Top PDF Body-Wave and Earthquake Source Studies

Body-Wave and Earthquake Source Studies

Body-Wave and Earthquake Source Studies

But in the case of a vector boundary value problem as the one we shall be dealing with, the Green's function must be a dyadic, or a vector operator, in order to transform the vector boun[r]

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Source Parameters of the March 31st, 2006, Dorud Earthquake in Iran

Source Parameters of the March 31st, 2006, Dorud Earthquake in Iran

Dahlen [10] and Burridge [11] have calculated far-eld radiation when the initial phase of rupture is a self- similar circular rupture zone and the rupture slows and stops in such a manner that the initial break governs the high-frequency spectral content. Dahlen [9] assumed rupture speeds less than the S-wave velocity; Burridge [11] used rupture propagation at the P - wave velocity appropriate for a purely frictional fault lacking cohesion. Burridge [11] nds P -wave corner frequencies greater than S-wave corner frequencies in 83.7 percent of the focal sphere. Molnar et al. [12] suggested that observations of P - and S-wave corner frequencies could provide a constraint on the various earthquake source models. Again, with the exception of shallow earthquakes, body wave spectra are also preferable for determination of the source dimension, since f 0 is generally in a period range at which surface
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Change of the source mechanism of the main shock of the 2004 off the Kii peninsula earthquakes inferred from long period body wave data

Change of the source mechanism of the main shock of the 2004 off the Kii peninsula earthquakes inferred from long period body wave data

Waveform inversion of long period body wave data was performed to determine the temporal distribution of moment release of the main shock of the 2004 off the Kii peninsula earthquakes. Our result suggests that the source mechanism varied during the rupture, with the first 20 sec dominated by the strike slip component, while a thrust mechanism was predominant between 30–40 sec. The employed dataset has enough resolving power to detect temporal change on such a time scale, and thus our results suggest that this earthquake is a compound event consisting of the two different source mechanisms.
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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

in the same wave shape regardless the station azimuth. On the contrary, a buried double-couple source accompanies de- layed free surface reflections (pP, sP, sS) which can result in the variation of wave shape with respect to the ray direction. Taking these into account, we compare the observed and synthetic records of radial S-waves in Fig. 7. The first col- umn shows the observed waveforms, the second column the synthetic waveforms for a buried double-couple (strike, dip, rake = 301 ◦ , 86 ◦ , 91 ◦ ), and the third column for a surface single-force (azimuth = 198 ◦ , dip = 10 ◦ upward). Since radial S-waves are sensitive to underground structures as to be easily distorted by P-SV conversion, we here restrict our- selves only to an initial portion of S arrival. In Fig. 7, the opposite polarity between S and sS is seen to distort the waveforms observed at southern stations: CAN, TAU and NWAO. Such a feature is well reconstructed by a buried double-couple source but not by a free surface source. Thus the present earthquake is not likely to be modeled by a single force at free surface.
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Dynamic Earthquake Source Modeling and the Study of Slab Effects

Dynamic Earthquake Source Modeling and the Study of Slab Effects

such impulse response functions with different phase shifts. This causes destructive interference which annihilates most of the beam forming energy throughout the rupture, leaving only two peaks at the beginning and end of the rupture (Figure B.2). To demonstrate this destructive interference effect on the imaging of the Gorkha earthquake source specifically, we design numerical experiments that back project the seismic wave generated by our dynamic source models at two typical frequencies used by previous studies (Avouac et al., 2015; Yagi and Okuwaki, 2015; Grandin et al., 2015): a low-frequency component of 0.25 Hz and a high-frequency com- ponent of 2 Hz. In a real implementation of back-projection, researchers usually divide a frequency band into small narrow bands, and integrate the power generated at each band. The two typical frequencies we chose can represent the frequencies around them. We assume an idealized situation in which the receivers are uniformly positioned globally, with high spatial density and high coherency at all inter-station distances. The finite source is represented by multiple point sources whose rupture time is taken from the rough dynamic model. We simulate seismograms produced by the finite source at all stations and then back-project them on the fault. The forward and backward propagator is a time shift operator with the time shift cal- culated using the 1D PREM model. We neglect the amplitude decay so that each receiver contribute to the beam-forming energy with the same weight. As shown in Figure 5.11 B and D, the low-frequency back-projection image has energy patches covering the whole seismogenic depth while the high-frequency image has that con- centrated at the deeper portion of the seismogenic zone. This can be explained by the analysis in appendix A that back-projection energy is concentrated where there are rapid changes of rupture speed or slip amplitude (Figure B.2).
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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

