Discontinuity of the Mozumi–Sukenobu fault low-velocity zone, central Japan, inferred from 3-D finite-difference simulation of fault zone waves excited by explosive sources

Mamada, Yutaka; Kuwahara, Yasuto; Ito, Hisao; Takenaka, Hiroshi

doi:10.1016/j.tecto.2003.09.008

Cited by 14 publications

(17 citation statements)

References 24 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…In the last 20 years various studies used FZ trapped waves to characterize the internal structure of large fault and earthquake rupture zones (e.g. Li & Leary 1990; Li et al 1994; Rovelli et al 2002; Ben‐Zion et al 2003; Haberland et al 2003; Mamada et al 2004; Wang et al 2009). The presence of trapped waves implies a uniform or smoothly varying continuous tabular zone of damage in a region between the recording stations and the generating events (e.g.…”

Section: Discussionmentioning

confidence: 99%

Diversity of fault zone damage and trapping structures in the Parkfield section of the San Andreas Fault from comprehensive analysis of near fault seismograms

Lewis¹,

Ben‐Zion²

2010

Geophysical Journal International

113

View full text Add to dashboard Cite

S U M M A R YWe perform comprehensive analyses of trapped waves and signals of damaged fault zone rocks associated with time delays of body waves along the Parkfield section of the San Andreas Fault (SAF). Waveforms generated by thousands of earthquakes and recorded by near fault stations in several permanent and temporary deployments are examined, with attention to the possible influence of a lithology contrast across the fault on signals of the low velocity damage zone. Clear candidate trapped waves are identified at only three stations, MMNB and two of the other near fault stations (FLIP and PIES) further to the NW. Clear candidate trapped waves are not seen at any of the near fault stations to the SE of MMNB. The locations of the events generating good candidate trapped waves at MMNB and the other two stations are not distributed broadly in space, but clustered in a small number of locations. Moreover, events that generate clear candidate trapped waves at one station do not typically generate trapped waves at the other two stations. These observations imply that the damage zone is highly variable along strike and that a coherent connected waveguide does not exist for distances along strike larger than at most 3-5 km (the distance between stations). Synthetic waveform fits for observed trapped waves at stations MMNB and FLIP indicate that the most likely parameters of the trapping structures at these locations are widths of about 150 m, depths of about 3 km, velocity reductions of 30-40 per cent, and Q values of 10-40. Synthetic calculations of trapped waves demonstrate that if there is a contrast of seismic velocity across the fault, the trapped waves are delayed relative to the S wave arrival. Trapped waves at station MMNB, and to a lesser extent also at stations FLIP and PIES in the NW section, show this characteristic. This suggests a lithology contrast in the top few km at these locations, in agreement with results from tomography and studies of head waves in the Parkfield area. At several mini across-fault arrays, where trapped waves are not observed, a low velocity damage zone is detected from the delay in the arrival time of body wave phases relative to a nearby off-fault station. The observed delay of the S wave is greater than the P wave delay, consistent with the existence of a damage zone with Poisson ratio of about 0.33. The observations of time delays without trapped waves indicate that parts of the damage zone are insufficiently coherent to generate trapped waves. A broader damage zone may exist in the region between the SAF and the South West Fracture Zone. The results highlight the diversity of damage structures along the ∼40 km of the SAF examined in this study, and imply that fault imaging based on data at single sites does not necessarily apply to a larger section.

show abstract

Section: Discussionmentioning

confidence: 99%

Diversity of fault zone damage and trapping structures in the Parkfield section of the San Andreas Fault from comprehensive analysis of near fault seismograms

Lewis¹,

Ben‐Zion²

2010

Geophysical Journal International

113

View full text Add to dashboard Cite

show abstract

“…However, the observations of FZ trapped waves due to sources well outside the fault imply that the trapping structures are overall limited to the stable (velocity strengthening) uppermost portion of the crust that is above the seismicity and largely mechanically passive. Shallow trapping structures were also found for faults in central Italy (Rovelli et al 2002) and central Japan (Mamada et al 2004). The results imply that FZ trapped waves are generally not useful for in situ characterization of FZ structure in the depth range where earthquakes nucleate and the majority of co‐seismic slip occurs (3–15 km).…”

Section: Introductionmentioning

confidence: 93%

High-resolution imaging of the Bear Valley section of the San Andreas fault at seismogenic depths with fault-zone head waves and relocated seismicity

