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Sample records for adjacent fault segments

  1. Adjacent segment disease.

    PubMed

    Virk, Sohrab S; Niedermeier, Steven; Yu, Elizabeth; Khan, Safdar N

    2014-08-01

    EDUCATIONAL OBJECTIVES As a result of reading this article, physicians should be able to: 1. Understand the forces that predispose adjacent cervical segments to degeneration. 2. Understand the challenges of radiographic evaluation in the diagnosis of cervical and lumbar adjacent segment disease. 3. Describe the changes in biomechanical forces applied to adjacent segments of lumbar vertebrae with fusion. 4. Know the risk factors for adjacent segment disease in spinal fusion. Adjacent segment disease (ASD) is a broad term encompassing many complications of spinal fusion, including listhesis, instability, herniated nucleus pulposus, stenosis, hypertrophic facet arthritis, scoliosis, and vertebral compression fracture. The area of the cervical spine where most fusions occur (C3-C7) is adjacent to a highly mobile upper cervical region, and this contributes to the biomechanical stress put on the adjacent cervical segments postfusion. Studies have shown that after fusion surgery, there is increased load on adjacent segments. Definitive treatment of ASD is a topic of continuing research, but in general, treatment choices are dictated by patient age and degree of debilitation. Investigators have also studied the risk factors associated with spinal fusion that may predispose certain patients to ASD postfusion, and these data are invaluable for properly counseling patients considering spinal fusion surgery. Biomechanical studies have confirmed the added stress on adjacent segments in the cervical and lumbar spine. The diagnosis of cervical ASD is complicated given the imprecise correlation of radiographic and clinical findings. Although radiological and clinical diagnoses do not always correlate, radiographs and clinical examination dictate how a patient with prolonged pain is treated. Options for both cervical and lumbar spine ASD include fusion and/or decompression. Current studies are encouraging regarding the adoption of arthroplasty in spinal surgery, but more long

  2. Adjacent Segment Pathology after Lumbar Spinal Fusion.

    PubMed

    Lee, Jae Chul; Choi, Sung-Woo

    2015-10-01

    One of the major clinical issues encountered after lumbar spinal fusion is the development of adjacent segment pathology (ASP) caused by increased mechanical stress at adjacent segments, and resulting in various radiographic changes and clinical symptoms. This condition may require surgical intervention. The incidence of ASP varies with both the definition and methodology adopted in individual studies; various risk factors for this condition have been identified, although a significant controversy still exists regarding their significance. Motion-preserving devices have been developed, and some studies have shown their efficacy of preventing ASP. Surgeons should be aware of the risk factors of ASP when planning a surgery, and accordingly counsel their patients preoperatively. PMID:26435804

  3. Adjacent Segment Pathology after Lumbar Spinal Fusion

    PubMed Central

    Lee, Jae Chul

    2015-01-01

    One of the major clinical issues encountered after lumbar spinal fusion is the development of adjacent segment pathology (ASP) caused by increased mechanical stress at adjacent segments, and resulting in various radiographic changes and clinical symptoms. This condition may require surgical intervention. The incidence of ASP varies with both the definition and methodology adopted in individual studies; various risk factors for this condition have been identified, although a significant controversy still exists regarding their significance. Motion-preserving devices have been developed, and some studies have shown their efficacy of preventing ASP. Surgeons should be aware of the risk factors of ASP when planning a surgery, and accordingly counsel their patients preoperatively. PMID:26435804

  4. Probability of rupture of multiple fault segments

    USGS Publications Warehouse

    Andrews, D.J.; Schwerer, E.

    2000-01-01

    Fault segments identified from geologic and historic evidence have sometimes been adopted as features limiting the likely extends of earthquake ruptures. There is no doubt that individual segments can sometimes join together to produce larger earthquakes. This work is a trial of an objective method to determine the probability of multisegment ruptures. The frequency of occurrence of events on all conjectured combinations of adjacent segments in northern California is found by fitting to both geologic slip rates and to an assumed distribution of event sizes for the region as a whole. Uncertainty in the shape of the distribution near the maximum magnitude has a large effect on the solution. Frequencies of individual events cannot be determined, but it is possible to find a set of frequencies to fit a model closely. A robust conclusion for the San Francisco Bay region is that large multisegment events occur on the San Andreas and San Gregorio faults, but single-segment events predominate on the extended Hayward and Calaveras strands of segments.

  5. Adjacent Segment Pathology after Anterior Cervical Fusion.

    PubMed

    Chung, Jae Yoon; Park, Jong-Beom; Seo, Hyoung-Yeon; Kim, Sung Kyu

    2016-06-01

    Anterior cervical fusion has become a standard of care for numerous pathologic conditions of the cervical spine. However, subsequent development of clinically significant disc disease at levels adjacent to fused discs is a serious long-term complication of this procedure. As more patients live longer after surgery, it is foreseeable that adjacent segment pathology (ASP) will develop in increasing numbers of patients. Also, ASP has been studied more intensively with the recent popularity of motion preservation technologies like total disc arthroplasty. The true nature and scope of ASP remains poorly understood. The etiology of ASP is most likely multifactorial. Various factors including altered biomechanical stresses, surgical disruption of soft tissue and the natural history of cervical disc disease contribute to the development of ASP. General factors associated with disc degeneration including gender, age, smoking and sports may play a role in the development of ASP. Postoperative sagittal alignment and type of surgery are also considered potential causes of ASP. Therefore, a spine surgeon must be particularly careful to avoid unnecessary disruption of the musculoligamentous structures, reduced risk of direct injury to the disc during dissection and maintain a safe margin between the plate edge and adjacent vertebrae during anterior cervical fusion.

  6. Adjacent Segment Pathology after Anterior Cervical Fusion

    PubMed Central

    Chung, Jae Yoon; Park, Jong-Beom; Seo, Hyoung-Yeon

    2016-01-01

    Anterior cervical fusion has become a standard of care for numerous pathologic conditions of the cervical spine. However, subsequent development of clinically significant disc disease at levels adjacent to fused discs is a serious long-term complication of this procedure. As more patients live longer after surgery, it is foreseeable that adjacent segment pathology (ASP) will develop in increasing numbers of patients. Also, ASP has been studied more intensively with the recent popularity of motion preservation technologies like total disc arthroplasty. The true nature and scope of ASP remains poorly understood. The etiology of ASP is most likely multifactorial. Various factors including altered biomechanical stresses, surgical disruption of soft tissue and the natural history of cervical disc disease contribute to the development of ASP. General factors associated with disc degeneration including gender, age, smoking and sports may play a role in the development of ASP. Postoperative sagittal alignment and type of surgery are also considered potential causes of ASP. Therefore, a spine surgeon must be particularly careful to avoid unnecessary disruption of the musculoligamentous structures, reduced risk of direct injury to the disc during dissection and maintain a safe margin between the plate edge and adjacent vertebrae during anterior cervical fusion. PMID:27340541

  7. Adjacent Segment Disease Perspective and Review of the Literature

    PubMed Central

    Saavedra-Pozo, Fanor M.; Deusdara, Renato A. M.; Benzel, Edward C.

    2014-01-01

    Background Adjacent segment disease has become a common topic in spine surgery circles because of the significant increase in fusion surgery in recent years and the development of motion preservation technologies that theoretically should lead to a decrease in this pathology. The purpose of this review is to organize the evidence available in the current literature on this subject. Methods For this literature review, a search was conducted in PubMed with the following keywords: adjacent segment degeneration and disease. Selection, review, and analysis of the literature were completed according to level of evidence. Results The PubMed search identified 850 articles, from which 41 articles were selected and reviewed. The incidence of adjacent segment disease in the cervical spine is close to 3% without a significant statistical difference between surgical techniques (fusion vs arthroplasty). Authors report the incidence of adjacent segment disease in the lumbar spine to range from 2% to 14%. Damage to the posterior ligamentous complex and sagittal imbalances are important risk factors for both degeneration and disease. Conclusion Insufficient evidence exists at this point to support the idea that total disc arthroplasty is superior to fusion procedures in minimizing the incidence of adjacent segment disease. The etiology is most likely multifactorial but it is becoming abundantly clear that adjacent segment disease is not caused by motion segment fusion alone. Fusion plus the presence of abnormal end-fusion alignment appears to be a major factor in creating end-fusion stresses that result in adjacent segment degeneration and subsequent disease. The data presented cast further doubt on previously established rationales for total disc arthroplasty, at least with regard to the effect of total disc arthroplasty on adjacent segment degeneration pathology. PMID:24688337

  8. Analysis of adjacent segment reoperation after lumbar total disc replacement

    PubMed Central

    Rainey, Scott; Blumenthal, Scott L.; Zigler, Jack E.; Guyer, Richard D.; Ohnmeiss, Donna D.

    2012-01-01

    Background Fusion has long been used for treating chronic back pain unresponsive to nonoperative care. However, potential development of adjacent segment degeneration resulting in reoperation is a concern. Total disc replacement (TDR) has been proposed as a method for addressing back pain and preventing or reducing adjacent segment degeneration. The purpose of the study was to determine the reoperation rate at the segment adjacent to a level implanted with a lumbar TDR and to analyze the pre-TDR condition of the adjacent segment. Methods This study was based on a retrospective review of charts and radiographs from a consecutive series of 1000 TDR patients to identify those who underwent reoperation because of adjacent segment degeneration. Some of the patients were part of randomized studies comparing TDR with fusion. Adjacent segment reoperation data were also collected from 67 patients who were randomized to fusion in those studies. The condition of the adjacent segment before the index surgery was compared with its condition before reoperation based on radiographs, magnetic resonance imaging (MRI), and computed tomography. Results Of the 1000 TDR patients, 20 (2.0%) underwent reoperation. The mean length of time from arthroplasty to reoperation was 28.3 months (range, 0.5–85 months). Of the adjacent segments evaluated on preoperative MRI, 38.8% were normal, 38.8% were moderately diseased, and 22.2% were classified as having severe degeneration. None of these levels had a different grading at the time of reoperation compared with the pre-TDR MRI study. Reoperation for adjacent segment degeneration was performed in 4.5% of the fusion patients. Conclusions The 2.0% rate of adjacent segment degeneration resulting in reoperation in this study is similar to the 2.0% to 2.8% range in other studies and lower than the published rates of 7% to 18% after lumbar fusion. By carefully assessing the presence of pre-existing degenerative changes before performing arthroplasty

  9. Packaged Fault Model for Geometric Segmentation of Active Faults Into Earthquake Source Faults

    NASA Astrophysics Data System (ADS)

    Nakata, T.; Kumamoto, T.

    2004-12-01

    In Japan, the empirical formula proposed by Matsuda (1975) mainly based on the length of the historical surface fault ruptures and magnitude, is generally applied to estimate the size of future earthquakes from the extent of existing active faults for seismic hazard assessment. Therefore validity of the active fault length and defining individual segment boundaries where propagating ruptures terminate are essential and crucial to the reliability for the accurate assessments. It is, however, not likely for us to clearly identify the behavioral earthquake segments from observation of surface faulting during the historical period, because most of the active faults have longer recurrence intervals than 1000 years in Japan. Besides uncertainties of the datasets obtained mainly from fault trenching studies are quite large for fault grouping/segmentation. This is why new methods or criteria should be applied for active fault grouping/segmentation, and one of the candidates may be geometric criterion of active faults. Matsuda (1990) used _gfive kilometer_h as a critical distance for grouping and separation of neighboring active faults. On the other hand, Nakata and Goto (1998) proposed the geometric criteria such as (1) branching features of active fault traces and (2) characteristic pattern of vertical-slip distribution along the fault traces as tools to predict rupture length of future earthquakes. The branching during the fault rupture propagation is regarded as an effective energy dissipation process and could result in final rupture termination. With respect to the characteristic pattern of vertical-slip distribution, especially with strike-slip components, the up-thrown sides along the faults are, in general, located on the fault blocks in the direction of relative strike-slip. Applying these new geometric criteria to the high-resolution active fault distribution maps, the fault grouping/segmentation could be more practically conducted. We tested this model

  10. Testing simple models of brittle normal faulting: slip rate, spacing, and segmentation

    NASA Astrophysics Data System (ADS)

    Connolly, J.; Dawers, N. H.

    2005-05-01

    Fault growth and evolution is a complex process, however any predictable pattern will yield important information for assessing seismic hazard and clues to what controls fault behavior. Models of slip rate variation along strike, spacing of active faults, and scaling of segment length are investigated using data from faults located within the parabola of seismicity around the Yellowstone hotspot. Based on displacement-length relations and segment size, Cowie and Roberts used fault geometry to estimate along-strike slip rate variation in their 2001 paper (JSG,23,1901-1915). Following their model, along-strike slip rate profiles were calculated for three active normal faults: the Beaverhead, Lemhi, and Lost River faults. Though the method yields estimated slip rates, the results roughly mirror along-strike variation in total displacement, because the three faults are similar in size and age. The profiles indicate that the Beaverhead is underdisplaced, i.e. having a low slip rate relative to its length. This suggests that segment linkage occurred later in the development of the Beaverhead than in the others. Cowie and Roberts also proposed a model for fault spacing based on initial fault length and spacing, and maximum length and spacing of fully developed fault systems. Fault spacing is important in determining incidence and magnitude of fault movement. If the distance between faults is too small, strain becomes localized along one while the other exhibits a decrease in seismicity until no activity occurs. In practice it is impossible to know if the distance between the largest faults represents maximum fault spacing, because the fault population is still active and evolving; thus, it is difficult to test or implement the method. A relationship was found among faults within the study area, where spacing of adjacent active faults is proportional to the sums of their lengths. It was also observed that average segment length increases with increasing total fault length

  11. The relationship between oceanic transform fault segmentation, seismicity, and thermal structure

    NASA Astrophysics Data System (ADS)

    Wolfson-Schwehr, Monica

    analysis is used to model 3-D RTF fault geometry assuming a viscoplastic rheology in order to determine how segmentation affects the underlying thermal structure of the fault. In the models, fault segment length, length and location along fault of the intra-transform spreading center, and slip rate are varied. A new scaling relation is developed for the critical fault offset length (OC) that significantly reduces the thermal area of adjacent fault segments, such that adjacent segments are fully decoupled at ~4 OC . On moderate to fast slipping RTFs, offsets ≥ 5 km are sufficient to significantly reduce the thermal influence between two adjacent transform fault segments. The relationship between fault structure and seismic behavior was directly addressed on the Discovery transform fault, located at 4°S on the East Pacific Rise. One year of microseismicity recorded on an OBS array, and 24 years of Mw ≥ 5.4 earthquakes obtained from the Global Centroid Moment Tensor catalog, were correlated with surface fault structure delineated from high-resolution multibeam bathymetry. Each of the 15 Mw ≥ 5.4 earthquakes was relocated into one of five distinct repeating rupture patches, while microseismicity was found to be reduced within these patches. While the endpoints of these patches appeared to correlate with structural features on the western segment of Discovery, small step-overs in the primary fault trace were not observed at patch boundaries. This indicates that physical segmentation of the fault is not the primary control on the size and location of large earthquakes on Discovery, and that along-strike heterogeneity in fault zone properties must play an important role.

