually all parameters match with the network mechanism. With only 3 s of incoming waveform, strike and dip inversions are already within 10° from the net- work mechanism (Fig. 5a ). The waveform cross correlations are also above 90% for most of the vertical and radial com- ponents at stations. Furthermore, moment magnitude differs by less than 0.1 from the network inversion estimate. Because focal depth can only be accurately determined after the arrival of S waves, we only assume an average hypocenter depth in the area ( ∼7 km) for the 3 and 6 s inversion. With 10 s of waveform, including the incoming S phase, we then also per- form a grid search on focal depth. For the deep event in 2009, a slightly different group of stations are selected, due to the difference in event location. Station CLT is clipped in this case, given its < 2 km distance from the source. Nonetheless, a similar level of accuracy is obtained from the inversion (Fig. 5b ). The 2014 and 2009 earthquakes are constrained at a depth of 3.5 and 14 km, respectively, which are almost identical with network depth. As a check, we reran the 3 and 6 s inversion with the updated focal depths, and similar results are obtained. This indicates that preliminary seismic moment and focal mechanism estimates are not heavily de- pendent on focal depth as demonstrated in Figure 5 .
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Three dimensional S wave attenuation structure in and around source area of the 2018 Hokkaido Eastern Iburi Earthquake, Japan

Three dimensional S wave attenuation structure in and around source area of the 2018 Hokkaido Eastern Iburi Earthquake, Japan

Ryoichi Nakamura * and Takahiro Shiina Abstract We investigate S-wave attenuation (Qs) structure in and around Hokkaido, Japan, including the source area of the 2018 Hokkaido Eastern Iburi Earthquake (M 6.7) and its aftershocks. From the strong-motion seismograms recorded in the nationwide seismograph network in Japan, we compute spectrum amplitude at 1–10 Hz with every 1 Hz and then estimate Qs structure by adopting tomographic inversion technique. The obtained Qs structure suggests that lateral variations of Qs are remarkably formed in the study areas. The low-Qs anomalies distributing north to south are imaged in both sides of the Hidaka mountain range which is built in the central Hokkaido. These characteristics struc- tures of Qs are extended from the ground surface to depths by about 50 km, indicating that heterogeneous struc- tures resulted from the collision of the Kuril and northeastern Japan arcs develop at the depth ranges. Around the source area of the 2018 Hokkaido Eastern Iburi Earthquake, the abrupt changes of Qs values are identified. The 2018 Hokkaido Eastern Iburi Earthquake and its aftershocks seem to be arraigned on the high-Qs zones, whereas the low- Qs anomalies are also imaged next to the high-Qs zones. The boundary of the low- and high-Qs zones lies with near vertical, corresponding to aftershock distributions of the 2018 Hokkaido Eastern Iburi Earthquake. This agreement would propose that the heterogeneities formed due to the arc–arc collision would characterize faulting processes in the main shock of the Hokkaido Eastern Iburi Earthquake and the activities of its aftershocks.
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Stress state in the upper crust around the source region of the 1891 Nobi earthquake through shear wave polarization anisotropy

Stress state in the upper crust around the source region of the 1891 Nobi earthquake through shear wave polarization anisotropy

Yoshihiro Hiramatsu 1* , Takashi Iidaka 2 and The Research Group for the Joint Seismic Observations at the Nobi Area 2 Abstract We investigate shear wave polarization anisotropy in the upper crust around the source region of the 1891 Nobi earthquake, central Japan. At most stations, the orientation of the faster polarized shear wave is parallel to the axes of the maximum horizontal compressional strain rate and stress, indicating that stress-induced anisotropy is dominant in the analyzed region. Furthermore, near the source faults, the orientation of the faster polarized shear wave is oblique to the strike of the source faults. This suggests that microcracks parallel to the strike of the source fault, which would be produced by the fault movement of the Nobi earthquake, have healed with the healing of the faults. For stress-induced anisotropy, time delays normalized by path length in the anisotropic upper crust as a function of the differential strain rate are coincident with those in the inland high strain rate zone, Japan. These data, together with those of a previous study, show that the variation in the stressing rate, estimated from shear wave splitting, is close to that estimated from geodetic observation. This implies that the variation in the stressing rate in the brittle upper crust is linked to that in the strain rate on the ground surface.
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Source Characteristics of the 2012 Ahar Varzaghan Earthquake

Source Characteristics of the 2012 Ahar Varzaghan Earthquake

3. Source Parameters of Mainshock Using the inversion technique developed by Kikuchi the body waves of Ahar-varzaghan earthquake recorded by GDSN stations were inverted to their sources to investigate the source mechanism. The P waveforms of 30 sta- tions with epicentral distances between 30 and 100 degrees were used for this study [19]. The locations of se- lected seismic stations are given in Table 1. The records with duration of 60 seconds were inverted with a sam- pling interval of 1.0 second. Both the observed and synthetic Green’s functions for all the stations were equa- lized to GDSN seismograms with the same gain [20]. In calculating the synthetic wavelet for a point dislocation we used the Jeffreys-Bullen A model [21]. First, a source time function of trapezoid shape having rise time of 3 seconds and process time of 20 seconds was best fitted. Then, with the fixed source time function, the data was inverted for several source depths. The residual error was minimized for the depth of 5 - 15 kilometers. This
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Broadband modeling of earthquake source and mantle structures

