reverse and normal drag along a fault an analysis of the theoretical displacement field around a single dip slip fault at depth reveals that normal and reverse fault drag develop by perturbation flow induced by fault slip we analytically model the heterogeneous part of the instantaneous displacement field of an isolated two dimensional mode ii fault in an infinite homogeneous elastic body in response to fault slip material on both sides of the fault is displaced and opposing circulation cells arise on opposite sides of the fault with displacement magnitudes increasing towards the center of the fault both normal and reverse drag can develop at the fault center depending on the angle between the markers and the fault normal drag develops there for low angles 30 408 and reverse drag for higher angles a comparison of the theoretical results with published models and natural examples reveals that the characteristics of normal and reverse fault drag are largely insensitive to the scale and rheology of the faulted rocks and that drag forces generated by frictional resistance need not be the primary cause of fault drag fault drag has some interesting geometric implications for normal and reverse fault terminology emphasizing the importance for discrimination of vertical separation and throw furthermore our results lead us to propose an alternative model for the formation of rollover anticlines above normal faults

late pliocene and quaternary glaciations of new zealand abstract evidence of late pliocene glaciations is fragmentary the ross glaciation in northwest south island is correlated with the first marine faunal evidence of marked cooling in the wanganui basin in southern north island it is inferred to be in the 2 6 2 4 ma age range the porika glaciation in a separate area of northwest south island is younger judged by palynology and is correlated with a cooling 2 2 2 1 ma bp inferred from stratigraphic evidence of lowered sea level in the wanganui basin a gap of 1 5 ma in the record of glaciations is largely filled by wanganui basin marine sediments although an unconformity cuts out the record between ca 1 45 and 1 0 ma bp since then the many sedimentary cycles caused by sea level changes are presumed to be glacio eustatic in origin uplifted interglacial marine terraces back to marine oxygen isotope stage 17 and river terraces formed by cold climate aggradation are linked into the cyclic sequence through loess and tephra in their cover beds east of the south island cores from the dsdp site 594 in the southwest pacific record the earliest glaciation and higher in the core nine periods of south island glaciation in the last 0 7 ma onshore because of uplift and erosion only the last four glaciations assigned to oxygen isotope stages 10 8 6 and 4 2 are identified being named nemona waimaunga waimea and otira glaciations they are best known in north westland northwest south island where the relations of glacial outwash and interglacial shoreline deposits are displayed the late otira glaciation stage 2 is radiocarbon dated as beginning somewhat before 22 3 ka bp culminating ca 18 ka bp and ending at ca 14 ka bp when rapid deglaciation began a relatively small advance at ca 12 ka bp may have been followed by little change until after 8 6 ka bp recession was then followed by a period of advance from ca 5 ka bp until recent centuries and a subsequent recession that still continues

the application of reflection seismology to the investigation of the geometry of near surface units and faults in the blake river group abitibi belt quebec reprocessing of part of a lithoprobe high resolution seismic reflection line across the southern part of the abitibi belt has improved the imaging of shallow reflections and allowed correlation of the data with surface geology enhancement of early reflections was accomplished by focusing on the high frequency content of the data this improved resolution of reflections at two way traveltime as early as 0 3 s and attenuated noise such as shear waves the shallow reflections are interpreted as impedance contrasts at the contact between a metadiabase diorite body and metavolcanics rocks offsets of the reflectors correlate with faults mapped at the surface and indicate a downdropped block which may be of interest for mineral exploration

geomorphic constraints on listric thrust faulting implications for active deformation in the mackenzie basin south island new zealand 1 deformed fluvial terraces preserved over active thrust related folds record the kinematics of folding as fault slip accumulates on the underlying thrust in the mackenzie basin of southern new zealand the kinematics revealed by folded fluvial terraces along the active ostler and irishman creek fault zones are inconsistent with traditional models for thrust related folding in which spatially uniform rock uplift typically occurs over planar fault ramps instead warped and tilted terraces in the mackenzie are characterized by broad continuous backlimbs and abrupt forelimbs and suggest folding through progressive limb rotation by relating this pattern of surface deformation to the underlying thrust with a newly developed simple geometric and kinematic model we interpret both faults as listric thrusts rooted at depth into gently dipping planar fault ramps constraints on the model from detailed topographic surveying of deformed terraces ground penetrating radar over active fault scarps and luminescence dating of terrace surfaces suggest slip rates for the ostler and irishman creek faults of 1 1 1 7 mm yr and 0 5 0 7 mm yr respectively the predicted depth of listric faulting for the ostler fault 0 7 0 2 0 1 km and the irishman creek fault 1 3 0 5 0 1 km generally agrees with geophysical estimates of basin depth in the mackenzie and suggests control of preexisting basin architecture on the geometry of active thrusting despite the potential effects of changes in fault curvature and hanging wall internal deformation the methodology presented here provides a simple tool for approximating the kinematics of surface deformation associated with slip along listric or curviplanar thrust faults