The Qs values at depths of 0–20  km mark remark- ably low along the coastline of the west side of the HMR (Fig.  2). Across this arc–arc collision zone, Iwasaki et al. (2004) investigated the shallow crustal structure of the P-wave velocity (Vp) in detail. According to their con- structed Vp model, the low-Vp, < 4.5  km/s, layers are lying near the ground surface in the west side of the HMR. These layers were interpreted as the thick sedi- mentary layers, and associating features are identified in other geophysical measurements, such as S-wave veloc- ity (e.g., Nishida et  al. 2008), P-wave attenuation (Kita et al. 2014), and electric resistivity (Yamaya et al. 2017). Kinoshita and Ohike (2002) reported that the sediments would affect to reductions of Qs from the studies around the Kanto district, Japan. Thereby, the remarkable low-Qs values would be derived from presences of the thick sedi- mentary layers. At the results of 10  Hz, low-Qs values concentrating to near the ground surface are additionally detected in the east side of the HMR (Fig. 4b–d). Iwasaki et al. (2004) showed the presences of low-Vp layers in the east side too. Thus, the low-Qs zone in the east side of the HMR may also represent the sedimentary layer; how- ever, it would be thinner than in the west side because decreases of Qs are not clear in the low-frequency bands (Additional file 1: Figure S1).
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Earthquake source characterization using 3D numerical modeling

Earthquake source characterization using 3D numerical modeling

At first glance (Fig. 4.6), the waveforms are very well predicted by the synthetics. However, upon closer inspection of the long-period waves in front of the main arrival of the surface waves it becomes clear that the very long-period part of the data is not matched by the synthetics. The observed amplitude discrepancies between east and west are similar as those for the Harvard CMT, indicating that the source does not produce the required amount of directivity. To quantify the differences we again turn to the multi-taper measurements of amplitude differences and time shifts (Fig. 4.7). As observed in the waveforms, the amplitudes towards the west are under predicted, both in the Rayleigh and Love waves. However, the amplitude ratios for the Rayleigh waves do not form a simple sinusoid as a function of azimuth as for the Harvard CMT. Instead, the amplitude ratios are sligtly smaller, or similar, to the southwest than to the southeast, close to zero in the northeast and very large in the northwest. By comparing the amplitude anomalies for model HenryD (Fig.4.7) with the radiation patterns for the point sources (Fig. 4.2) we can guess that this is a result of using the focal mechanism HenryF. This focal mechanism was obtained from body waves and although Henry et al. (2000) state that the difference in misfit to the surface data between HenryD and HenryF is negligible at 135 seconds, this indicates that, in fact, HenryD can predict the longer-period surface waves better. We therefore repeat the simulation using the same slip model but using the surface-wave focal mechanism HenryD. The waveforms for this model are shown in Fig. 4.8 and the amplitude anomalies and time shifts are shown in Fig. 4.9.
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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

The main objectives of the present study are (1) to de- velop stochastic earthquake slip models for the 2011 Tohoku mainshock based on the spectral analysis approach by Mai and Beroza (2002), and (2) to evaluate the impact of earthquake slip and fault geometry on tsunami simula- tion results in terms of near-shore sea surface profiles and inundation height. The investigation focuses on the 2011 Tohoku tsunami because rich datasets from global posi- tioning system (GPS), ocean bottom pressure gauges, tidal measurements, and tsunami inundation/run-up survey re- sults are available for validation of tsunami simulations (Fujii et al. 2011; Maeda et al. 2011; Mori et al. 2011, 2012; Ozawa et al. 2011; Goto et al. 2012; Kawai et al. 2013). In addition, numerous source inversion studies have been conducted using tsunami, teleseismic, and geodetic data to constrain the rupture kinematics of the earthquake (Ammon et al. 2011; Fujii et al. 2011; Hayes 2011; Iinuma et al. 2011, 2012; Lay et al. 2011; Shao et al. 2011; Yamazaki et al. 2011, 2013; Gusman et al. 2012; Sugino et al. 2012; Satake et al. 2013). This event therefore provides a unique opportunity to quantify epistemic uncertainty associ- ated with predictions of the tsunami extent for different scenarios.
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Earthquake Source Characterization Through Seismic Observations and Numerical Modeling

