The detailed P-wave velocity structure of the crust in the southern Kanto-Tokai region was analyzed using the tomographic method for seismic refraction survey in this paper. A total of 332 P-wave arrival times received from 13 seismic explosion surveys were used in the analysis. The results indicate that analyses of travel-time curves are probably useful for the evaluation of inverted structures. The lateral heterogeneity of the velocity structure is obviously related to tectonics. The crust in the eastern region is thinner than that in the western region. The Conrad discontinuity obviously fluctuates. The granitic layer is thinner beneath the oceanic region to the east of Oshima. The layer becomes about 16 km thick beneath Suruga Bay. The Conrad discontinuity drops nearly 17 km in depth beneath Suruga Bay, and velocity is relatively low there. The Conrad discontinuity rises 6 km beneath MTL and its vicinity. The Moho discontinuity is located at a depth of around 34 km beneath the region to the west of ISTL and roughly coincides with the upper boundary of the seismic zone due to subduction of the Philippine Sea Plate under the Eurasian Plate. It becomes shallow across the Suruga trough toward the eastern region. The discontinuity is located about 27 km in depth beneath the oceanic region east of Oshima.
{"title":"Crustal Structure in the Southern Kanto-Tokai Region Derived from Tomographic Method for Seismic Explosion Survey","authors":"Zhixin Zhao, R. Kubota, F. Suzuki, S. Iizuka","doi":"10.4294/JPE1952.45.433","DOIUrl":"https://doi.org/10.4294/JPE1952.45.433","url":null,"abstract":"The detailed P-wave velocity structure of the crust in the southern Kanto-Tokai region was analyzed using the tomographic method for seismic refraction survey in this paper. A total of 332 P-wave arrival times received from 13 seismic explosion surveys were used in the analysis. The results indicate that analyses of travel-time curves are probably useful for the evaluation of inverted structures. The lateral heterogeneity of the velocity structure is obviously related to tectonics. The crust in the eastern region is thinner than that in the western region. The Conrad discontinuity obviously fluctuates. The granitic layer is thinner beneath the oceanic region to the east of Oshima. The layer becomes about 16 km thick beneath Suruga Bay. The Conrad discontinuity drops nearly 17 km in depth beneath Suruga Bay, and velocity is relatively low there. The Conrad discontinuity rises 6 km beneath MTL and its vicinity. The Moho discontinuity is located at a depth of around 34 km beneath the region to the west of ISTL and roughly coincides with the upper boundary of the seismic zone due to subduction of the Philippine Sea Plate under the Eurasian Plate. It becomes shallow across the Suruga trough toward the eastern region. The discontinuity is located about 27 km in depth beneath the oceanic region east of Oshima.","PeriodicalId":157777,"journal":{"name":"Journal of physics of the earth","volume":"20 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"1997-12-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"121947424","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Polarization anomalies of surface waves suggest the existence of lateral variations of isotropic and azimuthally anisotropic velocity structures in the upper mantle. We investigate the polarization anomalies of fundamental-mode Rayleigh and Love waves (37 earthquakes, 128 paths) at periods of 5-30 s as recorded by a local four-station network of broadband seismometers in Hokkaido, Japan. The network has been operated by the Research Center for Earthquake Prediction of Hokkaido University since December 1988. Rayleigh waves coming from many back-azimuthal ranges show three types of particle motion anomalies, which are usually called inclined, tilted, and sloping motions. The Rayleigh anomalies observed in the data for the Vanuatu region are mainly caused by the azimuthally anisotropic structure beneath the northwestern Pacific, because the effects of the lateral eterogeneities on the inclined motions are considered to be negligible. The Love waves coming from the earthquakes located near Oregon and California, USA, show anomalous waves in the vertical and radial components. It was expected that the waves were higher-mode Rayleigh waves. We calculate synthetic waveforms with normal modes for an oceanic spherically symmetric Earth model for the August 17, 1991, earthquake off the coast of northern California, which shows significant anomalous Love waves. A comparison of the synthetic and observed waveforms suggests that the anomalous waves are not higher-mode Rayleigh waves and require the Love to Rayleigh conversion. The conversion locations concentrate in and around the Kuril trench region. The Love wave anomalies may be caused by lateral variation in the isotropic or anisotropic structures beneath the Kuril trench region.