shallow seismic reflection study of a glaciated valley shallow seismic reflection data were recorded along two long 1 6 km intersecting profiles in the glaciated suhre valley of northern switzerland appropriate choice of source and receiver parameters resulted in a high fold 36 48 data set with common midpoints every 1 25 m as for many shallow seismic reflection data sets upper portions of the shot gathers were contaminated with high amplitude source generated noise e g direct refracted guided surface and airwaves spectral balancing was effective in significantly increasing the strength of the reflected signals relative to the source generated noise and application of carefully selected top mutes ensured guided phases were not misprocessed and misinterpreted as reflections resultant processed sections were characterized by distributions of distinct seismic reflection patterns or facies that were bounded by quasi continuous reflection zones the uppermost reflection zone at 20 to 50 ms 15 to 40 m depth originated from a boundary between

effects of near surface waveguides on shallow high resolution seismic refraction and reflection data waveguides formed between the earth s free surface and sharp subsurface velocity discontinuities such as the watertable may have a significant impact on high resolution seismic refraction and reflection data energy trapped in such waveguides may propagate over long distances with little loss due to geometrical spreading the dispersive nature of the guided waves results in pronounced shingling of the first arrivals this narrows the optimum reflection window between the first arrivals and the ground roll and may lead to mispicking of first breaks and difficulties in identifying and processing shallow reflections

computation of refraction static corrections using first break traveltime differences differences in first arrival traveltimes between adjacent records in multifold reflection surveys can be used to compute the depth and velocity structure of near surface layers the procedure uses the redundancy of first break data in multifold surveys to enable a statistically reliable refraction analysis to be undertaken for either end on or split spread recording geometries the traveltime differences as a function of source receiver offset provide a direct indication of the number of refractors present with each refractor being defined by an offset range with a constant time difference for each refractor the time difference value at a common receiver from two shotpoints is used to partition the intercept time into the delay time at each shotpoint this procedure is repeated until the delay times at all shotpoints and for all refractors have been computed refractor depths and velocities are evaluated from this suite of delay times a surface consistent static correction to a selected datum level is then calculated at each surface station using a replacement velocity equal to that of the deepest refractor in a case history from the canadian rocky mountain foothills short and intermediate wavelength weathering static anomalies were resolved successfully elevation and weathering static corrections of up to 40 ms were computed with an estimated error of less than or 3 ms

pbzn mineralization associated with diapirism fluid inclusion and stable isotope h c o evidence for the origin and evolution of the fluids at fedj el adoum tunisia pb zn mineralizations occur in the contact zone to a saliferous diapir and its surrounding cretaceous limestonerich sediments the diapir of triassic formations was initially intruded hot from a depth of 3 7 km during the cretaceous three principal types of mineralization occur bedded vein and massive combined microthermometric and stable isotope h c o studies have characterized three principal thermal events before cool meteoric waters entered the system 1 1 hot 170 250 c saline 22 33 eq wt nacl fluids of probable deep formation water origin with d 43 and 18o 20 precipitated calcite with 13c 8 and celestite in the inner part of the contact zone with the diapir 2 2 hot 100 130 c saline 18 23 eq wt nacl fluids with d 60 and 18o 13 containing co2 n2 and hydrocarbons precipitated sphalerite calcite 13c 9 quartz and minor galena as banded mineralization in the outer part of the contact zone more galena rich vein mineralizations in the contact zone were deposited at similar temperatures from comparable fluids mineralizing solutions are interpreted to be formation waters with the carbonate carbon being derived from organic carbon the colloform textures in the banded mineralization suggest that the nearby sedimentary basin underwent episodic dewatering 3 3 warm 70 90 c saline 16 22 eq wt nacl fluids with d 110 and 18o 10 precipitated calcite with 13c 16 galena rich ore in the massive mineralizations and vein mineralizations in the cenomanian turonian limestones and essentially sulphide free calcite in the banded and contact vein mineralizations a locally derived organic water origin is proposed where both hydrogen and carbon were derived from organic constituents such as petroleum during bacterial sulphate reduction reactions variable d and salinity values suggest mixing processes between the d depleted organic water and a more d rich formation or meteoric water 4 4 low temperature 50 c meteoric waters with d 15 to 25 introduced a second generation of calcite with the carbonate largely coming from the sedimentary carbonates in the massive and turonian vein mineralizations anhydrite was probably converted to gypsum at about this time and before fedj el adoum arrived at its present altitude