  12. Systematic Underestimation of Earthquake Magnitudes from Large Intracontinental Reverse Faults: Historical Ruptures Break Across Segment Boundaries

    NASA Technical Reports Server (NTRS)

    Rubin, C. M.

    1996-01-01

    Because most large-magnitude earthquakes along reverse faults have such irregular and complicated rupture patterns, reverse-fault segments defined on the basis of geometry alone may not be very useful for estimating sizes of future seismic sources. Most modern large ruptures of historical earthquakes generated by intracontinental reverse faults have involved geometrically complex rupture patterns. Ruptures across surficial discontinuities and complexities such as stepovers and cross-faults are common. Specifically, segment boundaries defined on the basis of discontinuities in surficial fault traces, pronounced changes in the geomorphology along strike, or the intersection of active faults commonly have not proven to be major impediments to rupture. Assuming that the seismic rupture will initiate and terminate at adjacent major geometric irregularities will commonly lead to underestimation of magnitudes of future large earthquakes.

  13. Analysis of adjacent segment degeneration with laminectomy above a fused lumbar segment.

    PubMed

    Gard, Andrew P; Klopper, Hendrik B; Doran, Stephen E; Hellbusch, Leslie C

    2013-11-01

    Although recent data suggests that lumbar fusion with decompression contributes to some marginal acceleration of adjacent segment degeneration (ASD), few studies have evaluated whether it is safe to perform a laminectomy above a fused segment. This study investigates the hypothesis that laminectomy above a fused lumbar segment does not increase the incidence of ASD, and assesses the benefits and risks of performing a laminectomy above a lumbar fusion. A retrospective review of 171 patients who underwent decompression and instrumented fusion of the lumbar spine was performed to analyze the association between ASD and laminectomy above the fused lumbar segment. Patients were divided into two groups - one group with instrumented fusion alone and the other group with instrumented fusion plus laminectomy above the fused segment. Of the 171 patients, 34 underwent additional decompressive laminectomy above the fused segment. There was a significant increase in ASD incidence as well as progression of ASD grade in both groups. There was no significant increase in ASD in patients with decompressive laminectomy above the fused lumbar segment compared to patients with laminectomy limited to the fused segment. This retrospective review of 171 patients who underwent decompression and instrumented fusion with follow-up radiographs demonstrates that laminectomy decompression above a fused segment does not significantly increase radiographic ASD. There is, however, a significant increase in ASD over time, which was observed throughout the entire cohort likely representing a natural progression of lumbar spondylosis above the fusion segment.

  14. Fault Segmentation and its Implication to the Evaluation of Future Earthquakes from Active Faults in Japan

    NASA Astrophysics Data System (ADS)

    Awata, Y.; Yoshioka, T.

    2005-12-01

    Segmentation of active faults is essential for the evaluation both of past and future faulting using geologic data from paleoseismological sites. A behavioral segment is defined as the smallest segment of fault having a characteristic history of faulting. More over, we have to estimate the earthquake segments that can be consist of multiple faulting along a system of behavioral segments. Active fault strands in Japan are segmented into behavioral segments based on fault discontinuity of 2-3 km and larger (Active Fault Res. Group, GSJ, 2000), large bend of fault strand and paleoseismicity. 431 behavioral segments, >= 10 km in length and >= 0.1 m/ky in long-term slip-rate, are identified from a database of active faults in Japan, that is constructed at AFRC, GSJ/AIST. The length of the segments is averaged 21 km and approximately 70 km in maximum. Only 8 segments are exceed 45 km in length. These lengths are very similar to those of historical surface ruptures not only in Japan since 1891 Nobi earthquake, but also in other regions having different tectonic setting. According to the scaling law between fault length and amount of displacement of behavioral segment, a maximum length of ca. 70 km can estimate a slip of ca. 14 m. This amount of slip is as large as world largest slip occurred during the 1931 Fuyun earthquake of M 8, 1999 Chichi earthquake of M 7.4 and the 2001 Central Kunlun earthquake of M 7.9 in East Asia. Recent geological and seismological studies on large earthquakes have revealed that multiple-rupturing is very common during large earthquakes. Therefore, evaluation of simultaneous faulting along a system of active faults is indispensable for the estimation of earthquake size. A Matsuda's (1990) idea of "seismogenic faults", that is divided or grouped based on the geometric discontinuity of 5 km, may useful for the best estimation of earthquake segment. The Japanese behavioral segments are grouped into "seismogenic faults", each consists of about 2

  15. Duplex structures connecting fault segments in Entrada Sandstone

    NASA Astrophysics Data System (ADS)

    Cruikshank, Kenneth M.; Zhao, Guozhu; Johnson, Arvid M.

    All stages in the development of a duplex structure—from isolated, stepped fault segments, to segments joined by a single ramp, to segments joined by tens of ramps—are preserved along strike-slip and normal faults in Entrada Sandstone in Arches National Park, Utah. Bedding is either absent or at a high angle to the duplex-like structures in Entrada Sandstone, thus it had no significant role in constraining their geometry. We can reproduce the essential features of a duplex structure along a normal fault with mechanical and kinematic models previously used to simulate duplex structures along thrust faults. However the models do not account for the amount of observed thickening at the step where the structure forms. This suggests that the geometry of duplex-like structures along these strike-slip faults may be a result of interaction between the fault segments.

  16. Repeated adjacent-segment degeneration after posterior lumbar interbody fusion.

    PubMed

    Okuda, Shinya; Oda, Takenori; Yamasaki, Ryoji; Maeno, Takafumi; Iwasaki, Motoki

    2014-05-01

    One of the most important sequelae affecting long-term results is adjacent-segment degeneration (ASD) after posterior lumbar interbody fusion (PLIF). Although several reports have described the incidence rate, there have been no reports of repeated ASD. The purpose of this report was to describe 1 case of repeated ASD after PLIF. A 62-year-old woman with L-4 degenerative spondylolisthesis underwent PLIF at L4-5. At the second operation, L3-4 PLIF was performed for L-3 degenerative spondylolisthesis 6 years after the primary operation. At the third operation, L2-3 PLIF was performed for L-2 degenerative spondylolisthesis 1.5 years after the primary operation. Vertebral collapse of L-1 was detected 1 year after the third operation, and the collapse had progressed. At the fourth operation, 3 years after the third operation, vertebral column resection of L-1 and replacement of titanium mesh cages with pedicle screw fixation between T-4 and L-5 was performed. Although the patient's symptoms resolved after each operation, the time between surgeries shortened. The sacral slope decreased gradually although each PLIF achieved local lordosis at the fused segment.

  17. Displacements and segment linkage in strike-slip fault zones

    NASA Astrophysics Data System (ADS)

    Peacock, D. C. P.

    Small-scale, well exposed strike-slip fault zones near Kirkcudbright, Scotland, cut sub-vertical bedding, so that mapped bed separations allow the displacements, linkage and evolution of fault segments to be assessed. Displacement variations along the segments can be related to lithologic variations, conjugate relationships, offsets, segment linkage and fault bends. High displacement gradients at the tips of conjugate and offset faults produce convex-upwards ( E-type) displacement-distance ( d-x) profiles. Contractional fault bends and linkage points are marked by a decrease in fault displacement, producing partially concave-upwards ( D-type) d-x profiles. Where fault displacement gradients are steep, wallrocks are marked by structures such as synthetic faults, normal drag folding, ductile strain and veining, which transfer displacement. The faults studied tend to have lower r/ dMAX ratios (where r = distance between the point of maximum displacement and the fault tip on a particular profile, and dMAX = maximum displacement on the profile) than are shown by normal faults in map view. This may be because r is measured parallel to the displacement direction and/or because of lithologic variations.

  18. Scaling Relations for the Thermal Structure of Segmented Oceanic Transform Faults

    NASA Astrophysics Data System (ADS)

    Wolfson-Schwehr, M.; Boettcher, M. S.; Behn, M. D.

    2015-12-01

    Mid-ocean ridge-transform faults (RTFs) are a natural laboratory for studying strike-slip earthquake behavior due to their relatively simple geometry, well-constrained slip rates, and quasi-periodic seismic cycles. However, deficiencies in our understanding of the limited size of the largest RTF earthquakes are due, in part, to not considering the effect of short intra-transform spreading centers (ITSCs) on fault thermal structure. We use COMSOL Multiphysics to run a series of 3D finite element simulations of segmented RTFs with visco-plastic rheology. The models test a range of RTF segment lengths (L = 10-150 km), ITSC offset lengths (O = 1-30 km), and spreading rates (V = 2-14 cm/yr). The lithosphere and upper mantle are approximated as steady-state, incompressible flow. Coulomb failure incorporates brittle processes in the lithosphere, and a temperature-dependent flow law for dislocation creep of olivine activates ductile deformation in the mantle. ITSC offsets as small as 2 km affect the thermal structure underlying many segmented RTFs, reducing the area above the 600˚C isotherm, A600, and thus the size of the largest expected earthquakes, Mc. We develop a scaling relation for the critical ITSC offset length, OC, which significantly reduces the thermal affect of adjacent fault segments of length L1 and L2. OC is defined as the ITSC offset that results in an area loss ratio of R = (Aunbroken - Acombined)/Aunbroken - Adecoupled) = 63%, where Aunbroken = C600(L1+L2)1.5V-0.6 is A600 for an RTF of length L1 + L2; Adecoupled = C600(L11.5+L21.5)V-0.6 is the combined A600 of RTFs of lengths L1 and L2, respectively; and Acombined = Aunbroken exp(-O/ OC) + Adecoupled (1-exp(-O/ OC)). C600 is a constant. We use OC and kinematic fault parameters (L1, L2, O, and V) to develop a scaling relation for the approximate seismogenic area, Aseg, for each segment of a RTF system composed of two fault segments. Finally, we estimate the size of Mc on a fault segment based on Aseg. We

  19. Radiologic Changes of Operated and Adjacent Segments after Anterior Cervical Microforaminotomy

    PubMed Central

    Ahn, Jang Ho; Park, Moon Sun; Kim, Seong Min; Chung, Seung Young; Lee, Do Sung

    2016-01-01

    Objective Anterior cervical microforaminotomy (ACMF) is a motion-preserving surgical procedure. The purpose of this study is to assess radiologic changes of operated and adjacent segments after ACMF. Methods We retrospectively reviewed 52 patients who underwent ACMF between 1998 and 2008. From X-ray film-based changes, disc height and sagittal range of motion (ROM) of operated and adjacent segments were compared at preoperative and last follow-up periods. Radiological degeneration of both segments was analyzed as well. Results The mean follow-up period was 48.2 months. There were 78 operated, 52 upper adjacent, and 38 lower adjacent segments. There were statistically significant differences in the ROM and disc height of operated segment between preoperative and last follow-up periods. However, there were no statistically significant differences in the ROM and disc height of adjacent segment between both periods. Radiological degenerative changes of operated segments were observed in 30%. That of adjacent segments was observed in 11 and 11% at upper and lower segments, respectively. Conclusion After mean 4-year follow-up periods, there were degenerative changes of operated segments. However, ACMF preserved motion and prevented degenerative changes of adjacent segments. PMID:27799993

  20. Fault current limiter with shield and adjacent cores

    DOEpatents

    Darmann, Francis Anthony; Moriconi, Franco; Hodge, Eoin Patrick

    2013-10-22

    In a fault current limiter (FCL) of a saturated core type having at least one coil wound around a high permeability material, a method of suppressing the time derivative of the fault current at the zero current point includes the following step: utilizing an electromagnetic screen or shield around the AC coil to suppress the time derivative current levels during zero current conditions.

  1. Correlation of data on strain accumulation adjacent to the San Andreas Fault with available models

    NASA Technical Reports Server (NTRS)

    Turcotte, Donald L.

    1986-01-01

    Theoretical and numerical studies of deformation on strike slip faults were performed and the results applied to geodetic observations performed in the vicinity of the San Andreas Fault in California. The initial efforts were devoted to an extensive series of finite element calculations of the deformation associated with cyclic displacements on a strike-slip fault. Measurements of strain accumulation adjacent to the San Andreas Fault indicate that the zone of strain accumulation extends only a few tens of kilometers away from the fault. There is a concern about the tendency to make geodetic observations along the line to the source. This technique has serious problems for strike slip faults since the vector velocity is also along the fault. Use of a series of stations lying perpendicular to the fault whose positions are measured relative to a reference station are suggested to correct the problem. The complexity of faulting adjacent to the San Andreas Fault indicated that the homogeneous elastic and viscoelastic approach to deformation had serious limitations. These limitation led to the proposal of an approach that assumes a fault is composed of a distribution of asperities and barriers on all scales. Thus, an earthquake on a fault is treated as a failure of a fractal tree. Work continued on the development of a fractal based model for deformation in the western United States. In order to better understand the distribution of seismicity on the San Andreas Fault system a fractal analog was developed. The fractal concept also provides a means of testing whether clustering in time or space is a scale-invariant process.