{"title":"Polarization Anomalies of Surface Waves Recorded by a Broadband Seismometer Network in Hokkaido, Japan","authors":"R. Kobayashi, I. Nakanishi, S. Tsuboi","doi":"10.4294/JPE1952.45.383","DOIUrl":"https://doi.org/10.4294/JPE1952.45.383","url":null,"abstract":"Polarization anomalies of surface waves suggest the existence of lateral variations of isotropic and azimuthally anisotropic velocity structures in the upper mantle. We investigate the polarization anomalies of fundamental-mode Rayleigh and Love waves (37 earthquakes, 128 paths) at periods of 5-30 s as recorded by a local four-station network of broadband seismometers in Hokkaido, Japan. The network has been operated by the Research Center for Earthquake Prediction of Hokkaido University since December 1988. Rayleigh waves coming from many back-azimuthal ranges show three types of particle motion anomalies, which are usually called inclined, tilted, and sloping motions. The Rayleigh anomalies observed in the data for the Vanuatu region are mainly caused by the azimuthally anisotropic structure beneath the northwestern Pacific, because the effects of the lateral eterogeneities on the inclined motions are considered to be negligible. The Love waves coming from the earthquakes located near Oregon and California, USA, show anomalous waves in the vertical and radial components. It was expected that the waves were higher-mode Rayleigh waves. We calculate synthetic waveforms with normal modes for an oceanic spherically symmetric Earth model for the August 17, 1991, earthquake off the coast of northern California, which shows significant anomalous Love waves. A comparison of the synthetic and observed waveforms suggests that the anomalous waves are not higher-mode Rayleigh waves and require the Love to Rayleigh conversion. The conversion locations concentrate in and around the Kuril trench region. The Love wave anomalies may be caused by lateral variation in the isotropic or anisotropic structures beneath the Kuril trench region.","PeriodicalId":157777,"journal":{"name":"Journal of physics of the earth","volume":"10 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"1997-12-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"126055604","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
The process of the collapse of the dacitic lava dome and the development of pyroclastic flows at Unzen volcano, Japan, were studied using infrasonic, seismic and video records. Characteristic infrasonic and seismic signals were recorded corresponding to the collapse of lava blocks from the dome, the drop of blocks on the slope and the migration of pyroclastic flow on the mountain slope. Small infrasonic and seismic waves are excited when the lava dome starts to collapse. When the lava blocks fall onto the mountain slope and are fragmented, larger waves are excited. This suggests that the seismic waves are generated by the collision of pyroclastics on the mountain slope and that the infrasonic waves are excited by small fractures of the dome and the fragmentation of pyroclastics. Some of the infrasonic signals show an obvious Doppler effect, indicating that the pyroclastic flows emit infrasonic signals during their propagation. The location of dome collapse and the path of pyroclastic flows can be identified and traced by a network of low-frequency microphones. The migrating source of infrasonic signals and probably seismic signals is inferred to be located near the front of pyroclastic flows by comparison with video images. This suggests that the fragmentation of pyroclastics occurs mainly near the front of pyroclastic flows. The speed of pyroclastic flows is estimated as 10-30 m/s from the infrasonic records. The excitation of infrasonic and seismic signals is affected by the topography of the mountain slope. The infrasonic energy is almost the same order as the seismic energy but the ratio of infrasonic to seismic energies increases for larger and more mobile pyroclastic flows. This means that the development of pyroclastic flows is controlled not only by the volume of lava and gravitational force, but also by the explosivity related to the pore gases in the lava.