ultrahigh resolution seismic reflection imaging of the alpine fault new zealand 1 high resolution seismic reflection surveys across active fault zones are capable of supplying key structural information required for assessments of seismic hazard and risk we have recorded a 360 m long ultrahigh resolution seismic reflection profile across the alpine fault in new zealand the alpine fault a continental transform that juxtaposes major tectonic plates is capable of generating large m 7 8 damaging earthquakes our seismic profile across a northern section of the fault targets fault zone structures in holocene to late pleistocene sediments and underlying triassic and paleozoic basement units from 3 5 to 150 m depth since ultrashallow seismic data are strongly influenced by near surface heterogeneity and source generated noise an innovative processing sequence and nonstandard processing parameters are required to produce detailed information on the complex alluvial glaciofluvial and glaciolacustrine sediments and shallow to steep dipping fault related features we present high quality images of structures and deformation within the fault zone that extend and complement interpretations based on shallow paleoseismic and ground penetrating radar studies our images demonstrate that the alpine fault dips 75 80 to the southeast through the quaternary sediments and there is evidence that it continues to dip steeply between the shallow basement units we interpret characteristic curved basement surfaces on either side of the alpine fault and deformation in the footwall as consequences of normal drag generated by the reverse slip components of displacement on the fault the fault dip and apparent 35 m vertical offset of the late pleistocene erosional basement surface across the alpine fault yield a provisional dip slip rate of 2 0 0 6 mm yr the more significant dextral slip rate cannot be determined from our seismic profile

quaternary slip rate and geomorphology of the alpine fault implications for kinematics and seismic hazard in southwest new zealand glacial landforms at 12 localities in 9 river valleys are offset by the southern end of the onshore alpine fault offsets cluster at 435 1240 and 1850 m consistent with evidence for glacial retreat at 18 58 and 79 calendar ka the peak of an offset fluvial aggradation surface is correlated with the last glacial maximum at 22 ka displacement rates derived from features aged 18 22 58 and 79 cal ka are 24 2 2 2 23 2 4 9 21 4 2 6 and 23 5 2 7 mm yr respectively with uncertainties at the 95 confidence level the joint probability weighted mean and arithmetic mean of all observations pooled by rank are 23 1 1 5 23 2 1 4 and 23 1 1 7 mm yr respectively we conclude that the mean surface displacement rate for this section of the alpine fault is 23 1 mm yr with standard error in the range of 0 7 0 9 mm yr the reduction in estimated long term slip rate from 26 6 mm yr to 23 2 mm yr results in an increase in estimated hazard associated with faulting distributed across the rest of the plate boundary model dependent probabilities of alpine fault rupture within the next 50 yr are in the range 14 29 the 36 3 mm yr of total plate motion nuvel 1a is partitioned into 23 2 mm yr of alpine fault dextral strike slip 12 4 mm yr of horizontal motion by clockwise block rotations and oblique dextral reverse faulting up to 80 km southeast of the alpine fault and 5 3 mm yr of heave on reverse faults at the peripheries of the plate boundary

seismic exploration of continental strike slip zones abstract seismic exploration of both palaeozoic and active strike slip zones shows strike slip faults that penetrate all or most of the crust offsets on the moho are evident particularly at young and active zones with a component of compression such as the alpine fault of new zealand where a change in crustal thickness of about 20 km is observed moho offsets for the old palaeozoic strike slip zones are usually much less prominent careful migration of crustal seismic reflection data from some of these zones shows that instead of sharp offsets the moho structure consists of a localized keel type crustal thickening of a few kilometres in amplitude and occurs over a zone approximately 10 km wide the large moho offsets of young strike slip zones may in some cases partially decay with time active strike slip zones are becoming an important focus of study but seismic exploration is hampered by complex near surface geology 3d structure and the difficulty of imaging steeply dipping structure in the subsurface in order to meet this challenge a wide range of seismic techniques is now being deployed these include wide angle seismic reflection refraction p wave delays and the study of guided s waves results from california give geophysical images of vertical strike slip faults that penetrate to the moho in contrast the alpine fault of new zealand appears to be a surface manifestation of an inclined 40 ramp extending down to the lower crust and along which uplift and exhumation of the continental crust and possibly strike slip motion is taking place