  2. Is the Troodos ophiolite (Cyprus) a complete, transform fault-bounded Neotethyan ridge segment?

    NASA Astrophysics Data System (ADS)

    Morris, Antony; Maffione, Marco

    2016-04-01

    We report new paleomagnetic data from the sheeted dike complex of the Troodos ophiolite (Cyprus) that indicate a hitherto unrecognized oceanic transform fault system marks its northern limit. The style, magnitude and scale of upper crustal fault block rotations in the northwestern Troodos region mirror those observed adjacent to the well-known Southern Troodos Transform Fault Zone along the southern edge of the ophiolite. A pattern of increasing clockwise rotation toward the north, coupled with consistent original dike strikes and inclined net rotation axes across this region, is compatible with distributed deformation adjacent to a dextrally-slipping transform system with a principal displacement zone just to the north of the exposed ophiolite. Combined with existing constraints on the spreading fabric, this implies segmentation of the Troodos ridge system on length scales of ~40 km, and suggests that a coherent strip of Neotethyan lithosphere, bounded by transforms and containing a complete ridge segment, has been uplifted to form the currently exposed Troodos ophiolite. Moreover, the inferred length scale of the ridge segment is consistent with formation at a slow-spreading rate during Tethyan seafloor spreading and with a supra-subduction zone environment, as indicated by geochemical constraints.

  3. Fault segmentation: New concepts from the Wasatch Fault Zone, Utah, USA

    NASA Astrophysics Data System (ADS)

    DuRoss, Christopher B.; Personius, Stephen F.; Crone, Anthony J.; Olig, Susan S.; Hylland, Michael D.; Lund, William R.; Schwartz, David P.

    2016-02-01

    The question of whether structural segment boundaries along multisegment normal faults such as the Wasatch fault zone (WFZ) act as persistent barriers to rupture is critical to seismic hazard analyses. We synthesized late Holocene paleoseismic data from 20 trench sites along the central WFZ to evaluate earthquake rupture length and fault segmentation. For the youngest (<3 ka) and best-constrained earthquakes, differences in earthquake timing across prominent primary segment boundaries, especially for the most recent earthquakes on the north-central WFZ, are consistent with segment-controlled ruptures. However, broadly constrained earthquake times, dissimilar event times along the segments, the presence of smaller-scale (subsegment) boundaries, and areas of complex faulting permit partial-segment and multisegment (e.g., spillover) ruptures that are shorter (~20-40 km) or longer (~60-100 km) than the primary segment lengths (35-59 km). We report a segmented WFZ model that includes 24 earthquakes since ~7 ka and yields mean estimates of recurrence (1.1-1.3 kyr) and vertical slip rate (1.3-2.0 mm/yr) for the segments. However, additional rupture scenarios that include segment boundary spatial uncertainties, floating earthquakes, and multisegment ruptures are necessary to fully address epistemic uncertainties in rupture length. We compare the central WFZ to paleoseismic and historical surface ruptures in the Basin and Range Province and central Italian Apennines and conclude that displacement profiles have limited value for assessing the persistence of segment boundaries but can aid in interpreting prehistoric spillover ruptures. Our comparison also suggests that the probabilities of shorter and longer ruptures on the WFZ need to be investigated.

  4. Fault segmentation: New concepts from the Wasatch Fault Zone, Utah, USA

    USGS Publications Warehouse

    Duross, Christopher; Personius, Stephen F.; Crone, Anthony J.; Olig, Susan S.; Hylland, Michael D.; Lund, William R.; Schwartz, David P.

    2016-01-01

    The question of whether structural segment boundaries along multisegment normal faults such as the Wasatch fault zone (WFZ) act as persistent barriers to rupture is critical to seismic hazard analyses. We synthesized late Holocene paleoseismic data from 20 trench sites along the central WFZ to evaluate earthquake rupture length and fault segmentation. For the youngest (<3 ka) and best-constrained earthquakes, differences in earthquake timing across prominent primary segment boundaries, especially for the most recent earthquakes on the north-central WFZ, are consistent with segment-controlled ruptures. However, broadly constrained earthquake times, dissimilar event times along the segments, the presence of smaller-scale (subsegment) boundaries, and areas of complex faulting permit partial-segment and multisegment (e.g., spillover) ruptures that are shorter (~20–40 km) or longer (~60–100 km) than the primary segment lengths (35–59 km). We report a segmented WFZ model that includes 24 earthquakes since ~7 ka and yields mean estimates of recurrence (1.1–1.3 kyr) and vertical slip rate (1.3–2.0 mm/yr) for the segments. However, additional rupture scenarios that include segment boundary spatial uncertainties, floating earthquakes, and multisegment ruptures are necessary to fully address epistemic uncertainties in rupture length. We compare the central WFZ to paleoseismic and historical surface ruptures in the Basin and Range Province and central Italian Apennines and conclude that displacement profiles have limited value for assessing the persistence of segment boundaries but can aid in interpreting prehistoric spillover ruptures. Our comparison also suggests that the probabilities of shorter and longer ruptures on the WFZ need to be investigated.

  5. Deformation mechanisms adjacent to a thrust fault, Sangre de Cristo Mountains, Colorado

    SciTech Connect

    Kelly, J.C.; McConnell, D.A.; Friberg, V.M. . Dept. of Geology)

    1994-04-01

    The purpose of this study is to examine the character of grain-scale deformation adjacent to a Laramide thrust fault in the Sangre de Cristo Mountains. This site represents a window through the hanging wall of a thrust sheet which juxtaposes Precambrian rocks over Pennsylvanian rocks. It provides a rare opportunity to examine deformation mechanisms in the footwall of a basement-involved thrust. Brittle deformation is evident at both outcrop and grain-scale. Filled fractures and slickensides composed of quartz and epidote are present throughout the area, and increase in abundance adjacent to the fault zone, as does the frequency of mesoscopic faulting. Variations in deformation mechanisms can be seen between the Precambrian rocks of the thrust sheet and the Pennsylvanian metasedimentary rocks, and between the metamorphosed arkoses and metapelites within the Pennsylvanian section. Cataclastic textures are present in deformed Precambrian rocks, and the degree of cataclasis is greatest immediately adjacent to the fault zone. Deformation in the Pennsylvanian rocks is largely dependent upon the abundance of fine-grained matrix within each sample. The degree of brittle deformation is negatively correlated to the percentage of matrix. Coarser-grained sections show microscopic faults which offset quartz and feldspar grains. Offsets decrease on the faults as they pass from coarse grains into the matrix.

  6. Generic along-strike segmentation of Afar normal faults, East Africa: Implications on fault growth and stress heterogeneity on seismogenic fault planes

    NASA Astrophysics Data System (ADS)

    Manighetti, I.; Caulet, C.; Barros, L.; Perrin, C.; Cappa, F.; Gaudemer, Y.

    2015-02-01

    Understanding how natural faults are segmented along their length can provide useful insights into fault growth processes, stress distribution on fault planes, and earthquake dynamics. We use cumulative displacement profiles to analyze the two largest scales of segmentation of ˜900 normal faults in Afar, East Africa. We build upon a prior study by Manighetti et al. (2009) and develop a new signal processing method aimed at recovering the number, position, displacement, and length of both the major (i.e., longest) and the subordinate, secondary segments within the faults. Regardless of their length, age, geographic location, total displacement, and slip rate, 90% of the faults contain two to five major segments, whereas more than 70% of these major segments are divided into two to four secondary segments. In each hierarchical rank of fault segmentation, most segments have a similar proportional length, whereas the number of segments slightly decreases with fault structural maturity. The along-strike segmentation of the Afar faults is thus generic at its two largest scales. We summarize published fault segment data on 42 normal, reverse, and strike-slip faults worldwide, and find a similar number (two to five) of major and secondary segments across the population. We suggest a fault growth scenario that might account for the generic large-scale segmentation of faults. The observation of a generic segmentation suggests that seismogenic fault planes are punctuated with a deterministic number of large stress concentrations, which are likely to control the initiation, arrest and hence extent and magnitude of earthquake ruptures.

  7. Paleostress adjacent to the Alpine Fault of New Zealand - Fault, vein, and styolite data from the Doctors Dome area

    NASA Astrophysics Data System (ADS)

    Nicol, Andrew; Wise, Donald U.

    1992-11-01

    Doctors Dome, 75 km north of Christchurch, New Zealand, is an early Pleistocene to Recent structure being deformed along the southeast edge of the Pacific-Australian plate boundary. Paleostress in the area has been determined in basement rocks of the Mesozoic meta-graywacke Torlesse Supergroup which lies unconformably beneath Cretaceous and younger cover rocks. Inversion of basement fault data for the area indicates a general northwest compression with two peaks, one WNW-ESE parallel to the shortening suggested by the older vein system and the other parallel to southeast-northwest stylolite columns in the cover rocks. This direction is approximately parallel to regional indicators of contemporary deformation in and adjacent to the Alpine Fault Zone and suggests that the stress field affecting these rocks has not changed significantly since the late Pliocene-early Pleistocene. Like the San Andreas system, this compression is at a high angle to the strike of the zone as a whole, but is compatible with the direction of plate convergence and motion of the major faults. Between the overlappig ends of the Alpine Fault and the Hikurangi Subduction Zone the Alpine Fault may become subhorizontal at middle-lower crustal levels, partially decoupling the crust from underlying structures, and thus allowing oblique motion to be transferred directly onto the fault from the subduction complex, while aiding the change from subduction to continental collision.

  8. Segmented infrared image analysis for rotating machinery fault diagnosis

    NASA Astrophysics Data System (ADS)

    Duan, Lixiang; Yao, Mingchao; Wang, Jinjiang; Bai, Tangbo; Zhang, Laibin

    2016-07-01

    As a noncontact and non-intrusive technique, infrared image analysis becomes promising for machinery defect diagnosis. However, the insignificant information and strong noise in infrared image limit its performance. To address this issue, this paper presents an image segmentation approach to enhance the feature extraction in infrared image analysis. A region selection criterion named dispersion degree is also formulated to discriminate fault representative regions from unrelated background information. Feature extraction and fusion methods are then applied to obtain features from selected regions for further diagnosis. Experimental studies on a rotor fault simulator demonstrate that the presented segmented feature enhancement approach outperforms the one from the original image using both Naïve Bayes classifier and support vector machine.

  9. Wasatch fault zone, Utah - segmentation and history of Holocene earthquakes

    USGS Publications Warehouse

    Machette, Michael N.; Personius, Stephen F.; Nelson, Alan R.; Schwartz, David P.; Lund, William R.

    1991-01-01

    The Wasatch fault zone (WFZ) forms the eastern boundary of the Basin and Range province and is the longest continuous, active normal fault (343 km) in the United States. It underlies an urban corridor of 1.6 million people (80% of Utah's population) representing the largest earthquake risk in the interior of the western United States. The authors have used paleoseismological data to identify 10 discrete segments of the WFZ. Five are active, medial segments with Holocene slip rates of 1-2 mm a-1, recurrence intervals of 2000-4000 years and average lengths of about 50 km. Five are less active, distal segments with mostly pre-Holocene surface ruptures, late Quaternary slip rates of <0.5 mm a-1, recurrence intervals of ???10,000 years and average lengths of about 20 km. Surface-faulting events on each of the medial segments of the WFZ formed 2-4-m-high scarps repeatedly during the Holocene. Paleoseismological records for the past 6000 years indicate that a major surface-rupturing earthquake has occurred along one of the medial segments about every 395 ?? 60 years. However, between about 400 and 1500 years ago, the WFZ experienced six major surface-rupturing events, an average of one event every 220 years, or about twice as often as expected from the 6000-year record. Evidence has been found that surface-rupturing events occurred on the WFZ during the past 400 years, a time period which is twice the average intracluster recurrence interval and equal to the average Holocene recurrence interval.

  10. Historic surface faulting in continental United States and adjacent parts of Mexico

    USGS Publications Warehouse

    Bonilla, M.G.

    1967-01-01

    This report summarizes geometric aspects of approximately 35 instances of historic faulting of the ground surface in the continental United States and adjacent parts of Mexico. This information is of immediate importance in the selection and evaluation of sites for vital structures such as nuclear power plants. The data are presented in a table and graphs which show the quantitative relations between various aspects of the faulting. Certain items in the table that are uncertain, poorly known, or not in the published literature are briefly described in the text.

  11. Along strike-slip faults, do fault segments exist and how long are they ? (Invited)

    NASA Astrophysics Data System (ADS)

    Klinger, Y.; Rockwell, T. K.; Cubas, N.; Souloumiac, P.

    2013-12-01

    The existence of relay zones and bends along strike-slip faults has long been recognized. The control of such geometrical asperities in initiation and arrest of seismic ruptures has been documented in many cases, suggesting they have a key role in the structure along strike of strike-slip faults. We produced dense slip distribution for two large strike-slip earthquakes, the 2001 Kunlun earthquake and the 1940 Imperial fault earthquake. In the Kunlun case we correlated satellite images acquired before and after the event to obtain a slip distribution of 1 point/km over 300 km. For the Imperial fault earthquake, we used a set of low altitude aerial photos that were flown just after the earthquake. The resolution of the photos is good enough to allow us to measure offsets of hundreds of plow lines along the trace of the rupture. In both cases the amplitude of the slip varies at a scale of several kilometers. In the case of Kunlun, the correlation between slip variations and jogs or side faults branching off the main rupture is straightforward. In the case of the Imperial fault, where long-term morphology is not preserved because of anthropic activities, still the slip distribution corresponds well with the slip patches determined independently by seismologists. These two examples strongly suggest that the segmentation of the fault controls the way seismic ruptures propagate along strike-slip faults. A more systematic exploration of slip maps derived from kinematic inversions of geophysical data shows that beyond variation due to different methodology and data, the lateral size of slip patches derived from such geophysical studies saturates around 20 km, independently of the earthquake magnitude. In parallel, using the available dataset of well documented ground ruptures maps for strike slip earthquakes, we designed an automatic procedure to quantify the minimum number of connected strait lines, approximating fault segment, needed to fit the rupture trace. The

  12. Fault segment linkage and growth of the Polopos transpressive fault zone and its influence on Pleistocene drainage captures (southeastern Betics).