{"title":"Quantitative Analysis of Pyroclastic Flows Using Infrasonic and Seismic Data at Unzen Volcano, Japan","authors":"H. Yamasato","doi":"10.4294/JPE1952.45.397","DOIUrl":"https://doi.org/10.4294/JPE1952.45.397","url":null,"abstract":"The process of the collapse of the dacitic lava dome and the development of pyroclastic flows at Unzen volcano, Japan, were studied using infrasonic, seismic and video records. Characteristic infrasonic and seismic signals were recorded corresponding to the collapse of lava blocks from the dome, the drop of blocks on the slope and the migration of pyroclastic flow on the mountain slope. Small infrasonic and seismic waves are excited when the lava dome starts to collapse. When the lava blocks fall onto the mountain slope and are fragmented, larger waves are excited. This suggests that the seismic waves are generated by the collision of pyroclastics on the mountain slope and that the infrasonic waves are excited by small fractures of the dome and the fragmentation of pyroclastics. Some of the infrasonic signals show an obvious Doppler effect, indicating that the pyroclastic flows emit infrasonic signals during their propagation. The location of dome collapse and the path of pyroclastic flows can be identified and traced by a network of low-frequency microphones. The migrating source of infrasonic signals and probably seismic signals is inferred to be located near the front of pyroclastic flows by comparison with video images. This suggests that the fragmentation of pyroclastics occurs mainly near the front of pyroclastic flows. The speed of pyroclastic flows is estimated as 10-30 m/s from the infrasonic records. The excitation of infrasonic and seismic signals is affected by the topography of the mountain slope. The infrasonic energy is almost the same order as the seismic energy but the ratio of infrasonic to seismic energies increases for larger and more mobile pyroclastic flows. This means that the development of pyroclastic flows is controlled not only by the volume of lava and gravitational force, but also by the explosivity related to the pore gases in the lava.","PeriodicalId":157777,"journal":{"name":"Journal of physics of the earth","volume":"2014 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"1997-12-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"128185591","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
S-wave coda is a useful tool to investigate high-frequency seismic wave attenuation in the lithosphere. The generation and amplitude decay of S-wave coda were introduced by a single scattering model proposed by Aki and Chouet (1975). The amplitude decay rate with time is defined by the quality factor of the S-wave coda (QC-1), which is investigated widely at various regions by the single scattering model. It is only one-component seismograms that have been used to estimate QC-1 in most studies. This is based on the assumption that the decay of the S-wave coda amplitude recorded on a one-component seismometer is equivalent to the decay of the S-wave coda amplitude which is introduced by the single scattering model. In the single scattering model, S-wave coda is represented by the superposition of single scattered waves which are generated by scatterers distributed randomly and come from any direction to the station. We hereafter call the S-wave coda amplitude expected by the single scattering model the "real coda amplitude." The ground motion of the S-wave coda portion, which consists of the superposition of the scattered waves, has various directions with time. Since the amplitude of the S-wave coda part on a one-component seismogram represents only the projection of the real coda amplitude in the direction of the component, the amplitude on the seismogram depends on the direction of the ground motion. Therefore, it is not trivial that the amplitude decay of a one-component seismogram for a coda part gives the decay of the real coda amplitude (i.e., the assumption). If we have three-component seismograms, we can estimate the real coda amplitude more exactly by vector addition of the amplitudes of the three-component seismograms (hereafter "total vector-amplitude"). In this report, we will check the assumption using real three-component seismic data. We estimate QC-1 from a total vector-amplitude and amplitudes of one-component seismograms, and compare them to investigate QC-1 differences among these amplitudes. Here, we adopt 5 kinds of amplitudes to estimate QC-1 as a one-component amplitude: three of them are the amplitudes of each original component and the other two are the amplitudes of the radial and transverse components, which are constructed by horizontal two-component amplitudes. Furthermore, we produce the horizontal vector-amplitude, by vector addition of the amplitudes for, horizontal two-component seismograms, and measure QC-1. This QC-1 is also compared with the QC-1 measured from one-component amplitudes or total vector-amplitude.