Earthquake Source Characterization Through Seismic Observations and Numerical Modeling

1.5 and 6.5. Due to generally insufficient seismic data resolution and azimuthal coverage, it has been challenging to characterize smaller earthquake sources, and so they are usually regarded as simple radially symmetric rupture at a constant rupture velocity (Brune, 1970; Eshelby, 1957; Madariaga, 1976). In contrast, the ruptures of larger earthquakes ruptures are found to be more complex, often propagate in a unilateral fashion (Henry and Das, 2001; Mai et al., 2005; McGuire et al., 2002). In the past, however, a limited number of studies have shown that small events do have more complicated source processes than typically assumed (Boatwright, 2007; Domański et al., 2002). Fortunately, the rapid densification of regional and global seismic networks and the advancement of computational resources in recent years enable integrated approaches to study the physics of earthquakes, as well as making detailed analysis of small earthquakes possible. On one hand, high- resolution waveform modeling allows in-depth understanding of the kinematics of source processes. On the other, recently developed dynamic rupture simulations consider the effect of seismic wave interactions and are capable of producing realistic rupture behavior that can be compared to observations, providing insights into the fundamental physics that drives what we see on real faults. Furthermore, numerical modeling also bridges the gap between tiny laboratory earthquakes and megaearthquakes ( M w > 9) in nature.
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Electromagnetic signals related to incidence of a teleseismic body wave into a subsurface piezoelectric body

Electromagnetic signals related to incidence of a teleseismic body wave into a subsurface piezoelectric body

In the previous paper (Ogawa and Utada, 2000), we ob- tained an analytic expression for the piezoelectric signals due to a fault motion of an earthquake, and numerically evalu- ated the signal behaviors in a uniform whole space. One of the most important conclusions obtained by this work is that observation of such signals will reveal anisotropy of the medium at the earthquake source region, though detection of such signal will be quite difficult. On the other hands, it is claimed that crustal rocks will not be piezoelectric in general, for the observational facts that electric measurements in the granite-rich area do not record signals associated with inci- dence of teleseismic waves (Johnston, 1998, personal com- munication). Obviously, quantitative discussion is necessary to answer the question about the absence of teleseismically induced piezoelectric signals. It is because detectability de- pends on signal to noise ratio, i.e., comparison between ex- pected signal intensity and both the resolution of the installed measurement system and the noise level at the observation point are indispensable.
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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

On September 26, 2003 September 25, 2003 at 19:50 (GMT), a great thrust earthquake occurred off Tokachi (Tokachi-oki), Hokkaido, Northern Japan. Two peo- ple went missing and more than 800 people were in- jured. The earthquake information initially provided by the U.S. Geological Survey (USGS) is as follows: origin time = 25/07/2003 19:50:06 (UTC); epicenter = 41.78 ◦ N, 144.86 ◦ W; depth = 27 km; moment magnitude (M w ) = 8.1. In the Tokachi-oki region, the Pacific plate subducts toward N60 ◦ W beneath the Hokkaido region from the Chishima (Kuril) Trench at a rate of about 80 mm/year (DeMets et al., 1990), where large and great interpolate earthquakes oc- curred on 1952 (Ms 8.2), 1958 (Ms 8.1), 1969 (Ms 7.8), and 1975 (Ms 7.4). The tectonic settings and the source areas of these great earthquakes are displayed in Fig. 1. Figure 2(b) shows the aftershocks during one-week after the main-shock determined by the Japan Meteorological Agency (JMA) and the focal mechanism of the mainshock determined by the present study. The mainshock mechanism is consistent with tectonic stress buildup on the interplate boundary.
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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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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