    NASA Astrophysics Data System (ADS)

    Giaconia, F.; Booth-Rea, G.; Martínez-Martínez, J. M.; Azañón, J. M.; Villegas, I.

    2012-04-01

    The Polopos fault zoneis a dextral-reverse fault-system that developed under Neogene to Quaternary N/S to NNW/SSE convergence between Africa and Iberia. This fault zone is formed by three main fault segments, the North and South Gafarillos dextral strike-slip faults, and the North Alhamilla reverse fault. The whole fault zone with an approximate length of 30 km has an E/W to ESE/WNW orientation and helicoidal geometry that permits the transfer of oblique SE-directed shortening in Sierra Cabrera to NW-directed shortening along the North Alhamilla reverse fault via vertical dextral Gafarillos fault segments, in between. The north Alhamilla reverse fault to the west of the system produces a fault-propagation fold in the hangingwall and an overturned fold in the footwall cutting through early Tortonian turbidites and folded Quaternary alluvial fans at the north Alhamilla mountain front. The Quaternary paleo-topographic surface formed by the alluvial fan has been displaced approximately 100 m by reverse faulting after 400 - 70 ky with a slip rate ranging between 0.25 and 1.4 mm yr-1. The South Gafarillos fault includes several N90°-110°E-striking segments with dextral and reverse-dextral kinematics. This fault cuts through the southeastern limb of the Alhamilla anticline by a fault segment that separates the basement from Messinian sediments, meanwhile other segments in the Nijar basin further south cut through Pleistocene river strath-terraces.. During the late Miocene the locus of dextral displacement occurred along the North Gafarillos fault segment that linked to a reverse fault segment at the northeast of the Sierra Alhamilla . The North Gafarillos fault segment and its associated mountain front was sealed by Messinian reefs. Since the Messinian, recent fault activity migrated towards the south forming the South Gafarillos fault segments. Fault segment migration displaced the active oblique strike-slip-related mountain fronts from the north towards the southeast

  13. Best Merge Region Growing Segmentation with Integrated Non-Adjacent Region Object Aggregation

    NASA Technical Reports Server (NTRS)

    Tilton, James C.; Tarabalka, Yuliya; Montesano, Paul M.; Gofman, Emanuel

    2012-01-01

    Best merge region growing normally produces segmentations with closed connected region objects. Recognizing that spectrally similar objects often appear in spatially separate locations, we present an approach for tightly integrating best merge region growing with non-adjacent region object aggregation, which we call Hierarchical Segmentation or HSeg. However, the original implementation of non-adjacent region object aggregation in HSeg required excessive computing time even for moderately sized images because of the required intercomparison of each region with all other regions. This problem was previously addressed by a recursive approximation of HSeg, called RHSeg. In this paper we introduce a refined implementation of non-adjacent region object aggregation in HSeg that reduces the computational requirements of HSeg without resorting to the recursive approximation. In this refinement, HSeg s region inter-comparisons among non-adjacent regions are limited to regions of a dynamically determined minimum size. We show that this refined version of HSeg can process moderately sized images in about the same amount of time as RHSeg incorporating the original HSeg. Nonetheless, RHSeg is still required for processing very large images due to its lower computer memory requirements and amenability to parallel processing. We then note a limitation of RHSeg with the original HSeg for high spatial resolution images, and show how incorporating the refined HSeg into RHSeg overcomes this limitation. The quality of the image segmentations produced by the refined HSeg is then compared with other available best merge segmentation approaches. Finally, we comment on the unique nature of the hierarchical segmentations produced by HSeg.

  14. Relating fault geometry and aseismic slip along the Haiyuan fault creeping segment

    NASA Astrophysics Data System (ADS)

    Jolivet, R.; Candela, T.; Lasserre, C.; Renard, F.; Doin, M.; Klinger, Y.

    2012-12-01

    Recent observations point out the relationship between the fault geometry and earthquake rupture processes. Bends, jogs and other geometric features along faults are known to influence the initiation, the propagation and the arrest of large earthquakes. Space-based geodetic techniques, such as GPS or InSAR, allow to locate seismic asperities along faults by mapping and inverting inter-, co- and post-seismic surface displacement fields. Such methods outline in particular a clear relationship between the coseismic slip distribution and the fault surface geometry. Here, we intend to relate the inter-seismic fault behavior with the fault geometry. We focus on the Haiyuan fault, China, one of the major left-lateral fault system that accommodates relative block motion in Tibet. We study the junction area in between the 240 km-long, 1920 Mw8 Haiyuan earthquake rupture trace, to the east, and the eastern end of the millennial Tianzhu seismic gap that ruptured in the past onto Mw8 type earthquakes, to the west. This junction is marked by a 35 km-long creeping segment recently revealed by InsAR, limited to the east by a km-scale pull-apart basin. The average creep rate over the 2003-2009 period is 5±1 mm/yr and is equivalent to the present day tectonic loading rate, suggesting no strain accumulation during this period. We analyze in details how the creep distribution is related to geometric features along this creeping section. Here, we use Envisat data, spanning the 2003-2009 period, to map the along strike distribution and the temporal evolution of the surface creep. We analyze data from 1 descending and 2 ascending tracks using the ROI PAC processing chain combined with the NSBAS chain, developed to enhance coherence in areas of rough topography. We focus SAR images using a common doppler value and combine them into interferograms using an adaptive topographic spectral range filtering technique. We assume a linear dependence of the LOS phase with the topography to remove

  15. Preliminary Paleointensity Results Obtained Along Two Adjacent Ridge Segments of the East Pacific Rise (15o-17oN)

    NASA Astrophysics Data System (ADS)

    Cormier, M. H.; Carlut, J.; Kent, D. V.; Kent, D. V.

    2001-12-01

    The 16oN segment north of the Orozco transform fault is the shallowest and broadest along more than 5000 km of the East Pacific Rise (EPR) from 23oS to 23oN. Paleointensity experiments using the Thellier paleointensity method have been conducted on more than 35 lava samples along this magmatically inflated segment and along the more `typical' adjacent 17oN segment. Our goal is to constrain the timing and thus the emplacement mechanism of lava flows along the crest of the EPR. On-going detailed geochemical analysis on the same samples independently constrain the major lava flow sequences [Donnelly et al., Eos Trans, 79, p. F832, 1998]. Reliable preliminary results are obtained on multiple glassy basaltic samples from 25 dredges and wax cores samples. These are distributed over ~100 km along-axis, mainly within a few hundred meters (~2000 years) of the morphological axis. Our paleointensity dating technique relies on calibrated portions of the geomagnetic reference curve to constrain the timing of the lava fields. The inflated 16oN segment is characterized by very recent activities (probably less than 50 years old) along with much older flows (several hundreds years old). Samples collected off-axis and near the end of the 16oN segment have low paleointensities and are thus thought to be significantly older. There is also a weak tendency for older samples to occur along tectonized sections of the ridge axis, consistent with waning magmatism in those areas. With the help of geochemical data, flows are classified according to eruptive cycles along the neovolcanic zone.

  16. Earthquake recurrence and fault behavior on the Homestead Valley fault -- Central segment of the 1992 Landers surface rupture sequence

    SciTech Connect

    Cinti, F.R. ); Fumal, T.E.; Garvin, C.D.; Hamilton, J.C.; Powers, T.J.; Schwartz, D.P. )

    1993-04-01

    The 1992 M 7.5 Landers earthquake produced complex surface rupture on sections of the previously mapped Johnson Valley, Homestead Valley, and Emerson faults. The earthquake has raised questions about new faulting, characteristic earthquakes, and fault segmentation. To address these issues the authors initiated a study of both ruptured and unruptured fault segments, and report initial observations on the Homestead Valley fault (HVF). The authors site is located at the distal end of a large alluvial fan where 1992 right slip was 3 m, vertical slip was 40 cm, and the rupture followed pre-existing NE-facing scarps. Two trenches provide clear evidence of the two most recent pre-1992 surface faulting events. The trenches exposed alluvial fan and scarp derived colluvial deposits that are displaced and locally warped by both vertical strike-slip and low angle reverse-oblique( )-slip faults. At the main fault trace two pre-1992 colluvial wedges overlie a distinctive Bt soil horizon of late( ) Pleistocene age. Colluvium from the penultimate event has weak soil development, indicating a Holocene age for this faulting; apparent vertical displacement from this event is 35 cm, essentially the same as 1992. Preliminary observations indicate that recurrence of large magnitude earthquakes on faults of the Eastern California Shear Zone is one to two orders of magnitude longer than on major faults of the San Andreas system. The length of the HVF is short for this amount of offset, which suggests prior events may have also involved the rupture of multiple fault segments.

  17. Repeated adjacent segment diseases and fractures in osteoporotic patients: a case report

    PubMed Central

    Chen, Hsin-Yao; Chen, Chiu-Liang; Chen, Wei-Liang

    2016-01-01

    Background Pedicle screw instrumentation for treating spinal disorder is becoming increasingly widespread. Many studies have advocated its use to facilitate rigid fixation for spine; however, adjacent segmental disease is a known complication. Instrumented fusion for osteoporotic spines remains a significant challenge for spine surgeons. Prophylactic vertebroplasty for adjacent vertebra has been reported to reduce the complications of junctional compression fractures but has raised a new problem of vertebral subluxation. This case report is a rare and an extreme example with many surgical complications caused by repeated instrumented fusion for osteoporotic spine in a single patient. This patient had various complications including adjacent segmental disease, vertebral subluxation, and junctional fractures on radiographs and magnetic resonance images. Case presentation An 81-year-old Taiwanese woman underwent decompression and instrumented fusion of L4-L5 in Taiwan 10 years ago. Due to degenerative spinal stenosis of L3-L4 and L2-L3, she had decompression with instrumented fusion from L5 to L1 at the previous hospital. However, catastrophic vertebral subluxations with severe neurologic compromise occurred, and she underwent salvage surgeries twice with prolonged instrumented fusion from L5 to T2. The surgeries did not resolve her problems of spinal instability and neurologic complications. Eventually, the patient remained with a Frankel Grade C spinal cord injury. Conclusion Adjacent segmental disease, junctional fracture, and vertebral subluxation are familiar complications following instrumented spinal fusion surgeries for osteoporotic spines. Neurologic injuries following long instrumentation are often serious and difficult to address with surgery alone. Conservative treatments should always be contemplated as an alternative method for patients with poor bone stock. PMID:27555778

  18. Earthquakes, Segments, Bends, and Fault-Face Geology: Correlations Within the San Andreas System, California

    NASA Astrophysics Data System (ADS)

    Jachens, R. C.; Simpson, R. W.; Thurber, C. H.; Murray, J. R.

    2006-12-01

    Three-dimensional geologic maps of regions surrounding parts of the San Andreas Fault system reveal correlations between fault face geology and both short- and long-term behavior of the faults. The Loma Prieta fault segment that ruptured during the 1989 M6.9 earthquake, as defined by its aftershocks, closely corresponds to the subsurface reach (80 km long) where a large body of Logan gabbro is truncated at the fault, as defined by its magnetic anomaly. This Jurassic ophiolitic gabbro and its related rocks occupy an unusual fault-bounded basement block within Salinaa, a largely Cretaceous granitic terrane SW of the San Andreas Fault. The along-fault reach of the Logan gabbro also coincides with essentially the entire Santa Cruz Mountains left-bend in the San Andreas Fault. Rejecting a chance coincidence, the position of the Logan gabbro with respect to the left bend implies that the bend is fixed relative to Salinia and that the block NE of the San Andreas Fault has been forced to negotiate around the bend as the blocks moved past each other. Thus the basement rocks of the Logan block appear to define (control?) the Loma Prieta segment in terms both of short-term behavior (earthquakes) and long-term behavior (restraining bend fault geometry). The Parkfield segment of the San Andreas Fault also closely corresponds to a characteristic geologic unit in the NE face of the fault, the greenstone-rich Permanente terrane of the Franciscan Complex. The along-fault subsurface extent of the Permanente terrane at the fault face, as inferred from a recent 3D tomographic wavespeed model, corresponds to the reach filled by the aftershocks of the 2004 Parkfield earthquake. Furthermore, the 2004 co-seismic slip inferred from geodetic observations also coincides with the Permanente terrane at the fault face. To test whether these observations are directly related to the presence of the Permanente terrane along the fault face, we looked at fault behavior at the location of its offset

  19. The Ionian and Alfeo-Etna fault zones: New segments of an evolving plate boundary in the central Mediterranean Sea?

    NASA Astrophysics Data System (ADS)

    Polonia, A.; Torelli, L.; Artoni, A.; Carlini, M.; Faccenna, C.; Ferranti, L.; Gasperini, L.; Govers, R.; Klaeschen, D.; Monaco, C.; Neri, G.; Nijholt, N.; Orecchio, B.; Wortel, R.

    2016-04-01

    The Calabrian Arc is a narrow subduction-rollback system resulting from Africa/Eurasia plate convergence. While crustal shortening is taken up in the accretionary wedge, transtensive deformation accounts for margin segmentation along transverse lithospheric faults. One of these structures is the NNW-SSE transtensive fault system connecting the Alfeo seamount and the Etna volcano (Alfeo-Etna Fault, AEF). A second, NW-SE crustal discontinuity, the Ionian Fault (IF), separates two lobes of the CA subduction complex (Western and Eastern Lobes) and impinges on the Sicilian coasts south of the Messina Straits. Analysis of multichannel seismic reflection profiles shows that: 1) the IF and the AEF are transfer crustal tectonic features bounding a complex deformation zone, which produces the downthrown of the Western lobe along a set of transtensive fault strands; 2) during Pleistocene times, transtensive faulting reactivated structural boundaries inherited from the Mesozoic Tethyan domain which acted as thrust faults during the Messinian and Pliocene; and 3) the IF and the AEF, and locally the Malta escarpment, accommodate a recent tectonic event coeval and possibly linked to the Mt. Etna formation. Regional geodynamic models show that, whereas AEF and IF are neighboring fault systems, their individual roles are different. Faulting primarily resulting from the ESE retreat of the Ionian slab is expressed in the northwestern part of the IF. The AEF, on the other hand, is part of the overall dextral shear deformation, resulting from differences in Africa-Eurasia motion between the western and eastern sectors of the Tyrrhenian margin of northern Sicily, and accommodating diverging motions in the adjacent compartments, which results in rifting processes within the Western Lobe of the Calabrian Arc accretionary wedge. As such, it is primarily associated with Africa-Eurasia relative motion.