Broadband modeling of earthquake source and mantle structures

both in the time domain and frequency domain. However, NM15 is the most anoma- lous. Thus, it appears that wave propagational effects are playing a dominant role in controlling these shapes and amplitude decays. We choose NM07 as the reference station. Such a choice is similar to analyzing waveforms recorded on basin sites rela- tive to that recorded on hard rock sites (?). We find it is not critical to our analysis since we are primarily interested in modeling the pattern of changes in travel time and amplitude across the transition region between the western Great Plains and the Rio Grande Rift. We pursue this strategy by generating synthetic waveforms from the above tomographic models and compare them directly with observations to evaluate their effectiveness. To demostrate the usefulness of including waveform and amplitude information, we focus first on the transition from the Great Plains to the rift zone where we expect the largest velocity constrast to occur and waveforms to be heavily distorted. In particular, as we will show later, the waveforms are sys- tematically distorted, broadened and the amplitude decreases accordingly. Instead of cross-correlation, we will pick travel time delays, measure waveform amplitude and use them as observables to compare with synthetic ones. Though other features shown in the tomographic image appear interesting as well, we will leave for future analysis. In this paper, we examine tangential SH broadband waveform first since S wave anoma- lies typically show much larger distortions than do P waves. In addition, we perform a suite of synthetic tests to demonstrate the usefulness of broadband waveform and amplitude information in deciphering the location, geometry, and depth extent of a subducting slab. We will further analyze P waveforms in a separate chapter and the joint results will provide important constraints on the physical state and composition of this interesting slab feature beneath the western edge of the cratonic Great Plains near the Rio Grande Rift.
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Imaging the subsurface using induced seismicity and ambient noise: 3D Tomographic Monte Carlo joint inversion of earthquake body wave travel times and surface wave dispersion

Imaging the subsurface using induced seismicity and ambient noise: 3D Tomographic Monte Carlo joint inversion of earthquake body wave travel times and surface wave dispersion

model can be inconsistent with surface wave data. Thus it is better to invert for a unified model of velocity and source locations jointly using both types of data. In the real data results, the high velocity anomaly at the location of the southern cluster there- fore may reflect the true structure of the subsurface, e.g., earthquake asperities following previous interpretations (Lees 1990; Eberhart-Phillips & Michael 1998; Chiarabba & Amato 2003; Tajima et al. 2009; Li et al. 2013; Zhang et al. 2013). However, since we still observe subtle multimodil- ities in the joint inversion results, and the real Earth may have a more complex structure, there is still the possibility that the details of the recovered model are obscured by the trade off between source parameters and velocity models. The synthetic test suggests that the trade off mainly af- fects the velocity structure at the location of the southern earthquake cluster, so our results at least remain valid for most of the subsurface.
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Source rupture process of the Papua New Guinea earthquake of July 17, 1998 inferred from teleseismic body waves

Source rupture process of the Papua New Guinea earthquake of July 17, 1998 inferred from teleseismic body waves

A large earthquake (Ms 7.1) occurred off northwest coast of Papua New Guinea (PNG), and a massive tsunami attacked villages to cause a devastating damage. In an attempt to ascertain the tsunami source, we investigate the source rupture process using teleseismic data at IRIS network as well as local data at Jayapura, Irian Jaya, station. The source parameters obtained are: (strike, dip, slip) = (301 ◦ , 86 ◦ , 91 ◦ ); the seismic moment = 4 . 3 × 10 19 Nm (M w = 7.0); the duration of main rupture = 19 s; the centroid depth = 20 ± 5 km; the extent of rupture along the fault strike = 40 km; the average dislocation = 1.8 m; the stress drop = 7.3 MPa. The tsunami magnitude Mt determined from tide-gage data at long distance is 7.5, significantly larger than Ms, so that the PNG earthquake is characterized as a tsunami earthquake. Tsunami earthquakes might have been caused by slow rupture, submarine landslide, and high-angle dip-slip. Our teleseisimic analysis precludes the first two candidates and favors the third one as a source of the present earthquake, although it does not necessarily exclude the possibility of an aseismic landslide induced by the main shock or its aftershocks.
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Source location and mechanism analysis of an earthquake triggered by the 2016 Kumamoto, southwestern Japan, earthquake

Source location and mechanism analysis of an earthquake triggered by the 2016 Kumamoto, southwestern Japan, earthquake

be amplified not by the source and the path effects but by the effect of sediment layers at shallow depth, since monochromatic signals in the amplified later phases are found. For the east–west component, the initial S-phase with large amplitudes is reproduced well from the con- volved waveforms for the five smaller events. For Events 2–5, the second phase of the triggered event (appear- ing 2 s after the initial phase) is also reproduced. The reproduction is also verified for convolved waveforms from a small Mw 3.7 event of the strike-slip type with a slight normal-fault component (Additional file 1: Fig- ure S2) that was rapidly determined by waveform analy- sis and listed in the AQUA CMT database (Matsumura et al. 2006), indicating that the use of intermediate-sized earthquakes (Mw 4.1–5.1) in this analysis is not inap- propriate for Green’s function. However, the second phase is not reproduced by the convolved waveform of only Event 1. Of the five smaller-sized events, the phase in the horizontal component of the convolved wave- form for Event 5 is likely to match that of the triggered event. Although we cannot determine the fault param- eters from our waveform comparisons, we speculate that the source may be located in the northeastern area, near station OIT009, and be a normal-fault type or a normal- fault with strike-slip components.
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Sensitivity of tsunami wave profiles and inundation simulations to earthquake slip and fault geometry for the 2011 Tohoku earthquake