models for the broad geoscience community. Thus, only gen- eral suggestions can be given without attempting or being willing to discriminate the data in the ISC Bulletin into right or wrong. Users of the bulletin should keep in mind that dif- ferent techniques are based on different data (first motion polarities, body wave amplitude ratios, body/surface wave modelling), and as a result they weight differently various episodes in the rupture history which ultimately can have a strong effect on the final solution. For example, slip takes place across seismic faults that are not necessarily planar, but their orientation can vary with length. Moreover, the use of local/regional or teleseismic data can be another component of source model variations, and in conjunction with the un- certainties in velocity models that are being used to simulate the wave propagation in the Earth’s interior it is advisable to take into consideration the details of the methodologies being used by different source mechanism providers.
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Coupling coefficient, hierarchical structure, and earthquake cycle for the source area of the 2011 off the Pacific coast of Tohoku earthquake inferred from small repeating earthquake data

Coupling coefficient, hierarchical structure, and earthquake cycle for the source area of the 2011 off the Pacific coast of Tohoku earthquake inferred from small repeating earthquake data

The spatial distribution of interplate coupling along the Japan Trench was investigated based on small repeating earthquake data. The number of small repeating earthquake groups in areas of large coseismic slip during the 2011 Tohoku earthquake is relatively small, which probably in- dicates that strong coupling existed in the area before the large event occurred. The interplate coupling coefficient in the coseismic slip area was found to be high (≥0.5), and this area seems to be bounded by weakly-coupled regions to the south (south of the NE limit of the PHS) and to the north of the coseismic slip area. This estimation, and the occur- rence of the M 9.0 earthquake, suggest that the seismic cou- pling in the area was stronger than previously thought. A high coupling coefficient is estimated, even near the trench, which could act as the source of the large tsunami which accompanied the present earthquake. The coupling coef- ficient in the coseismic slip area shows that some of the slip deficit was released aseismically but some part of the relative plate motion was accumulated in the region. The slip deficit which contributed to the 2011 Tohoku earth- quake was estimated to have accumulated during a period of 260–880 years from the average coupling coefficient in the source area (0.5–0.8), the interseismic moment release rate, the seismic moment of the 2011 earthquake and the as- sumed afterslip of the 2011 earthquake. The asperities for the 2011 Tohoku earthquake overlap with the source areas of previous M ∼ 7 earthquakes and such M ∼ 7 earth- quakes are not characteristic earthquake in the area. The hierarchical structure of asperities may be the key to under- standing huge earthquakes that encompass several smaller asperities.
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Tsunami source of the 2011 off the Pacific coast of Tohoku Earthquake

Tsunami source of the 2011 off the Pacific coast of Tohoku Earthquake

Fig. 3. (a) Slip distributions estimated by tsunami waveform inversion. The color bars are shown below. The subfault numbers are shown in the northernmost and southernmost subfaults. The star shows the mainshock epicenter. Circles indicate aftershocks within one day after the mainshock (JMA data). Dashed lines indicate regions where the probabilities and size of future subduction-zone earthquakes were estimated by the Earthquake Research Committee (2009). Coastal and offshore stations (the same symbol as Fig. 1) are also shown. (b) Seafloor deformation computed from the estimated slip distribution. The red solid contours indicate uplift with a contour interval of 1.0 m, whereas the blue dashed contours indicate subsidence, with a contour interval of 0.5 m. The light blue and dark green frames show the subfaults with > 2 m slips. The synthetic tsunami waveforms are computed from these two regions (near the trench axis and interplate slip) and shown in Fig. 2.
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Source processes of the 2009 Irian Jaya, Indonesia, earthquake doublet