McGuire

Ben‐Zion

2005

Geophysical Journal International

View full text Add to dashboard Cite

S U M M A R YDetailed imaging of fault-zone (FZ) material properties at seismogenic depths is a difficult seismological problem owing to the short length scales of the structural features. Seismic energy trapped within a low-velocity damage zone has been utilized to image the fault core at shallow depths, but these phases appear to lack sensitivity to structure in the depth range where earthquakes nucleate. Major faults that juxtapose rocks of significantly different elastic properties generate a related phase termed a fault-zone head wave (FZHW) that spends the majority of its path refracting along the fault. We utilize data from a dense temporary array of seismometers in the Bear Valley region of the San Andreas Fault to demonstrate that head waves have sensitivity to FZ structure throughout the seismogenic zone. Measured differential arrival times between the head waves and direct P arrivals and waveform modelling of these phases provide high-resolution information on the velocity contrast across the fault. The obtained values document along-strike, fault-normal, and downdip variations in the strength of the velocity contrast, ranging from 20 to 50 per cent depending on the regions being averaged by the ray paths. The complexity of the FZ waveforms increases dramatically in a region of the fault that has two active strands producing two separate bands of seismicity. Synthetic waveform calculations indicate that geological observations of the thickness and rock-type of the layer between the two strands are valid also for the subsurface structure of the fault. The results show that joint analysis of FZHWs and direct P arrivals can resolve important smallscale elements of the FZ structure at seismogenic depths. Detailed characterization of material contrasts across faults and their relation to earthquake ruptures is necessary for evaluating theoretical predictions of the effects that these structures have on rupture propagation.

show abstract

“…In addition, seismic velocity values are decreased across the Mozumi fault relative to the wall rock (Table 5 and Figure 9). The average P wave and S wave velocities determined from the seismic studies for protolith are 4.6–4.9 km/s and ∼2.6–3.0 km/s, respectively [ Mamada et al , 2004; Mizuno et al , 2004]. Four types of fault zone structures are recognized, including fractures along borehole A (Figure 6), lithology changes, including clay composition, foliation and other microstructures, and heterogeneity of physical and mechanical properties [ Forster et al , 2003; this study].…”

Section: Discussionmentioning

confidence: 99%

“…Rock samples from drilled core associated with the Active Fault Survey Tunnel (AFST) and continuous borehole geophysical logs are combined with data on porosity and permeability to document the variations in fault zone properties across the fault. We discuss the results in light of a recent study of inversion of fault zone waves in the Mozumi fault [ Mamada et al , 2004; Mizuno et al , 2004] and in situ hydraulic tests [ Nohara et al , 2006] to document the relationship between deformation mechanisms, alteration, and elastic properties of the fault zone. This work provides data on the in situ chemical, physical, and mechanical properties of the internal portion of an active fault in clastic sedimentary rocks in the upper portion of the crust, but at depths where weathering has not disturbed the textures and structures associated with faulting and fluid flow.…”

Section: Introductionmentioning

confidence: 99%

Composition, microstructures, and petrophysics of the Mozumi fault, Japan: In situ analyses of fault zone properties and structure in sedimentary rocks from shallow crustal levels

et al. 2008

View full text Add to dashboard Cite

[1] We characterize the chemical, microstructural, and geophysical properties of faultrelated rock samples from the 80-100 m wide Mozumi fault zone, north central Honshu, Japan. The fault is exposed in a research tunnel 300-400 m below the ground, and we combine geological data with borehole geophysical logs to determine the elastic and seismic properties of the fault zone. Detailed mapping within the tunnel reveals that the fault zone consists of two zones of breccia to foliated cataclasites 20 and 50 m thick. Two narrow (tens of centimeters wide) principal slip zones on which most of the slip occurred bound the central fault zone. The dominant deformation mechanisms within the fault zone were brittle fracture, brecciation, slip localization, plastic deformation, and vein formation in a sericite-calcite rich matrix. Clay alteration patterns are complex within the fault zone, with clay-rich fault breccia enriched in smectite, illite, and kaolinite relative to the kaolinite and illite dominant in the host rock. Whole rock geochemical analyses show that the fault-related rocks are depleted in Fe, Na, K, Al, Mg, and Si relative to the host rock. Poisson's ratio correspond to fault breccia with increased porosity, high fluid content, and low resistivity values. Taken together, these data show that the shallow portion of the Mozumi fault consists of a complex zone of anastomosing narrow slip zones that bound broad zones of damage. Fluid-rock alteration and deformation created altered fault-related rocks, which have resulted in overall reduced interval velocities of the fault zone. These data indicate that seismic waves traveling along the interface or internally reflected in the fault zone would encounter rocks of differing and reduced elastic properties relative to the host rocks but that in detail, material properties within the fault may vary.Citation: Isaacs, A. J., J. P. Evans, P. T. Kolesar, and T. Nohara (2008), Composition, microstructures, and petrophysics of the Mozumi fault, Japan: In situ analyses of fault zone properties and structure in sedimentary rocks from shallow crustal levels,

show abstract

Discontinuity of the Mozumi–Sukenobu fault low-velocity zone, central Japan, inferred from 3-D finite-difference simulation of fault zone waves excited by explosive sources

Cited by 14 publications

References 24 publications

Diversity of fault zone damage and trapping structures in the Parkfield section of the San Andreas Fault from comprehensive analysis of near fault seismograms

Diversity of fault zone damage and trapping structures in the Parkfield section of the San Andreas Fault from comprehensive analysis of near fault seismograms

High-resolution imaging of the Bear Valley section of the San Andreas fault at seismogenic depths with fault-zone head waves and relocated seismicity

Composition, microstructures, and petrophysics of the Mozumi fault, Japan: In situ analyses of fault zone properties and structure in sedimentary rocks from shallow crustal levels

Contact Info

Product

Resources

About