origin of small scale segmentation and transpressional thrusting along the alpine fault new zealand the alpine fault is the major structural feature of the australian pacific plate boundary in the south island of new zealand geologic evidence suggests that half to three quarters of the plate boundary displacement is accommodated by movement on the fault detailed investigation of the central section of the alpine fault has revealed that it consists of oblique thrust sections striking 020 050 that are linked by subvertical right lateral faults striking between 065 and 090 the segmentation is on a scale of 1 10 km similarly oriented right lateral faults are abundant southeast of the alpine fault and are consistent with stresses induced in an elastic layer by an oblique slip ductile fault zone below propagation of the fault to the surface is predicted to result in an en echelon arrangement of strike slip and thrust segments it is suggested that the spatial distribution of segments is affected by the existence of deeply incised valleys in the hanging wall that disturb the stress field to depths of 1 4 km the segmentation is near surface and does not appear to act as a barrier to the propagation of large earthquakes

a simple efficient method of dip moveout correction1 abstract much of the success of modern seismic data processing derives from the use of the stacking process unfortunately as is well known conventional normal moveout correction nmo introduces mispositioning of data and hence mis stacking when dip is present dip moveout correction dmo is a technique that converts non zero offset seismic data after nmo to true zero offset locations and reflection times irrespective of dip the combination of nmo and dmo followed by post stack time migration is equivalent to but can be implemented much more efficiently than full time migration before stack in this paper we consider the frequency wavenumber dmo algorithm developed by hale our analysis centres on the result that for a given dip the combination of nmo at migration velocity and dmo is equivalent to nmo at the appropriate dip dependent stacking velocity this perspective on dmo leads to computationally efficient methods for applying hale dmo and also provides interesting insights on the nature of both dmo and conventional stacking

multiscale seismic imaging of active fault zones for hazard assessment a case study of the santa monica fault zone los angeles california high resolution seismic reflection profiles at two different scales were acquired across the transpressional santa monica fault of north los angeles as part of an integrated hazard assessment of the fault the seismic data confirm the location of the fault and related shallow faulting seen in a trench to deeper structures known from regional studies the trench shows a series of near vertical strike slip faults beneath a topographic scarp inferred to be caused by thrusting on the santa monica fault analysis of the disruption of soil horizons in the trench indicates multiple earthquakes have occurred on these strike slip faults within the past 50 000 years with the latest being 1000 to 3000 years ago a 3 8 km long high resolution seismic reflection profile shows reflector truncations that constrain the shallow portion of the santa monica fault upper 300 m to dip northward between 30 and 55 most likely 30 to 35 in contrast to the 60 to 70 dip interpreted for the deeper portion of the fault pr

combining seismic reflection with multifold wide aperture profiling an effective strategy for high resolution shallow imaging of active faults 1 shallow imaging of fault zones is a challenging task we investigate if this issue can be successfully addressed by combining reflection seismics with non standard multifold wide aperture profiling a strategy pertaining to crustal scale exploration so far near offset reflection and multifold wide aperture data are simultaneously recorded along two profiles in a small basin crossed by an active fault in southern italy imaging consists of multiscale seismic tomography complemented by cdp processing of near offset reflections and of data spanning a large offset range by combining smooth vp and reflectivity images we pinpoint the fault location and yield a valuable picture of the basin performance of each exploration technique strongly varies in the two surveys depending on the local geology thus the combined exploration strategy not only yields complementary images for enhanced interpretation but also allows extending the range of applicability of shallow seismics for fault detection reducing the risk of unsuccessful investigations