Source processes of the 2009 Irian Jaya, Indonesia, earthquake doublet

The source characteristics of the 2009 Irian Jaya earth- quake doublet are very similar to the Solomon Islands doublets (Fig. 1 and Table 1), as described by Lay and Kanamori (1980) and Park and Mori (2007). Lay and Kanamori (1980) first noted that large shallow earthquakes in the Solomon Islands and New Britain Islands regions tend to occur in closely related pairs. Events are typi- cally separated by a few hours or several days in time and 50∼100 km in space. This behavior has been attributed to a specific pattern of plate boundary heterogeneity consist- ing of small strong asperities spaced close together. The rupture of one asperity induces high, rapidly accumulated stress concentration in adjacent areas and can generate the second similar event. We expect the same triggering mech- anism to be responsible for the doublet events of the Jan- uary 3, 2009 in Irian Jaya. The distinct nature of this be- havior can be attributed to the complex tectonic configu- ration of the area and implies the existence of localized strong coupling between the lithospheric plates along the New Guinea trench. However, it has to be noticed that even though the asperities of the doublet events of the January 3, 2009 from Irian Jaya are well separated one from the other, there exist a significant overlap in the rupture areas of the first and second events. This may indicate that the actual mechanism of doublet triggering for these events is more
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Re estimation of tsunami source of the 1952 Tokachi oki earthquake

Re estimation of tsunami source of the 1952 Tokachi oki earthquake

The coastal tsunami heights computed from the 2003 Tokachi-oki source model (Tanioka et al., 2004a) repro- duce the general pattern that tsunami heights are larger to the west of Kushiro compared to the east (Fig. 9). However, the amplitudes are smaller than the measured heights. Com- parison of the computed and measured heights (Fig. 10) in- dicates that the computed heights are on the average about a half of the measured heights. For the comparison of ob- served and computed tsunami heights, geometric average K and geometric standard deviation κ, which can be consid- ered as error factor, are often used (Aida, 1978). For 77 measurements made for the 2003 tsunami, K = 2.26 and κ = 1.46, indicating that measured heights are on the aver- age more than twice larger than the computed.
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The one-way wave equation: a full-waveform tool for modeling seismic body wave phenomena

The one-way wave equation: a full-waveform tool for modeling seismic body wave phenomena

One of the primary difficulties associated with waveform inversion is the strong non–linearity of the inverse problem. This non–linearity becomes im- portant when the medium is complicated, but is further aggravated when the data include large–offset or wide–angle data [69]. Large offset transmitted wave data are becoming increasingly prevalent because it has been recognized that they are required to resolve lateral structure [107]. In fact, a recent survey of frequency–domain waveform inversion algorithms has indicated that large off- set transmitted or refracted data are commonly applied in seismic tomographic imaging [107]. The non–linearity of the inversion can be improved by precon- ditioning the data as well as having a good starting model. These starting models are usually obtained from conventional traveltime tomography and so are limited by the asymptotic ray approximation. However, newer methods such as the so–called strongly damped wave equation can be used to compute the first–arrival traveltimes [108] or one–way wave equations to compute the most energetic traveltimes and amplitudes [54]. In theory, the acoustic wide–angle wave equation should be applicable to acoustic full–waveform inversion (and the narrow–angle wave equation for elastic full–waveform inversion) either as a means of generating a starting model or as an approximate elastic wave extrap- olator for the iterative forward and reverse propagation steps. However, the theoretical details of its implementation in waveform inversion have yet to be clarified.
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Source process and near source ground motions of the 2005 West Off Fukuoka Prefecture earthquake

Source process and near source ground motions of the 2005 West Off Fukuoka Prefecture earthquake

The main purpose of this paper is to understand strong motion generation process of these earthquakes. At first, the source process of the 2005 West Off Fukuoka Prefec- ture earthquake is studied using the strong motion seis- mograms obtained by Japanese nation-wide strong motion seismograph networks, K-NET (Kinoshita, 1998) and KiK- net (Aoi et al., 2001). These networks are installed and op- erated by the National Research Institute for Earth Science and Disaster Prevention (NIED). The source process of the largest aftershock on April 20, 2005, is also estimated in the same manner. Relationship between the fault rupture of the mainshock and that of the largest aftershock is discussed. Finally, a three-dimensional ground motion simulation us- ing a finite difference method reveals the spatial variation of ground motions in the near-source area.
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