Sensitivity of tsunami wave profiles and inundation simulations to earthquake slip and fault geometry for the 2011 Tohoku earthquake

Katsuichiro Goda 1* , Paul Martin Mai 2 , Tomohiro Yasuda 3 and Nobuhito Mori 3 Abstract In this study, we develop stochastic random-field slip models for the 2011 Tohoku earthquake and conduct a rigorous sensitivity analysis of tsunami hazards with respect to the uncertainty of earthquake slip and fault geometry. Synthetic earthquake slip distributions generated from the modified Mai-Beroza method captured key features of inversion-based source representations of the mega-thrust event, which were calibrated against rich geophysical observations of this event. Using original and synthesised earthquake source models (varied for strike, dip, and slip distributions), tsunami simulations were carried out and the resulting variability in tsunami hazard estimates was investigated. The results highlight significant sensitivity of the tsunami wave profiles and inundation heights to the coastal location and the slip characteristics, and indicate that earthquake slip characteristics are a major source of uncertainty in predicting tsunami risks due to future mega-thrust events.
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Sensitivity of tsunami wave profiles and inundation simulations to earthquake slip and fault geometry for the 2011 Tohoku earthquake

Sensitivity of tsunami wave profiles and inundation simulations to earthquake slip and fault geometry for the 2011 Tohoku earthquake

Katsuichiro Goda 1* , Paul Martin Mai 2 , Tomohiro Yasuda 3 and Nobuhito Mori 3 Abstract In this study, we develop stochastic random-field slip models for the 2011 Tohoku earthquake and conduct a rigorous sensitivity analysis of tsunami hazards with respect to the uncertainty of earthquake slip and fault geometry. Synthetic earthquake slip distributions generated from the modified Mai-Beroza method captured key features of inversion-based source representations of the mega-thrust event, which were calibrated against rich geophysical observations of this event. Using original and synthesised earthquake source models (varied for strike, dip, and slip distributions), tsunami simulations were carried out and the resulting variability in tsunami hazard estimates was investigated. The results highlight significant sensitivity of the tsunami wave profiles and inundation heights to the coastal location and the slip characteristics, and indicate that earthquake slip characteristics are a major source of uncertainty in predicting tsunami risks due to future mega-thrust events.
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Earthquake source characterization using 3D numerical modeling

Earthquake source characterization using 3D numerical modeling

The amplitude anomalies δ ln A i resemble a fairly smooth sine-wave pattern, positive to the west and negative to the east, that can be explained by west-ward propagating rupture (Ben-Menahem, 1961). The time shifts δτ i are near zero for all azimuths at 207 seconds, for both Rayleigh and Love waves. At 420 seconds they are also near zero for westward azimuths, for both wave types, although significantly different from zero in east- ward azimuths. The synthetics arrive as much as 20 seconds earlier than the data in east-ward azimuths for Rayleigh waves, and 40 seconds for Love waves. This general shape of the sinusoidal pattern of time shifts can be explained by a mislocation of the source. The baseline of the sinusoid is then indicative of the source delay relative to the estimated one, here around 15 seconds. The amplitude of the sinusoid is related to the mislocation of the source. This results show that the 400 seconds waves are consistent with a point source that occurs later and further west than the point source consistent with the 200 seconds waves. From this we can immediately expect some sort of asymmetric triangular source time function, with a rapid rise in slip near the epicenter, slowly falling off in time and towards the west. The Harvard CMT was constructed to fit mantle waves of 135 seconds and longer and does a very good job of matching the data at 207 seconds. It is interesting, however, that there is such a discrepancy for the longer period data, indicating that the source is not well matched by a point source at 135 seconds and longer.
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Earthquake source parameters that display the first digit phenomenon

Earthquake source parameters that display the first digit phenomenon

earthquake, to avoid sophisticated filtering of events. The af- tershock series is composed of 172 events, located between 12 and 80 km depth and ranging from moment magnitude 4.9 to 9.1; a representation of the aftershock series can be seen in Fig. 4. The colors of the circles clearly show the high dy- namical range reached by waiting times. From this set, the first digit distribution of the seismic moment released M 0 (t ) is remarkable and the waiting times 1τ between aftershocks were found to obey a weak statistical significant first digit anomaly at the 5 % level. Fifth, regarding the tsunami phe- nomenon, we analyzed runup (r) data measured by Mori et al. (2011). This data set comprises 5260 points, each of them representing the maximum height inland reached by the water wave generated by the dislocation in the ocean floor.
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