  20. Architecture and Segmentation of Strike-Slip Faults in Southern California

    NASA Astrophysics Data System (ADS)

    Sahakian, Valerie Jean

    This dissertation investigates the architecture and segmentation of fault structures in Southern California, using marine active-source seismic data. Onshore or marine fault geometry is often poorly constrained due to their location. This study employs marine active-source seismic data to image these structures, and further the current understanding of the hazards they pose to the region. With these data, this dissertation first improves the existing framework of knowledge of fault architecture in the Salton pull-apart basin, near the terminus of the Southern San Andreas Fault (SSAF). It investigates the evolution of the pull-apart basin in the Imperial-San Andreas fault system with reflection and refraction data, and provides important constraints regarding the interplay of faults and strain partitioning in this region. New data suggest the existence of a previously unknown fault in the Salton Sea, the Salton Trough Fault (STF). This transtensional fault is located just to the west of the eastern Salton Sea shoreline, and strikes approximately parallel to the SSAF terminus. Finally, this dissertation investigates the architecture and segmentation of the Newport-Inglewood/Rose Canyon (NIRC) fault zone offshore Southern California, using seismic data sets with unprecedented density and resolution. It identifies four main fault strands, with three main stepover boundaries, and presents possible rupture scenarios based on quantitative and qualitative assessments of throughgoing rupture at stepovers or segment boundaries.

  1. Fault strength in Marmara region inferred from the geometry of the principle stress axes and fault orientations: A case study for the Prince's Islands fault segment

    NASA Astrophysics Data System (ADS)

    Pinar, Ali; Coskun, Zeynep; Mert, Aydin; Kalafat, Dogan

    2015-04-01

    The general consensus based on historical earthquake data point out that the last major moment release on the Prince's islands fault was in 1766 which in turn signals an increased seismic risk for Istanbul Metropolitan area considering the fact that most of the 20 mm/yr GPS derived slip rate for the region is accommodated mostly by that fault segment. The orientation of the Prince's islands fault segment overlaps with the NW-SE direction of the maximum principle stress axis derived from the focal mechanism solutions of the large and moderate sized earthquakes occurred in the Marmara region. As such, the NW-SE trending fault segment translates the motion between the two E-W trending branches of the North Anatolian fault zone; one extending from the Gulf of Izmit towards Çınarcık basin and the other extending between offshore Bakırköy and Silivri. The basic relation between the orientation of the maximum and minimum principal stress axes, the shear and normal stresses, and the orientation of a fault provides clue on the strength of a fault, i.e., its frictional coefficient. Here, the angle between the fault normal and maximum compressive stress axis is a key parameter where fault normal and fault parallel maximum compressive stress might be a necessary and sufficient condition for a creeping event. That relation also implies that when the trend of the sigma-1 axis is close to the strike of the fault the shear stress acting on the fault plane approaches zero. On the other hand, the ratio between the shear and normal stresses acting on a fault plane is proportional to the coefficient of frictional coefficient of the fault. Accordingly, the geometry between the Prince's islands fault segment and a maximum principal stress axis matches a weak fault model. In the frame of the presentation we analyze seismological data acquired in Marmara region and interpret the results in conjuction with the above mentioned weak fault model.

  2. Clinical Experiences of Non-fusion Dynamic Stabilization Surgery for Adjacent Segmental Pathology after Lumbar Fusion

    PubMed Central

    Lee, Soo Eon; Kim, Hyun-Jib

    2016-01-01

    Background As an alternative to spinal fusion, non-fusion dynamic stabilization surgery has been developed, showing good clinical outcomes. In the present study, we introduce our surgical series, which involves non-fusion dynamic stabilization surgery for adjacent segment pathology (ASP) after lumbar fusion surgery. Methods Fifteen patients (13 female and 2 male, mean age of 62.1 years) who underwent dynamic stabilization surgery for symptomatic ASP were included and medical records, magnetic resonance images (MRI), and plain radiographs were retrospectively evaluated. Results Twelve of the 15 patients had the fusion segment at L4-5, and the most common segment affected by ASP was L3-4. The time interval between prior fusion and later non-fusion surgery was mean 67.0 months. The Visual Analog Scale and Oswestry Disability Index showed values of 7.4 and 58.5% before the non-fusion surgery and these values respectively declined to 4.2 and 41.3% postoperatively at 36 months (p=0.027 and p=0.018, respectively). During the mean 44.8 months of follow-up, medication of analgesics was also significantly reduced. The MRI grade for disc and central stenosis identified significant degeneration at L3-4, and similar disc degeneration from lateral radiographs was determined at L3-4 between before the prior fusion surgery and the later non-fusion surgery. After the non-fusion surgery, the L3-4 segment and the proximal segment of L2-3 were preserved in the disc, stenosis and facet joint whereas L1-2 showed disc degeneration on the last MRI (p=0.032). Five instances of radiologic ASP were identified, showing characteristic disc-space narrowing at the proximal segments of L1-2 and L2-3. However, no patient underwent additional surgery for ASP after non-fusion dynamic stabilization surgery. Conclusion The proposed non-fusion dynamic stabilization system could be an effective surgical treatment for elderly patients with symptomatic ASP after lumbar fusion. PMID:27162710

  3. Reduction in adjacent-segment degeneration after multilevel posterior lumbar interbody fusion with proximal DIAM implantation.

    PubMed

    Lu, Kang; Liliang, Po-Chou; Wang, Hao-Kuang; Liang, Cheng-Loong; Chen, Jui-Sheng; Chen, Tai-Been; Wang, Kuo-Wei; Chen, Han-Jung

    2015-08-01

    OBJECT Multilevel long-segment lumbar fusion poses a high risk for future development of adjacent-segment degeneration (ASD). Creating a dynamic transition zone with an interspinous process device (IPD) proximal to the fusion has recently been applied as a method to reduce the occurrence of ASD. The authors report their experience with the Device for Intervertebral Assisted Motion (DIAM) implanted proximal to multilevel posterior lumbar interbody fusion (PLIF) in reducing the development of proximal ASD. METHODS This retrospective study reviewed 91 cases involving patients who underwent 2-level (L4-S1), 3-level (L3-S1), or 4-level (L2-S1) PLIF. In Group A (42 cases), the patients received PLIF only, while in Group B (49 cases), an interspinous process device, a DIAM implant, was put at the adjacent level proximal to the PLIF construct. Bone resection at the uppermost segment of the PLIF was equally limited in the 2 groups, with preservation of the upper portion of the spinous process/lamina and the attached supraspinous ligament. Outcome measures included a visual analog scale (VAS) for low-back pain and leg pain and the Oswestry Disability Index (ODI) for functional impairment. Anteroposterior and lateral flexion/extension radiographs were used to evaluate the fusion status, presence and patterns of ASD, and mobility of the DIAM-implanted segment. RESULTS Solid interbody fusion without implant failure was observed in all cases. Radiographic ASD occurred in 20 (48%) of Group A cases and 3 (6%) of Group B cases (p < 0.001). Among the patients in whom ASD was identified, 9 in Group A and 3 in Group B were symptomatic; of these patients, 3 in Group A and 1 in Group B underwent a second surgery for severe symptomatic ASD. At 24 months after surgery, Group A patients fared worse than Group B, showing higher mean VAS and ODI scores due to symptoms related to ASD. At the final follow-up evaluations, as reoperations had been performed to treat symptomatic ASD in some

  4. Insights on the youngest segment of the Altyn Tagh fault: the Longmu Co - Gozha Co fault system, Western Tibet

    NASA Astrophysics Data System (ADS)

    Chevalier, M.; Li, H.; Pan, J.; Sun, Z.; Liu, D.; Wu, C.; Pei, J.; Xu, W.; Huang, X.

    2013-12-01

    The Longmu Co - Gozha Co left-lateral strike-slip fault system (LGCF) is located in the narrowest, highest, coldest and driest part of the remote western Tibetan Plateau. Three main faults, the Longmu Co, Gozha Co and Ashikule faults, from SW to NE, are clear and distinct right-stepping en-echelon faults that connect through an extension zone about halfway between the Altyn Tagh fault (ATF) and the Karakorum fault (KF), the two major strike-slip faults on the Tibetan Plateau. The ~500 km-long LGCF system merges to the NE with the horsetail splays of the western ATF, and to the SW, it connects with, and deforms the KF to create a 27 km-wide restraining double fault bend, near Bangong Lake. Recent tectonic-related events, such as the 1951 volcanic eruption along the Ashikule fault and the 2008 Mw7.2 Yutian earthquake, are additional evidence that the LGCF segment of the ATF constitutes its most recent segment and is currently still propagating to the SW. Other evidence include the fact that its initiation age (~9 Ma) is younger than that of the KF (>14-23 Ma). Although poorly quantitatively documented, partly due to its very remote location at very high elevation making it difficult for field studies, and because the LGCF system is located between two major active faults (ATF and KF) together forming a triple junction, quantifying its activity remains a key problem to understand the kinematics and the tectonics history of the westernmost Tibetan Plateau, and to correlate the various terranes identified eastwards and westwards. The Karakax fault (westernmost segment of the ATF), LGCF and KF together control the tectonics of Western Tibet which itself controls the extrusion of Tibet towards the east. Each of the three faults shows clear and impressive morphological indications of left-lateral active shear that leave no doubt about its left-lateral sense of shear, which is debated. Here, we use field observations, satellite images, topographic maps, total station

  5. Deformation microstructures and diagenesis in sandstone adjacent to an extensional fault: Implications for the flow and entrapment of hydrocarbons

    SciTech Connect

    Hippler, S.J. )

    1993-04-01

    Microstructural and diagenetic analyses of the North Scapa Sandstone in the hanging wall of the North Scapa fault, Orkney, Scotland, provide insight into the relationship between faulting and fluid flow during basin development. The results demonstrate the influence of this relationship on fault sealing processes and hydrocarbon migration. During development of the Orcadian basin in the Middle Devonian, the fault moved in an extensional sense. Dilatancy associated with cataclastic deformation caused localization of fluid flow and resulted in the precipitation of quartz and illite cement in the North Scapa Sandstone up to 1 m from the fault plane. This diagenetic event, coupled with cataclastic grain-size reduction, significantly reduced the porosity and permeability of the sandstone directly adjacent to the fault. These processes are effective sealing mechanisms within the sandstone. Lacustrine source rocks in the Orcadian basin reached maturation during the latest Devonian to middle Carboniferous. At the end of this time, the basin was uplifted, and the North Scapa fault was reactivated in a normal, but dominantly oblique-slip sense. This later deformation was accommodated directly outside the sealed zone and resulted in the development of broad (10-20 cm) breccia zones and narrow (<10 cm) cataclastic bands. Further dilatancy associated with the cataclastic deformation channelized hydrocarbon flow through the high-strain breccia zones and cataclastic bands. These observations indicate that fault activity that is broadly coincident with maturation and expulsion of hydrocarbons within a basin can directly influence the location of migration pathways. 81 refs., 14 figs., 1 tab.

  6. Investigating multiple fault rupture at the Salar del Carmen segment of the Atacama Fault System (northern Chile): Fault scarp morphology and knickpoint analysis

    NASA Astrophysics Data System (ADS)

    Ewiak, Oktawian; Victor, Pia; Oncken, Onno

    2015-02-01

    This study presents a new geomorphological approach to investigate the past activity and potential seismic hazard of upper crustal faults at the Salar del Carmen segment of the Atacama Fault System in the northern Chile forearc. Our contribution is based on the analysis of a large set of topographic profiles and allows extrapolating fault analysis from a few selected locations to distances of kilometers along strike of the fault. We detected subtle changes in the fault scarp geometry which may represent the number of paleoearthquakes experienced by the structure and extracted the cumulative and last incremental displacement along strike of the investigated scarps. We also tested the potential of knickpoints in channels crossing the fault scarps as markers for repeated fault rupture and proxies for seismic displacement. The number of paleoearthquakes derived from our analysis is 2-3, well in agreement with recent paleoseismological investigations, which suggest 2-3 earthquakes (Mw = 6.5-6.7) at the studied segments. Knickpoints record the number of events for about 55% of the analyzed profile pairs. Only few knickpoints represent the full seismic displacement, while most retain only a fraction of the displacement. The along-strike displacement distributions suggest fault growth from the center toward the tips and linkage of individual ruptures. Our approach also improves the estimation of paleomagnitudes in case of multiple fault rupture by allowing to quantify the last increment of displacement separately. Paleomagnitudes calculated from total segment length and the last increment of displacement (Mw = 6.5-7.1) are in agreement with paleoseismological results.

  7. Thrust fault segmentation and downward fault propagation in accretionary wedges: New Insights from 3D seismic reflection data

    NASA Astrophysics Data System (ADS)

    Orme, Haydn; Bell, Rebecca; Jackson, Christopher

    2016-04-01

    The shallow parts of subduction megathrust faults are typically thought to be aseismic and incapable of propagating seismic rupture. The 2011 Tohoku-Oki earthquake, however, ruptured all the way to the trench, proving that in some locations rupture can propagate through the accretionary wedge. An improved understanding of the structural character and physical properties of accretionary wedges is therefore crucial to begin to assess why such anomalously shallow seismic rupture occurs. Despite its importance, we know surprisingly little regarding the 3D geometry and kinematics of thrust network development in accretionary prisms, largely due to a lack of 3D seismic reflection data providing high-resolution, 3D images of entire networks. Thus our current understanding is largely underpinned by observations from analogue and numerical modelling, with limited observational data from natural examples. In this contribution we use PSDM, 3D seismic reflection data from the Nankai margin (3D Muroto dataset, available from the UTIG Academic Seismic Portal, Marine Geoscience Data System) to examine how imbricate thrust fault networks evolve during accretionary wedge growth. We unravel the evolution of faults within the protothrust and imbricate thrust zones by interpreting multiple horizons across faults and measuring fault displacement and fold amplitude along-strike; by doing this, we are able to investigate the three dimensional accrual of strain. We document a number of local displacement minima along-strike of faults, suggesting that, the protothrust and imbricate thrusts developed from the linkage of smaller, previously isolated fault segments. Although we often assume imbricate faults are likely to have propagated upwards from the décollement we show strong evidence for fault nucleation at shallow depths and downward propagation to intersect the décollement. The complex fault interactions documented here have implications for hydraulic compartmentalisation and pore

  8. The Longriqu fault zone, eastern Tibetan Plateau: Segmentation and Holocene behavior

    NASA Astrophysics Data System (ADS)

    Ansberque, Claire; Bellier, Olivier; Godard, Vincent; Lasserre, Cécile; Wang, Mingming; Braucher, Régis; Talon, Brigitte; Sigoyer, Julia; Xu, Xiwei; Bourlès, Didier L.