visualization of active faults using geometric attributes of 3d gpr data an example from the alpine fault zone new zealand three dimensional ground penetrating radar gpr data are routinely acquired for diverse geologic hydrogeologic archeological and civil engineering purposes interpretations of these dataareinvariablybasedonsubjectiveanalysesofreflectionpatterns such analyses are heavily dependent on interpreter expertiseandexperience usingdataacquiredacrossgravelunitsoverlyingthealpinefaultzoneinnewzealand wedemonstratethe utilityofvariousgeometricattributesinreducingthesubjectivity of3dgprdataanalysis weuseacoherence basedtechniqueto compute the coherency azimuth and dip attributes and a graylevel co occurrence matrixglcmmethod to compute the texture basedenergy entropy homogeneity andcontrastattributes a selection of the gpr attribute volumes allows us to highlight key aspects of the fault zone and observe important features not apparent in the standard images this selection also provides information that improves our understanding of gravel deposition andtectonicstructuresatthestudysite anewdepositional structuralmodellargelybasedontheresultsofouranalysisofgprattributes includes four distinct gravel units deposited in three phases and a well defined fault trace this fault trace coincides with a zone of stratal disruption and shearing bound on one side by upward tilted to synclinally folded stratified gravels and on the other side by moderately dipping stratified alluvial fan gravelsthatcouldhavebeenaffectedbylateralfaultdrag whenused in tandem the coherence and texture based attribute volumes can significantly improve the efficiency and quality of 3d gpr interpretation especially for complex data collected across activefaultzones

late quaternary slip rates and slip partitioning on the alpine fault new zealand abstract published geological data on late quaternary offsets on the alpine fault new zealand have been assembled into a common format and analysed with respect to uncertainties uncertainties arise mainly from measurement of offset features relating apparent offsets to actual fault slip and dating the offset features despite the considerable uncertainties the data form a coherent set consistent with a relatively constant rate of strike slip of 27 5 mm year between milford sound and hokitika this rate represents 70 75 of the fault parallel interplate motion north of the confluence with the hope fault the rate drops substantially dip slip rates on the other hand show considerable variation along strike rising to a maximum of more than 10 mm year in the central section and decreasing to zero at the southern end partitioning of c 25 of the interplate slip on to structures east of the alpine fault occurs in the central section consistent with predictions from critical wedge models the partitioning of all the fault normal component of displacement on to other structures in the south may be related in part to a doubling in width of the deforming wedge to the east most probably however the fault normal displacement is mainly accommodated by underthrusting of the australian plate offshore due to a change in the nature of the crust from continental to oceanic

a workshop examination of shallow seismic reflection surveying in september 1996 the office of basic energy sciences of the u s department of energy doe sponsored a research workshop in berkeley california where approximately 20 participants analyzed the potential and limitations of near surface seismic reflection methods

seismic reflection images of shallow faulting northernmost mississippi embayment north of the new madrid seismic zone high resolution seismic reflection surveys document tectonic faults that displace pleistocene and older strata just beyond the northeast termination of the new madrid seismic zone at the northernmost extent of the mississippi embayment these faults which are part of the fluorspar area fault complex in southeastern illinois are directly in line with the northeast trending seismic zone the reflection data were acquired using an elastic weight drop source recorded to 500 msec by a 48 geophone array 24 fold with a 10 ft 3 0 m station interval recognizable reflections were recorded to about 200 msec 100 150 m the effects of multiple reflections numerous diffractions low apparent velocity i e steeply dipping noise and the relatively low frequency content of the recorded signal provided challenges for data processing and interpreting subtle fault offsets data processing steps that were critical to the detection of faults included residual statics post stack migration deconvolution and noise reduction filtering seismic migration was crucial for detecting and mitigating complex fault related diffraction patterns which produced an apparent folding of reflectors on unmigrated sections detected individual offsets of shallow reflectors range from 5 to 10 m for the top of paleozoic bedrock and younger strata the migrated sections generally indicate vertical to steeply dipping normal and reverse faults which in places outline small horsts and or grabens tilting or folding of stratal reflectors associated with faulting is also locally observed at one site the observed faulting is superimposed over a prominent antiformal structure which may itself be a product of the quaternary deformation that produced the steep normal and reverse faults our results suggest that faulting of the paleozoic bedrock and younger sediments of the northern mississippi embayment is more pervasive and less localized than previously thought