{"title":"Comparison of QC-1 Estimates from Coda Envelopes Constructed from One- and Multi-Component Seismograms","authors":"Y. Mamada, H. Takenaka","doi":"10.4294/JPE1952.45.455","DOIUrl":"https://doi.org/10.4294/JPE1952.45.455","url":null,"abstract":"S-wave coda is a useful tool to investigate high-frequency seismic wave attenuation in the lithosphere. The generation and amplitude decay of S-wave coda were introduced by a single scattering model proposed by Aki and Chouet (1975). The amplitude decay rate with time is defined by the quality factor of the S-wave coda (QC-1), which is investigated widely at various regions by the single scattering model. It is only one-component seismograms that have been used to estimate QC-1 in most studies. This is based on the assumption that the decay of the S-wave coda amplitude recorded on a one-component seismometer is equivalent to the decay of the S-wave coda amplitude which is introduced by the single scattering model. In the single scattering model, S-wave coda is represented by the superposition of single scattered waves which are generated by scatterers distributed randomly and come from any direction to the station. We hereafter call the S-wave coda amplitude expected by the single scattering model the \"real coda amplitude.\" The ground motion of the S-wave coda portion, which consists of the superposition of the scattered waves, has various directions with time. Since the amplitude of the S-wave coda part on a one-component seismogram represents only the projection of the real coda amplitude in the direction of the component, the amplitude on the seismogram depends on the direction of the ground motion. Therefore, it is not trivial that the amplitude decay of a one-component seismogram for a coda part gives the decay of the real coda amplitude (i.e., the assumption). If we have three-component seismograms, we can estimate the real coda amplitude more exactly by vector addition of the amplitudes of the three-component seismograms (hereafter \"total vector-amplitude\"). In this report, we will check the assumption using real three-component seismic data. We estimate QC-1 from a total vector-amplitude and amplitudes of one-component seismograms, and compare them to investigate QC-1 differences among these amplitudes. Here, we adopt 5 kinds of amplitudes to estimate QC-1 as a one-component amplitude: three of them are the amplitudes of each original component and the other two are the amplitudes of the radial and transverse components, which are constructed by horizontal two-component amplitudes. Furthermore, we produce the horizontal vector-amplitude, by vector addition of the amplitudes for, horizontal two-component seismograms, and measure QC-1. This QC-1 is also compared with the QC-1 measured from one-component amplitudes or total vector-amplitude.","PeriodicalId":157777,"journal":{"name":"Journal of physics of the earth","volume":"6 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"1997-12-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"123807447","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
A. Hasemi, T. Matsuzawa, A. Hasegawa, N. Umino, T. Kono, S. Hori, A. Ito, Sadaomi Suzuki, Haruyoshi Ishikawa
We observed three explosions along a 60 km profile in the central part of the Kitakami massif, northeastern Honshu, Japan. Explosion sites and most of the observation sites were located on hard-rock outcrops. Using P-wave first arrivals, the average QP along ray paths and site amplification factors were determined for the frequency range between 6 and 30 Hz based on the amplitude spectra decay with distance. QP increased proportional to fn (n_??_0.9). The difference in amplification factors among hard-rock sites was as much as a factor of five for frequencies lower than 12 Hz and became large at higher frequencies. QS and S-wave site amplification factors were obtained only for 5 and 7.5 Hz. QS was slightly larger than QP, but the difference was not significant. S-wave site amplification factors were more variable than those of P-wave among the stations.