    2016-03-01

    The dextral Longriba fault system (LFS), ~300 km long and constituting of two fault zones, has recently been recognized as an important structure of the eastern Tibetan plateau (Sichuan province), as it accommodates a significant amount of the deformation induced by the ongoing Indo-Asian collision. Although previous paleoseismological investigations highlighted its high seismogenic potential, no systematic quantification of the dextral displacements along the fault system has been undertaken so far. As such information is essential to appraise fault behavior, we propose here a first detailed analysis of the segmentation of the Longriqu fault, the northern fault zone of the LFS, and an offset inventory of morphological features along the fault, using high-resolution Pleiades satellite images. We identify six major segments forming a mature fault zone. Offsets inventory suggests a characteristic coseismic displacement of ~4 m. Two alluvial fans, with minimum ages of 6.7 and 13.2 ka, respectively displaced by 23 ± 7 m and 40 ± 5 m, give an estimate of the maximal horizontal slip rate on the Longriqu fault of 3.2 ± 1.1 mm yr-1. As a result, a minimum ~1340 year time interval between earthquakes is expected.

  9. Older literature review of increased risk of adjacent segment degeneration with instrumented lumbar fusions

    PubMed Central

    Epstein, Nancy E.

    2016-01-01

    Background: Adjacent segment degeneration (ASD) following lumbar spine surgery occurs in up to 30% of cases, and descriptions of such changes are not new. Here, we review some of the older literature concerning the rate of ASD, typically more severe cephalad than caudad, and highly correlated with instrumented fusions. Therefore, for degenerative lumbar disease without frank instability, ASD would be markedly reduced by avoiding instrumented fusions. Methods: In a prior review, the newer literature regarding the frequency of ASD following lumbar instrumented fusions (e.g., transforaminal or posterior lumbar interbody fusions [TLIF/PLIF] fusions or occasionally, posterolateral fusions [PLFs]) was presented. Some studies cited an up to an 18.5% incidence of ASD following instrumented versus noninstrumented fusions/decompressions alone (5.6%). A review of the older literature similarly documents a higher rate of ASD following instrumented fusions performed for degenerative lumbar disease alone. Results: More frequent and more severe ASD follows instrumented lumbar fusions performed for degenerative lumbar disease without instability. Alternatively, this entity should be treated with decompressions alone or with noninstrumented fusions, without the addition of instrumentation. Conclusions: Too many studies assume that TLIF, PLIF, and even PLF instrumented fusions are the “gold standard of care” for dealing with degenerative disease of the lumbar spine without documented instability. It is time to correct that assumption, and reassess the older literature along with the new to confirm that decompression alone and noninstrumented fusion avoid significant morbidity and even potentially mortality attributed to unnecessary instrumentation. PMID:26904370

  10. Coseismic and Early Post-Seismic Slip Distributions of the 2012 Emilia (Northern Italy) Seismic Sequence: New Insights in the Faults Activation and Resulting Stress Changes on Adjacent Faults

    NASA Astrophysics Data System (ADS)

    Cheloni, D.; Giuliani, R.; D'Agostino, N.; Mattone, M.; Bonano, M.; Fornaro, G.; Lanari, R.; Reale, D.

    2015-12-01

    The 2012 Emilia sequence (main shocks Mw 6.1 May 20 and Mw 5.9 May 29) ruptured two thrust segments of a ~E-W trending fault system of the buried Ferrara Arc, along a portion of the compressional system of the Apennines that had remained silent during past centuries. Here we use the rupture geometry constrained by the aftershocks and new geodetic data (levelling, InSAR and GPS measurements) to estimate an improved coseismic slip distribution of the two main events. In addition, we use post-seismic displacements, described and analyzed here for the first time, to infer a brand new post-seismic slip distribution of the May 29 event in terms of afterslip on the same coseismic plane. In particular, in this study we use a catalog of precisely relocated aftershocks to explore the different proposed geometries of the proposed thrust segments that have been published so far and estimate the coseismic and post-seismic slip distributions of the ruptured planes responsible for the two main seismic events from a joint inversion of the geodetic data.Joint inversion results revealed that the two earthquakes ruptured two distinct planar thrust faults, characterized by single main coseismic patches located around the centre of the rupture planes, in agreement with the seismological and geological information pointing out the Ferrara and the Mirandola thrust faults, as the causative structures of the May 20 and May 29 main shocks respectively.The preferred post-seismic slip distribution related to the 29 May event, yielded to a main patch of afterslip (equivalent to a Mw 5.6 event) located westward and up-dip of the main coseismic patch, suggesting that afterslip was triggered at the edges of the coseismic asperity. We then use these co- and post-seismic slip distribution models to calculate the stress changes on adjacent fault.

  11. Kinematics and Fault Interaction of the Marmara Segment of the North Anatolian Fault Zone from Fault-Plane Solutions Based on a Refined High Precision Hypocenter Catalogue

    NASA Astrophysics Data System (ADS)

    Wollin, C.; Bohnhoff, M.; Küpperkoch, L.

    2015-12-01

    The North Anatolian Fault Zone (NAFZ) is separating the Eurasian and Anatolian plates representing a right-lateral transform plate boundary accommodating 20-30 mm annual slip. During the last seismic cycle the NAFZ has produced a series of large earthquakes that started in 1939 in Eastern Anatolia and has propagated westward towards the Istanbul-Marmara region. Here an up to 150 km long segment below the Sea of Marmara remains the only NAFZ segment that was not activated since 1766 representing a seismic gap hosting the potential for a magnitude up to 7.5 earthquake.Here we present a hypocenter catalogue for the Marmara section of the NAFZ which is a challenge since the fault is located offshore permitting no long-term on- or near fault stations. Using the Akaike Information Criterion applied on a characteristic function derived from higher order statistics as well as autoregressive forward prediction to automatically pick P- and S-onset times, we consistently analyze extensive waveform data provided by permanent seismic broadband stations of a combined regional seismic network with unprecedented station distribution.The quality of automatically determined travel times is carefully examined by comparing them to manual reference picks which were determined with a scheme emphasizing highest possible consistency and precision. The high accuracy obtained for the travel times results in an improved hypocenter catalog with fewer but well-located events that allow to image the major fault branches of the NAFZ below the Sea of Marmara.The large network aperture with lacking stations immediately above the seismicity along the fault and insufficient azimuthal station density prevents inversion for focal mechanisms of most single events. Therefore we form spatial seismicity clusters and calculate composite fault plane solutions. Resolving fault-zone geometry and kinematics allow to identify the currently active fault branches and to determine the currently ongoing processes

  12. Segmentation of fault networks determined from spatial clustering of earthquakes

    NASA Astrophysics Data System (ADS)

    Ouillon, G.; Sornette, D.

    2011-02-01

    We present a new method of data clustering applied to earthquake catalogs, with the goal of reconstructing the seismically active part of fault networks. We first use an original method to separate clustered events from uncorrelated seismicity using the distribution of volumes of tetrahedra defined by closest neighbor events in the original and randomized seismic catalogs. The spatial disorder of the complex geometry of fault networks is then taken into account by defining faults as probabilistic anisotropic kernels. The structure of those kernels is motivated by properties of discontinuous tectonic deformation and by previous empirical observations of the geometry of faults and of earthquake clusters at many spatial and temporal scales. Combining this a priori knowledge with information theoretical arguments, we propose the Gaussian mixture approach implemented in an expectation maximization (EM) procedure. A cross-validation scheme is then used that allows the determination of the number of kernels which provides an optimal data clustering of the catalog. This three-step approach is applied to a high-quality catalog of relocated seismicity following the 1986 Mount Lewis (Ml = 5.7) event in California. It reveals that events cluster along planar patches of about 2 km2, i.e., comparable to the size of the main event. The finite thickness of those clusters (about 290 m) suggests that events do not occur on well-defined and smooth Euclidean fault core surfaces but rather that there exist a deforming area and a damage zone surrounding faults which may be seismically active at depth. Finally, we propose a connection between our methodology and multiscale spatial analysis, based on the derivation of a spatial fractal dimension of about 1.8 for the set of hypocenters in the Mount Lewis area, consistent with recent observations on relocated catalogs.

  13. Active fault, fault growth and segment linkage along the Janauri anticline (frontal foreland fold), NW Himalaya, India

    NASA Astrophysics Data System (ADS)

    Malik, Javed N.; Shah, Afroz A.; Sahoo, Ajit K.; Puhan, B.; Banerjee, Chiranjib; Shinde, Dattatraya P.; Juyal, Navin; Singhvi, Ashok K.; Rath, Shishir K.

    2010-03-01

    The 100 km long frontal foreland fold — the Janauri anticline in NW Himalayan foothills represents a single segment formed due to inter-linking of the southern (JS1) and the northern (JS2) Janauri segments. This anticline is a product of the fault related fold growth that facilitated lateral propagation by acquiring more length and linkage of smaller segments giving rise to a single large segment. The linked portion marked by flat-uplifted surface in the central portion represents the paleo-water gap of the Sutlej River. This area is comparatively more active in terms of tectonic activity, well justified by the occurrence of fault scarps along the forelimb and backlimb of the anticline. Occurrence of active fault scarps on either side of the anticline suggests that the slip accommodated in the frontal part is partitioned between the main frontal thrust i.e. the Himalayan Frontal Thrust (HFT) and associated back-thrust. The uplift in the piedmont zone along southern portion of Janauri anticline marked by dissected younger hill range suggests fore-landward propagation of tectonic activity along newly developed Frontal Piedmont Thrust (FPT), an imbricated emergent thrust branching out from the HFT system. We suggests that this happened because the southern segment JS1 does not linked-up with the northwestern end of Chandigarh anticline segment (CS). In the northwestern end of the Janauri anticline, due to no structural asperity the tectonic activity on HFT was taken-up by two (HF1 — in the frontal part and HF2 — towards the hinterland side) newly developed parallel active faults ( Hajipur Fault) branched from the main JS2 segment. The lateral propagation and movements along HF1 and HF2 resulted in uplift of the floodplain as well as responsible for the northward shift of the Beas River. GPR and trench investigations suggest that earthquakes during the recent past were accompanied with surface rupture. OSL (optical stimulated luminescence) dates from the trench

  14. Continuity, segmentation and faulting type of active fault zones of the 2016 Kumamoto earthquake inferred from analyses of a gravity gradient tensor

    NASA Astrophysics Data System (ADS)

    Matsumoto, Nayuta; Yoshihiro, Hiramatsu; Sawada, Akihiro

    2016-10-01

    We analyze Bouguer anomalies in/around the focal region of the 2016 Kumamoto earthquake to examine features, such as continuity, segmentation and faulting type, of the active fault zones related to the earthquake. Several derivatives and structural parameters calculated from a gravity gradient tensor are applied to highlight the features. First horizontal and vertical derivatives, as well as a normalized total horizontal derivative, characterize well the continuous subsurface fault structure along the Futagawa fault zone. On the other hand, the Hinagu fault zone is not clearly detected by these derivatives, especially in the case of the Takano-Shirahata segment, suggesting a difference of cumulative vertical displacement between the two fault zones. The normalized total horizontal derivative and the dimensionality index indicate a discontinuity of the subsurface structure of the Hinagu fault zone, that is, a segment boundary between the Takano-Shirahata and the Hinagu segments. The aftershock distribution does not extend beyond this segment boundary. In other words, this segment boundary controls the southern end of the rupture area of the foreshock. We also recognize normal fault structures dipping to the northwest in some areas of the fault zones from estimations of dip angles.[Figure not available: see fulltext.

  15. Apparatus and methods for impingement cooling of an undercut region adjacent a side wall of a turbine nozzle segment

    DOEpatents

    Burdgick, Steven Sebastian; Itzel, Gary Michael

    2001-01-01

    A gas turbine nozzle segment has outer and inner bands. Each band includes a side wall, a cover and an impingement plate between the cover and nozzle wall defining two cavities on opposite sides of the impingement plate. Cooling steam is supplied to one cavity for flow through apertures of the impingement plate to cool the nozzle wall. The side wall of the band and inturned flange define with the nozzle wall an undercut region. The inturned flange has a plurality of apertures for directing cooling steam to cool the side wall between adjacent nozzle segments.

  16. Prevalence of adjacent segment disc degeneration in patients undergoing anterior cervical discectomy and fusion based on pre-operative MRI findings.

    PubMed

    Lundine, Kristopher M; Davis, Gavin; Rogers, Myron; Staples, Margaret; Quan, Gerald

    2014-01-01

    Anterior cervical discectomy and fusion (ACDF) is a widely accepted surgical treatment for symptomatic cervical spondylosis. Some patients develop symptomatic adjacent segment degeneration, occasionally requiring further treatment. The cause and prevalence of adjacent segment degeneration and disease is unclear at present. Proponents for motion preserving surgery such as disc arthroplasty argue that this technique may decrease the "strain" on adjacent discs and thus decrease the incidence of symptomatic adjacent segment degeneration. The purpose of this study was to assess the pre-operative prevalence of adjacent segment degeneration in patients undergoing ACDF. A database review of three surgeons' practice was carried out to identify patients who had undergone a one- or two-level ACDF for degenerative disc disease. Patients were excluded if they were operated on for recent trauma, had an inflammatory arthropathy (for example, rheumatoid arthritis), or had previous spine surgery. The pre-operative MRI of each patient was reviewed and graded using a standardised methodology. One hundred and six patient MRI studies were reviewed. All patients showed some evidence of intervertebral disc degeneration adjacent to the planned operative segment(s). Increased severity of disc degeneration was associated with increased age and operative level, but was not associated with sagittal alignment. Disc degeneration was more common at levels adjacent to the surgical level than at non-adjacent segments, and was more severe at the superior adjacent level compared with the inferior adjacent level. These findings support the theory that adjacent segment degeneration following ACDF is due in part to the natural history of cervical spondylosis.