velocity and attenuation in partially saturated rocks poroelastic numerical experiments we use a poroelastic modelling algorithm to compute numerical experiments on wave propagation in a rock sample with partial saturation using realistic fluid distribution patterns from tomography scans frequencies are in the range 10 to 500 khz the rock is a homogeneous isotropic sandstone partially filled with gas and water which are defined by their characteristic values of viscosity compressibility and density we assume no mixing and that the two different pore fills occupy different macroscopic regions the von karman self similar correlation function is used employing different fractal parameters to model uniform and patchy fluid distributions respectively where effective saturation is varied in steps from full gas to full water saturation without resorting to additional matrix fluid interaction mechanisms we are able to reproduce the main features of the variation in wave velocity and attenuation with effective saturation and frequency as those of published laboratory experiments furthermore the behaviour of the attenuation peaks versus water saturation and frequency is similar to that of white s model the conversion of primary p wave energy into dissipating slow waves at the heterogeneities is shown to be the main mechanism for attenuating the primary wavefield fluid gas patches are shown to affect attenuation more than equivalent patches in the permeability or solid grain properties

variable crustal structure of strike slip fault zones as observed on deep seismic reflection profiles seismic reflection profiling across strike slip faults has revealed a distinct variation in deep crustal structure profiles across the san andreas great glen and bray faults depict a near vertical reflection free zone that appears to truncate and in some cases offset reflections interpreted to have originated from the base of the crust a near vertical crustal penetrating fault zone is suggested for these continental transform faults in contrast reflection profiles across intra plate strike slip fault systems such as the northern walker lane and garlock faults suggest that they are decoupled in the middle crust by subhorizontal detachments these detachments are inferred from reflections that are traceable below the surface faults without disruption such detachments in the middle crust may act to ease the rotation of upper crustal blocks adjacent to strike slip fault zones as observed in paleomagnetic studies furthermore moderately dipping reflections interpreted to be from the fault zone project to the surface traces of the northern walker lane faults and the frontal faults of the wichita uplift indicating that these strike slip faults with large components of dip slip displacement are not vertical but dip moderately into the mid crust although the available data sets are still few they suggest that there is a primary variation in fault geometry that is related to the different behavior of transform versus intra plate strike slip fault systems

refraction tomography over a buried waste disposal site determining the depth and geometry of a landfill s lower boundary is a difficult task potential field methods generally lack the necessary depth resolution and seismic reflection data are usually contaminated by source generated noise in the time range of interest 50 ms to address this problem we have developed a surface 2 d tomographic refraction scheme that is based on a fast finite difference eikonal solver and an inversion method that incorporates appropriate damping and smoothing constraints this new scheme has been applied to a first arrival traveltime data set collected across adjacent landfills in northern switzerland high quality seismic data were collected along five profiles that crossed the landfills and two that sampled undisturbed natural sediments seismic waves generated from multiple shots were recorded on large numbers of closely spaced receivers during quiet evening periods reliability of the resultant velocity tomograms was estimated on the basis of 1 ray diagrams 2 plot

steep dip seismic imaging of the shallow san andreas fault near parkfield seismic reflection and refraction images illuminate the san andreas fault to a depth of 1 kilometer the prestack depth migrated reflection image contains near vertical reflections aligned with the active fault trace the fault is vertical in the upper 0 5 kilometer then dips about 70 to the southwest to at least 1 kilometer subsurface this dip reconciles the difference between the computed locations of earthquakes and the surface fault trace the seismic velocity cross section shows strong lateral variations relatively low velocity 10 to 30 high electrical conductivity and low density indicate a 1 kilometer wide vertical wedge of porous sediment or fractured rock immediately southwest of the active fault trace

seismic measurements of the internal properties of fault zones the internal properties within and adjacent to fault zones are reviewed principally on the basis of laboratory borehole and seismic refraction and reflection data the deformation of rocks by faulting ranges from intragrain microcracking to severe alteration saturated microcracked and mildly fractured rocks do not exhibit a significant reduction in velocity but from borehole measurements densely fractured rocks do show significantly reduced velocities the amount of reduction generally proportional to the fracture density highly fractured rock and thick fault gouge along the creeping portion of the san andreas fault are evidenced by a pronounced seismic low velocity zone lvz which is either very thin or absent along locked portions of the fault thus there is a correlation between fault slip behavior and seismic velocity structure within the fault zone high pore pressure within the pronounced lvz may be conductive to fault creep deep seismic reflection data indicate that crustal faults sometimes extend through the entire crust models of these data and geologic evidence are consistent with a composition of deep faults consisting of highly foliated seismically anisotropic mylonites