{"title":"Q and Site Amplification Factors of Hard-Rock Region in the Kitakami Massif, Northeastern Japan","authors":"A. Hasemi, T. Matsuzawa, A. Hasegawa, N. Umino, T. Kono, S. Hori, A. Ito, Sadaomi Suzuki, Haruyoshi Ishikawa","doi":"10.4294/JPE1952.45.417","DOIUrl":"https://doi.org/10.4294/JPE1952.45.417","url":null,"abstract":"We observed three explosions along a 60 km profile in the central part of the Kitakami massif, northeastern Honshu, Japan. Explosion sites and most of the observation sites were located on hard-rock outcrops. Using P-wave first arrivals, the average QP along ray paths and site amplification factors were determined for the frequency range between 6 and 30 Hz based on the amplitude spectra decay with distance. QP increased proportional to fn (n_??_0.9). The difference in amplification factors among hard-rock sites was as much as a factor of five for frequencies lower than 12 Hz and became large at higher frequencies. QS and S-wave site amplification factors were obtained only for 5 and 7.5 Hz. QS was slightly larger than QP, but the difference was not significant. S-wave site amplification factors were more variable than those of P-wave among the stations.","PeriodicalId":157777,"journal":{"name":"Journal of physics of the earth","volume":"45 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"1997-12-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"130855473","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
The generalized fractal dimensions are measured for the time series based on two complete earthquake catalogues: one with M≥6 earthquakes occurring in the north-south seismic belt of mainland China during the 1900-1990 period published by Ma et al. (1992) and the other with M≥5.5 earthquakes occurring in southern California, USA during the 1915-1994 period compiled by Press and Allen (1995). The log-log plot of Cq versus t, where Cq(t) is the generalized correlation integral and t is the interoccurrence time in years between two events, at positive q shows a linear istribution when t
广义分形维数是根据Ma et al.(1992)出版的1900-1990年期间中国大陆南北地震带发生的M≥6级地震和Press and Allen(1995)编写的1915-1994年期间美国南加州发生的M≥5.5级地震两份完整的地震目录进行的。Cq对t的对数-对数图，其中Cq(t)是广义相关积分，t是两个事件之间的年间隔时间，在正q处，当t
{"title":"Multifractal Measures of Time Series of Earthquakes","authors":"Jeen‐Hwa Wang, Chung-Wein Lee","doi":"10.4294/JPE1952.45.331","DOIUrl":"https://doi.org/10.4294/JPE1952.45.331","url":null,"abstract":"The generalized fractal dimensions are measured for the time series based on two complete earthquake catalogues: one with M≥6 earthquakes occurring in the north-south seismic belt of mainland China during the 1900-1990 period published by Ma et al. (1992) and the other with M≥5.5 earthquakes occurring in southern California, USA during the 1915-1994 period compiled by Press and Allen (1995). The log-log plot of Cq versus t, where Cq(t) is the generalized correlation integral and t is the interoccurrence time in years between two events, at positive q shows a linear istribution when t<tc. Dq is the slope of this linear portion. The value of tc decreases from 50.1 to 39.8 years for Chinese earthquakes and from 50.1 to 31.6 years for southern California events as q is increased from 0 to 15. For M≥6 Chinese earthquakes, the well-distributed, monotonically decreasing function of Dq, with increasing q would imply that such earthquakes have formed a multifractal time series. In contrast, the M≥5.5 southern California earthquakes might have not yet formed a complete multifractal time series or the number of these events is too small to accurately estimate the multifractal dimensions, especially for large qs. Different degrees of complexity of fault distributions in the two seismic regions might also be a factor in causing the difference in the Dq-q relations. In addition, the results also suggest that a Dq-q relation is better than the first three commonly-used values of Dq to completely represent a multifractal time series.","PeriodicalId":157777,"journal":{"name":"Journal of physics of the earth","volume":"159 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"1997-10-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"126907778","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
A two-dimensional reflection/transmission problem for SH-waves at a corrugated interface between homogeneous transversely isotropic half-spaces is considered. Rayleigh's method is adopted and expressions for reflection and transmission coefficients are obtained in closed form for the first-order approximation of the corrugation. Numerical computations for a particular model have been performed.