  17. Mountain front migration and drainage captures related to fault segment linkage and growth: The Polopos transpressive fault zone (southeastern Betics, SE Spain)

    NASA Astrophysics Data System (ADS)

    Giaconia, Flavio; Booth-Rea, Guillermo; Martínez-Martínez, José Miguel; Azañón, José Miguel; Pérez-Romero, Joaquín; Villegas, Irene

    2013-01-01

    The Polopos E-W- to ESE-WNW-oriented dextral-reverse fault zone is formed by the North Alhamilla reverse fault and the North and South Gafarillos dextral faults. It is a conjugate fault system of the sinistral NNE-SSW Palomares fault zone, active from the late most Tortonian (≈7 Ma) up to the late Pleistocene (≥70 ky) in the southeastern Betics. The helicoidal geometry of the fault zone permits to shift SE-directed movement along the South Cabrera reverse fault to NW-directed shortening along the North Alhamilla reverse fault via vertical Gafarillos fault segments, in between. Since the Messinian, fault activity migrated southwards forming the South Gafarillos fault and displacing the active fault-related mountain-front from the north to the south of Sierra de Polopos; whilst recent activity of the North Alhamilla reverse fault migrated westwards. The Polopos fault zone determined the differential uplift between the Sierra Alhamilla and the Tabernas-Sorbas basin promoting the middle Pleistocene capture that occurred in the southern margin of the Sorbas basin. Continued tectonic uplift of the Sierra Alhamilla-Polopos and Cabrera anticlinoria and local subsidence associated to the Palomares fault zone in the Vera basin promoted the headward erosion of the Aguas river drainage that captured the Sorbas basin during the late Pleistocene.

  18. Precordial ST segment depression during acute inferior myocardial infarction: early thallium-201 scintigraphic evidence of adjacent posterolateral or inferoseptal involvement

    SciTech Connect

    Lew, A.S.; Weiss, A.T.; Shah, P.K.; Maddahi, J.; Peter, T.; Ganz, W.; Swan, H.J.; Berman, D.S.

    1985-02-01

    To investigate the myocardial perfusion correlates of precordial ST segment depression during acute inferior myocardial infarction, a rest thallium-201 scintigram and a closely timed 12 lead electrocardiogram were obtained within 6 hours of the onset of infarction in 44 patients admitted with their first acute inferior myocardial infarction. Thirty-six patients demonstrated precordial ST segment depression (group 1) and eight did not (group 2). A perfusion defect involving the inferior wall was present in all 44 patients. Additional perfusion defects of the adjacent posterolateral wall (n . 20), the ventricular septum (n . 9) or both (n . 6) were present in 35 of 36 patients from group 1 compared with only 1 of 8 patients from group 2 (p less than 0.001). There was no significant difference in the frequency of multivessel coronary artery disease or disease of the left anterior descending artery between group 1 and group 2 or between patients with and those without a thallium-201 perfusion defect involving the ventricular septum. Thus, precordial ST segment depression during an acute inferior myocardial infarction is associated with thallium-201 scintigraphic evidence of more extensive involvement of the adjacent posterolateral or inferoseptal myocardial segments, which probably reflects the extent and pattern of distribution of the artery of infarction, rather than the presence of coexistent multivessel coronary artery disease or disease of the left anterior descending artery.

  19. Slip rate of the Wadi Araba fault, southern segment of the Dead Sea fault, derived from GPS and geomorphic measurements

    NASA Astrophysics Data System (ADS)

    Klinger, Y.; Lebeon, M.; Amrat, A.; Agnon, A.; Meriaux, A.; Dorbath, L.; Baer, G.; Finkel, R.; Ruegg, J.; Charade, O.; Mayyas, O.; Ryerson, F.; Tapponnier, P.

    2007-12-01

    The Dead Sea Fault (DSF) accommodates the northward displacement of the Arabia plate relative to Sinai. Although it counts among the major strike-slip faults, no agreement has been reached yet about its slip rate, either instantaneous or longer term. Proposed values vary from 2 to 10 mm/yr. We present here an extensive study of the slip rate for the southern segment of DSF, Wadi Araba fault, based on GPS profiles and measurements of offset geomorphologic features, which ages are comprised between 10 and 350 kyr. We installed 17 campaign-style GPS sites distributed along 3 profiles perpendicular to Wadi Araba fault with far-field points up to 90 km away from the fault. The sites have been measured twice, in 1999 and in 2005, during 48h- long sessions. Measurements are complemented by data from permanent GPS stations in Israel. Using a locked fault model, we estimate the slip rate to be 4.9 ± 1.6 mm/yr over 6 years. Tests for possible creep on the fault show that if it exists it is not significant. To estimate the slip rate over longer periods of time, we targeted alluvial fans offset by the fault at 4 sites, that we mapped and sampled for 10Be cosmogenic dating. At one site, preferred offset of 46 ± 4 m of a surface dated at 11 ± 3 kyr yields a slip rate of 4.7 ± 1.9 mm/yr, in very good agreement with the present-day slip rate. At the other sites, preliminary reconstructions show offsets of ~600 m to ~5400 m with ages ranging from 50 to 350 kyr and suggest a preliminary slip rate of 4-9 mm/yr. Ongoing studies aim to better understand the history of the different lobes of the fans, from their emplacement to their abandonment, to reach a tighter constraint on the geomorphologic slip rate. Interestingly, the slip rates presented here, that have been determined along the same transects of the DSF, show good agreement despite differences of methodology (GPS and geomorphology). It suggests that discrepancies between slip rates determined at different time scales could

  20. Effect of Fault Segmentations on Simulation of Long-Period Earthquake Ground Motions and Seismic Load

    NASA Astrophysics Data System (ADS)

    Bykovtsev, A.; Research Team Of Geotechnical; Structural Engineers

    2010-12-01

    Effect of fault segmentation on simulation of long-period earthquake ground motions(LPEQM) and seismic load(SP) will be presented for sites located within 6 miles of an active fault. According to AASHTO guide(2009) seismic design for sites located within 6 miles of an active fault studies shall be considered to quantify near-fault effects on ground motions to determine if these could significantly influence the bridge response. It will be demonstrated that in near-field (D<6 miles) LPEQM may contain pulses with multiple oscillations which can cause severe nonlinear structural response, predictable only through nonlinear time-history analyses. The main question for discussion will be “IS IT APPROPRIATE TO USE SIMPLE BRUNE’S MODEL FOR OBSERVED TIME HISTORY WITH MULTIPLE OSCILLATIONS?” The widespread Brune’s Model proposed a simple interpretation method for the spectrum of a small earthquake. It was OK to characterize the observed spectrum by three parameters: low-frequency level proportional to the seismic moment; corner frequency; and power of high-frequency asymptotic decay. The secondary parameters are usually interpreted by an earthquake source model in which a FLAT CIRCULAR RUPTURE PLANE (FCRP) is formed spreading at a constant speed from the center with a uniform stress drop. I see an OUTSTANDING PROBLEM with this approach. 1. As a rule the OBSERVED RECORDS in time domain are DIFFERENT from those predicted for the FCRP MODEL, although the shapes of observed and theoretical amplitude spectra in frequency domain are roughly similar to each other. 2. The simulated time history for displacement for the FCRP is a single spike of a triangle-like shape. However, the OBSERVED TIME HISTORIES are composed of MANY OSCILLATIONS. Two reasons exist for explanations of these oscillations. 1. Traditional approach: Apparently, the seismic signal arrives along multiple paths due to inhomogeneous structure and spreads over a time length which increases with travel

  1. Depth segmentation of fault slip: deep rupture in the 2011 Van Earthquake leaves shallow hazard

    NASA Astrophysics Data System (ADS)

    Elliott, J. R.; Copley, A.; Holley, R.; Scharer, K.; Parsons, B.

    2013-12-01

    We use InSAR, body-wave seismology, satellite imagery and field observations to constrain the fault parameters of the Mw 7.1 2011 Van (Eastern Turkey) reverse-slip earthquake, in the Turkish-Iranian Plateau. Distributed slip models from elastic dislocation modelling of the InSAR surface displacements from ENVISAT and COSMO-SkyMed interferograms indicate up to 9 m of reverse and oblique slip on a pair of en echelon NW 40-54 degree dipping fault planes which have surface extensions projecting to just 10 km north of the city of Van. The slip remained buried and is relatively deep, with a centroid depth of 14 km, and the rupture reaching only within 8--9 km of the surface, consistent with the lack of significant ground rupture. The up-dip extension of this modelled WSW-striking fault plane coincides with field observations of weak ground deformation seen on the western of the two fault segments, and has a dip consistent with that seen at the surface in fault gouge exposed in Quaternary sediments. No significant coseismic slip is found in the upper 8 km of the crust above the main slip patches, except for a small region on the eastern segment potentially resulting from the Mw 5.9 aftershock the same day. We perform extensive resolution tests on the data to confirm the robustness of the observed slip deficit in the shallow crust. We resolve a steep gradient in displacement at the point where the planes of the two fault segments ends are inferred to abut at depth, possibly exerting some structural control on rupture extent. This leaves an unruptured up-dip fault width of 8-11. Given that the surface trace of the fault is clearly visible in the geomorphology of the mountain range to the north of Van, and that fault gouge was found in Quaternary sediments at the surface, it is very likely that the upper portion of the crust is seismogenic. A rupture along a similar fault length of 30 km across the remaining unruptured fault width of 10 km, with a similar average slip of 3 m

  2. Mechanical and Microphysical Constraints on Co-seismic Rupture into the Creeping Segment of the San Andreas Fault

    NASA Astrophysics Data System (ADS)

    French, M. E.; Chester, F. M.; Chester, J. S.

    2014-12-01

    Experimentally-determined mechanical properties of clay-rich fault rock, and the associated micromechanical processes, are used to constrain the conditions of slip instability along the San Andreas Fault (SAF). Using smectite-rich fault gouge collected from the Central Deforming Zone (CDZ) of the SAF in the San Andreas Fault Observatory at Depth (SAFOD), rotary and triaxial shear deformation experiments were conducted at rates that correspond to co-seismic slip (1 m/s) and in-situ creep (~10-10 s-1). Frictional strength depends on rate, temperature, availability of pore water, and fabric development, all of which reflect operation of different microscopic mechanisms at high and low shear rates. On the basis of the results, we use an energy balance for a propagating rupture to evaluate the potential for seismic slip along the CDZ. Appropriate scaling of the gouge strength from experimental to in-situ conditions, particularly for seismic slip rates, is critical to evaluating seismic hazards. Accordingly, the micromechanical processes identified from results of the deformation experiments are used to constrain and evaluate several different scaling relations between strength, critical displacement, and normal stress for the CDZ gouge. Experiments show that, at in situ creep rates, dislocation glide in clay is the rate-controlling mechanism and is responsible for the low strength (μ = 0.11), which limits the potential energy available for sustaining co-seismic frictional slip. As a consequence, microseismic patches within the CDZ are predicted to arrest for all scaling relationships under in-situ deformation conditions. Dynamic weakening at co-seismic rates involves thermal fluid pressurization, and for some scaling relations may be sufficient to sustain propagation of a rupture that nucleates within the adjacent locked segment into the CDZ

  3. Analysis of regional deformation and strain accumulation data adjacent to the San Andreas fault

    NASA Technical Reports Server (NTRS)

    Turcotte, Donald L.

    1991-01-01

    A new approach to the understanding of crustal deformation was developed under this grant. This approach combined aspects of fractals, chaos, and self-organized criticality to provide a comprehensive theory for deformation on distributed faults. It is hypothesized that crustal deformation is an example of comminution: Deformation takes place on a fractal distribution of faults resulting in a fractal distribution of seismicity. Our primary effort under this grant was devoted to developing an understanding of distributed deformation in the continental crust. An initial effort was carried out on the fractal clustering of earthquakes in time. It was shown that earthquakes do not obey random Poisson statistics, but can be approximated in many cases by coupled, scale-invariant fractal statistics. We applied our approach to the statistics of earthquakes in the New Hebrides region of the southwest Pacific because of the very high level of seismicity there. This work was written up and published in the Bulletin of the Seismological Society of America. This approach was also applied to the statistics of the seismicity on the San Andreas fault system.

  4. Impulsive radon emanation on a creeping segment of the San Andreas fault, California

    USGS Publications Warehouse

    King, C.-Y.

    1985-01-01

    Radon emanation was continuously monitored for several months at two locations along a creeping segment of the San Andreas fault in central California. The recorded emanations showed several impulsive increases that lasted as much as five hours with amplitudes considerably larger than meteorologically induced diurnal variations. Some of the radon increases were accompanied or followed by earthquakes or fault-creep events. They were possibly the result of some sudden outbursts of relatively radon-rich ground gas, sometimes triggered by crustal deformation or vibration. ?? 1985 Birkha??user Verlag.

  5. Characterization of the Hosgri Fault Zone and adjacent structures in the offshore Santa Maria Basin, south-central California: Chapter CC of Evolution of sedimentary basins/onshore oil and gas investigations - Santa Maria province

    USGS Publications Warehouse

    Willingham, C. Richard; Rietman, Jan D.; Heck, Ronald G.; Lettis, William R.