{"title":"Reflection and Refraction of SH-Waves at a Corrugated Interface between Two-Dimensional Transversely Isotropic Half-Spaces","authors":"S. K. Tomar, S. L. Saini","doi":"10.4294/JPE1952.45.347","DOIUrl":"https://doi.org/10.4294/JPE1952.45.347","url":null,"abstract":"A two-dimensional reflection/transmission problem for SH-waves at a corrugated interface between homogeneous transversely isotropic half-spaces is considered. Rayleigh's method is adopted and expressions for reflection and transmission coefficients are obtained in closed form for the first-order approximation of the corrugation. Numerical computations for a particular model have been performed.","PeriodicalId":157777,"journal":{"name":"Journal of physics of the earth","volume":"10 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"1997-10-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"133673164","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
A new time-series analysis called "wavelet transform" is applied to measure the group velocity of surface waves as compared with that obtained by the conventional Fourier transform. We use vertical-component Rayleigh waves for both synthetic seismograms and GDSN long-period data of oceanic paths. The results of this study are summarized as follows: for synthetic seismograms, moving-window analysis using the Fourier transform can measure the group velocity of the fundamental mode correctly, while the group velocity of the first-higher mode is systematically larger than the correct value. In contrast, the wavelet transform measures the group velocity of both modes precisely although the resolution in frequency may not be sufficiently high. For GDSN data propagating along the Pacific Ocean, both methods provide stable results for the group velocity of the fundamental mode in the period range of 20 to 100 s. Using the Fourier transform, we obtain the group velocities of the first-higher mode between 20 and 40 s although these values seem unreliable. In contrast, the wavelet transform can measure both modes precisely in the period range of 20 to 100 s for non-shallow events and even for shallow events with relatively small noise in the data. Another advantage of the wavelet analysis is that we can specify resolving power in group velocity measurement rigorously.
{"title":"Group Velocity Measurement of Surface Waves by the Wavelet Transform","authors":"T. Yamada, K. Yomogida","doi":"10.4294/JPE1952.45.313","DOIUrl":"https://doi.org/10.4294/JPE1952.45.313","url":null,"abstract":"A new time-series analysis called \"wavelet transform\" is applied to measure the group velocity of surface waves as compared with that obtained by the conventional Fourier transform. We use vertical-component Rayleigh waves for both synthetic seismograms and GDSN long-period data of oceanic paths. The results of this study are summarized as follows: for synthetic seismograms, moving-window analysis using the Fourier transform can measure the group velocity of the fundamental mode correctly, while the group velocity of the first-higher mode is systematically larger than the correct value. In contrast, the wavelet transform measures the group velocity of both modes precisely although the resolution in frequency may not be sufficiently high. For GDSN data propagating along the Pacific Ocean, both methods provide stable results for the group velocity of the fundamental mode in the period range of 20 to 100 s. Using the Fourier transform, we obtain the group velocities of the first-higher mode between 20 and 40 s although these values seem unreliable. In contrast, the wavelet transform can measure both modes precisely in the period range of 20 to 100 s for non-shallow events and even for shallow events with relatively small noise in the data. Another advantage of the wavelet analysis is that we can specify resolving power in group velocity measurement rigorously.","PeriodicalId":157777,"journal":{"name":"Journal of physics of the earth","volume":"23 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"1997-10-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"129052882","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
A one-dimensional BK dynamical lattice model (Burridge and Knopoff, 1967) is applied to simulate earthquakes for the study of the scaling relation between frequency and rupture length of earthquakes. Velocity-dependent friction controls the motion of mass elements. The distribution of the breaking strengths (i.e., static friction) is considered to be a fractal function. Simulation results show that the fractal dimension of the distribution of the breaking strengths is a minor factor in affecting the scaling of frequency versus rupture length. A fast velocity-weakening process from static friction to dynamic friction and a slow velocity-hardening one from dynamic friction to static friction are appropriate for interpreting the scaling of the frequency-rupture length (FL) relation. The frictional drop rather than the level of the breaking strength affects the FL scaling. Hence, the friction drop ratio (g) which determines the minimum value of the dynamic frictional force, is an important factor in influencing the FL relation. Smaller g (which a large friction drop) leads to a smaller scaling exponent value in the regime of localized events than larger g (with a smaller friction drop). The stiffness ratio, which is defined as the ratio of the stiffness of the coil spring to that of the leaf spring of the model, is also a significant parameter affecting the FL distribution. Nevertheless, simulation results show that small s is unable to produce a ower-law FL relation.
采用一维BK动力点阵模型(Burridge and Knopoff, 1967)模拟地震，研究地震频率与破裂长度的标度关系。速度相关的摩擦控制着质量要素的运动。断裂强度(即静摩擦)的分布被认为是分形函数。模拟结果表明，断裂强度分布的分形维数是影响频率随断裂长度变化的次要因素。从静摩擦到动摩擦的快速弱化过程和从动摩擦到静摩擦的缓慢硬化过程适合解释频率-断裂长度(FL)关系的标度。影响FL结垢的是摩擦降而不是断裂强度水平。因此，决定动摩擦力最小值的摩擦降比(g)是影响FL关系的重要因素。较小的g(摩擦降较大)在局部事件中比较大的g(摩擦降较小)导致较小的标度指数值。刚度比定义为模型中螺旋弹簧与钢板弹簧的刚度之比，也是影响FL分布的重要参数。然而，仿真结果表明，小s不能产生低律FL关系。
{"title":"On the Frequency Distribution of Rupture Lengths of Earthquakes Synthesized from a One-Dimensional Dynamical Lattice Model.","authors":"Jeen‐Hwa Wang","doi":"10.4294/JPE1952.45.363","DOIUrl":"https://doi.org/10.4294/JPE1952.45.363","url":null,"abstract":"A one-dimensional BK dynamical lattice model (Burridge and Knopoff, 1967) is applied to simulate earthquakes for the study of the scaling relation between frequency and rupture length of earthquakes. Velocity-dependent friction controls the motion of mass elements. The distribution of the breaking strengths (i.e., static friction) is considered to be a fractal function. Simulation results show that the fractal dimension of the distribution of the breaking strengths is a minor factor in affecting the scaling of frequency versus rupture length. A fast velocity-weakening process from static friction to dynamic friction and a slow velocity-hardening one from dynamic friction to static friction are appropriate for interpreting the scaling of the frequency-rupture length (FL) relation. The frictional drop rather than the level of the breaking strength affects the FL scaling. Hence, the friction drop ratio (g) which determines the minimum value of the dynamic frictional force, is an important factor in influencing the FL relation. Smaller g (which a large friction drop) leads to a smaller scaling exponent value in the regime of localized events than larger g (with a smaller friction drop). The stiffness ratio, which is defined as the ratio of the stiffness of the coil spring to that of the leaf spring of the model, is also a significant parameter affecting the FL distribution. Nevertheless, simulation results show that small s is unable to produce a ower-law FL relation.","PeriodicalId":157777,"journal":{"name":"Journal of physics of the earth","volume":"171 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"1997-10-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"134187847","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
We select the earthquakes that satisfy the following conditions: 1) epicenters are located in the areas AA' and BB' in Figs. 1 to 3, 2) magnitude •†2.5, and 3) depth •†35 km. No northern limit is applied to the data in the Chugoku region. The southern limit in the selection of the earthquakes in the Seto Inland Sea and Shikoku region is not rigid. The limit is a latitude of about 34•‹N. However, the aim of this study is to determine the northern end of the subcrustal earthquakes in the Chugoku region, and the ambiguity of the southern limit has no effect on the conclusion of this study.
{"title":"Subcrustal seismicity beneath the Southern Part of the Chugoku Region, Japan","authors":"Y. Kinoshita, I. Nakanishi","doi":"10.4294/JPE1952.45.307","DOIUrl":"https://doi.org/10.4294/JPE1952.45.307","url":null,"abstract":"We select the earthquakes that satisfy the following conditions: 1) epicenters are located in the areas AA' and BB' in Figs. 1 to 3, 2) magnitude •†2.5, and 3) depth •†35 km. No northern limit is applied to the data in the Chugoku region. The southern limit in the selection of the earthquakes in the Seto Inland Sea and Shikoku region is not rigid. The limit is a latitude of about 34•‹N. However, the aim of this study is to determine the northern end of the subcrustal earthquakes in the Chugoku region, and the ambiguity of the southern limit has no effect on the conclusion of this study.","PeriodicalId":157777,"journal":{"name":"Journal of physics of the earth","volume":"68 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"1997-08-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"115683246","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
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