    2013-01-01

    The Hosgri Fault Zone trends subparallel to the south-central California coast for 110 km from north of Point Estero to south of Purisima Point and forms the eastern margin of the present offshore Santa Maria Basin. Knowledge of the attributes of the Hosgri Fault Zone is important for petroleum development, seismic engineering, and environmental planning in the region. Because it lies offshore along its entire reach, our characterizations of the Hosgri Fault Zone and adjacent structures are primarily based on the analysis of over 10,000 km of common-depth-point marine seismic reflection data collected from a 5,000-km2 area of the central and eastern parts of the offshore Santa Maria Basin. We describe and illustrate the along-strike and downdip geometry of the Hosgri Fault Zone over its entire length and provide examples of interpreted seismic reflection records and a map of the structural trends of the fault zone and adjacent structures in the eastern offshore Santa Maria Basin. The seismic data are integrated with offshore well and seafloor geologic data to describe the age and seismic appearance of offshore geologic units and marker horizons. We develop a basin-wide seismic velocity model for depth conversions and map three major unconformities along the eastern offshore Santa Maria Basin. Accompanying plates include maps that are also presented as figures in the report. Appendix A provides microfossil data from selected wells and appendix B includes uninterpreted copies of the annotated seismic record sections illustrated in the chapter. Features of the Hosgri Fault Zone documented in this investigation are suggestive of both lateral and reverse slip. Characteristics indicative of lateral slip include (1) the linear to curvilinear character of the mapped trace of the fault zone, (2) changes in structural trend along and across the fault zone that diminish in magnitude toward the ends of the fault zone, (3) localized compressional and extensional structures

  6. A Model of Evolution of Fault Structure in Porous Sandstone Reflecting the Effect of Geometric Irregularities Associated with Early-Formed Segment Linkages

    NASA Astrophysics Data System (ADS)

    Schafer, K. W.; Johnson, B.

    2001-12-01

    We propose a model of the early evolution of the structure of strike-slip faults in porous sandstone based upon detailed maps of faults with small displacements (mm to decimeters) in the Hickory Sandstone in central Texas and the Navajo Sandstone near Moab, UT. We assume faults at a given site follow similar evolutionary paths and infer relative timing of formation of fault elements using cross cutting and high-angle abutment relationships. Faults consist of a network of hard-linked smaller segments. The number of fault segments varies along a fault and qualitatively become more numerous and preferentially clustered with increasing displacement. Lacunarity analyses and variograms of spatial density of fault segments quantitatively document the clustering of fault segments. Consistent with earlier work, we infer that faults evolve in the initial stage by linkage of an early-formed array of en echelon small faults that typically step opposite to the sense of shear. Linkage is by one of two geometrically and kinematically distinct linkage structures. With increasing fault displacement, new fault segments are preferentially added in close proximity to or within the early linkages. Accreted segments typically are arcuate and abut earlier segments at a high angle. Consequently, the spatial density of fault segments varies episodically along the fault. Early linkage structures represent geometric irregularities (roughness) along the evolving fault that we interpret to result in geometric stress concentrations that preferentially localize formation of new fault segments. This conceptual model does not demand the commonly assumed strain-hardening of the gouge of individual fault segments in order to explain the evolving complexity of fault structure with increasing displacement. The lack of an implied strain-hardening behavior is consistent with laboratory-scale fault development in porous sandstone.

  7. An induced seismicity experiment across a creeping segment of the Philippine Fault

    NASA Astrophysics Data System (ADS)

    Prioul, R.; Cornet, F. H.; Dorbath, C.; Dorbath, L.; Ogena, M.; Ramos, E.

    2000-06-01

    The location of seismicity induced by forced fluid flow provides information about domains of pore pressure variation, while changes in fluid content are identified through changes in seismic velocity. These effects have been investigated in the geothermal field of Tongonan, which lies on a creeping portion of the Philippine Fault on Ley te Island. Locally, the left-lateral strike-slip Philippine Fault branches out into three subparallel segments (Eastern, Central and Western Fault Lines). In June-July 1997, a water stimulation was undertaken in a well that intersects the Central Fault Line 1980 m below ground surface; 36,000 m3 were injected between the casing shoe at 1308 m and the well bottom at 2177 m. The seismicity was monitored with a surface station network of 18 stations. More than 400 events, induced by the injection experiment as well as by routine injections associated with the geothermal field exploitation, were recorded in the vicinity of the well. They have been located through a simultaneous three-dimensional (3-D) velocity-hypocenter inversion procedure. None of the microearthquakes are located along the Central Fault Line, they all occurred below the casing shoe to the east of the fault line, i.e., within the geothermal reservoir and mostly below the bottom of the well. Results from the injection experiment and the 18 months of seismic monitoring along the Central and West Fault Lines suggest an aseismic behavior of this major continental fault at this location. The 3-D velocity model, determined from the travel time inversion for seismic events observed during injections, is compared to that obtained from seismic monitoring conducted prior to any injection activities. An increase of P wave velocity is observed during the water injection. This velocity increase is localized within the seismicity cloud and is interpreted as an increase in liquid content within the initial liquid-vapor multiphase part of the reservoir.

  8. Stable creeping fault segments can become destructive as a result of dynamic weakening.

    PubMed

    Noda, Hiroyuki; Lapusta, Nadia

    2013-01-24

    Faults in Earth's crust accommodate slow relative motion between tectonic plates through either similarly slow slip or fast, seismic-wave-producing rupture events perceived as earthquakes. These types of behaviour are often assumed to be separated in space and to occur on two different types of fault segment: one with stable, rate-strengthening friction and the other with rate-weakening friction that leads to stick-slip. The 2011 Tohoku-Oki earthquake with moment magnitude M(w) = 9.0 challenged such assumptions by accumulating its largest seismic slip in the area that had been assumed to be creeping. Here we propose a model in which stable, rate-strengthening behaviour at low slip rates is combined with coseismic weakening due to rapid shear heating of pore fluids, allowing unstable slip to occur in segments that can creep between events. The model parameters are based on laboratory measurements on samples from the fault of the M(w) 7.6 1999 Chi-Chi earthquake. The long-term slip behaviour of the model, which we examine using a unique numerical approach that includes all wave effects, reproduces and explains a number of both long-term and coseismic observations-some of them seemingly contradictory-about the faults at which the Tohoku-Oki and Chi-Chi earthquakes occurred, including there being more high-frequency radiation from areas of lower slip, the largest seismic slip in the Tohoku-Oki earthquake having occurred in a potentially creeping segment, the overall pattern of previous events in the area and the complexity of the Tohoku-Oki rupture. The implication that earthquake rupture may break through large portions of creeping segments, which are at present considered to be barriers, requires a re-evaluation of seismic hazard in many areas. PMID:23302798

  9. Holocene behavior of the Brigham City segment: implications for forecasting the next large-magnitude earthquake on the Wasatch fault zone, Utah

    USGS Publications Warehouse

    Personius, Stephen F.; DuRoss, Christopher B.; Crone, Anthony J.

    2012-01-01

    The Brigham City segment (BCS), the northernmost Holocene‐active segment of the Wasatch fault zone (WFZ), is considered a likely location for the next big earthquake in northern Utah. We refine the timing of the last four surface‐rupturing (~Mw 7) earthquakes at several sites near Brigham City (BE1, 2430±250; BE2, 3490±180; BE3, 4510±530; and BE4, 5610±650 cal yr B.P.) and calculate mean recurrence intervals (1060–1500  yr) that are greatly exceeded by the elapsed time (~2500  yr) since the most recent surface‐rupturing earthquake (MRE). An additional rupture observed at the Pearsons Canyon site (PC1, 1240±50 cal yr B.P.) near the southern segment boundary is probably spillover rupture from a large earthquake on the adjacent Weber segment. Our seismic moment calculations show that the PC1 rupture reduced accumulated moment on the BCS about 22%, a value that may have been enough to postpone the next large earthquake. However, our calculations suggest that the segment currently has accumulated more than twice the moment accumulated in the three previous earthquake cycles, so we suspect that additional interactions with the adjacent Weber segment contributed to the long elapse time since the MRE on the BCS. Our moment calculations indicate that the next earthquake is not only overdue, but could be larger than the previous four earthquakes. Displacement data show higher rates of latest Quaternary slip (~1.3  mm/yr) along the southern two‐thirds of the segment. The northern third likely has experienced fewer or smaller ruptures, which suggests to us that most earthquakes initiate at the southern segment boundary.

  10. Plate convergence, transcurrent faults and internal deformation adjacent to Southeast Asia and the western Pacific

    NASA Technical Reports Server (NTRS)

    Fitch, T. J.

    1971-01-01

    A model for oblique convergence between plates of lithosphere is proposed in which at least a fraction of slip parallel to the plate margin results in transcurrent movements on a nearly vertical fault which is located on the continental side of a zone of plate consumption. In an extreme case of complete decoupling only the component of slip normal to the plate margin can be inferred from underthrusting. Recent movements in the western Sunda region provide the most convincing evidence for decoupling of slip, which in this region is thought to be oblique to the plate margin. A speculative model for convergence along the margins of the Philippine Sea is constructed from an inferred direction of oblique slip in the Philippine region. This model requires that the triple point formed by the junction of the Japanese and Izu-Bonin trenches and the Nankai trough migrate along the Sagami trough.

  11. Magnetic resonance imaging on disc degeneration changes after implantation of an interspinous spacer and fusion of the adjacent segment

    PubMed Central

    Liu, Xiaokang; Liu, Yingjie; Lian, Xiaofeng; Xu, Jianguang

    2015-01-01

    The aim of the study was to investigate the changes of the lumbar intervertebral disc degeneration by magnetic resonance imaging (MRI) after the implantation of interspinous device and the fusion of the adjacent segment. A total of 62 consecutive patients suffering L5/S1 lumbar disc herniation (LDH) with concomitant disc space narrowing or low-grade instability up to 5 mm translational slip in L5/S1 level were treated with lumbar interbody fusion (LIF) via posterior approach. Thirty-four of these patients (Coflex group) received an additional implantation of the interspinous spacer device (Coflex™) in the level L4/L5, while the rest of 28 patients (fusion group) underwent the fusion surgery alone. Clinical and radiographic examinations were performed at pre- and postoperative visits to compare the clinical outcomes and the changes of the L4/L5 vertebral disc degeneration on MRI in both Coflex and fusion group. Although both Coflex and fusion group showed improvements of the clinical outcomes assessed by the Oswestry Disability Index (ODI) after surgery, patients in Coflex group had more significant amelioration (P < 0.05) compared to fusion group. During follow up, the postoperative disc degeneration changes in Coflex group assessed by the relative signal intensity (RSI) differed from those in fusion group (P < 0.05). The supplemental implantation of Coflex™ after the fusion surgery could delay the disc degeneration of the adjacent segment. PMID:26131210

  12. Magnetic resonance imaging on disc degeneration changes after implantation of an interspinous spacer and fusion of the adjacent segment.

    PubMed

    Liu, Xiaokang; Liu, Yingjie; Lian, Xiaofeng; Xu, Jianguang

    2015-01-01

    The aim of the study was to investigate the changes of the lumbar intervertebral disc degeneration by magnetic resonance imaging (MRI) after the implantation of interspinous device and the fusion of the adjacent segment. A total of 62 consecutive patients suffering L5/S1 lumbar disc herniation (LDH) with concomitant disc space narrowing or low-grade instability up to 5 mm translational slip in L5/S1 level were treated with lumbar interbody fusion (LIF) via posterior approach. Thirty-four of these patients (Coflex group) received an additional implantation of the interspinous spacer device (Coflex™) in the level L4/L5, while the rest of 28 patients (fusion group) underwent the fusion surgery alone. Clinical and radiographic examinations were performed at pre- and postoperative visits to compare the clinical outcomes and the changes of the L4/L5 vertebral disc degeneration on MRI in both Coflex and fusion group. Although both Coflex and fusion group showed improvements of the clinical outcomes assessed by the Oswestry Disability Index (ODI) after surgery, patients in Coflex group had more significant amelioration (P < 0.05) compared to fusion group. During follow up, the postoperative disc degeneration changes in Coflex group assessed by the relative signal intensity (RSI) differed from those in fusion group (P < 0.05). The supplemental implantation of Coflex™ after the fusion surgery could delay the disc degeneration of the adjacent segment.

  13. Biomechanical Analysis of the Proximal Adjacent Segment after Multilevel Instrumentation of the Thoracic Spine: Do Hooks Ease the Transition?

    PubMed Central

    Metzger, Melodie F.; Robinson, Samuel T.; Svet, Mark T.; Liu, John C.; Acosta, Frank L.

    2015-01-01

    Study Design Biomechanical cadaveric study. Objective Clinical studies indicate that using less-rigid fixation techniques in place of the standard all-pedicle screw construct when correcting for scoliosis may reduce the incidence of proximal junctional kyphosis and improve patient outcomes. The purpose of this study is to investigate whether there is a biomechanical advantage to using supralaminar hooks in place of pedicle screws at the upper-instrumented vertebrae in a multilevel thoracic construct. Methods T7–T12 spines were biomechanically tested: (1) intact; (2) following a two-level pedicles screw fusion from T9 to T11; and after proximal extension of the fusion to T8–T9 with (3) bilateral supra-laminar hooks, (4) a unilateral hook + unilateral screw hybrid, or (5) bilateral pedicle screws. Specimens were nondestructively loaded while three-dimensional kinematics and intradiscal pressure at the supra-adjacent level were recorded. Results Supra-adjacent hypermobility was reduced when bilateral hooks were used in place of pedicle screws at the upper-instrumented level, with statistically significant differences in lateral bending and torsion (p < 0.05 and p < 0.001, respectively). Disk pressures in the supra-adjacent segment were not statistically different among top-off techniques. Conclusions The use of supralaminar hooks at the top of a multilevel posterior fusion construct reduces the stress at the proximal uninstrumented motion segment. Although further data is needed to provide a definitive link to the clinical occurrence of PJK, this in vitro study demonstrates the potential benefit of “easing” the transition between the stiff instrumented spine and the flexible native spine and is the first to demonstrate these results with laminar hooks. PMID:27190735

  14. Earthquake Ground Motion for the Salt Lake City Segment of the Wasatch Fault

    NASA Astrophysics Data System (ADS)

    Liu, Q.; Archuleta, R. J.

    2009-12-01

    Approximately 80% of Utah’s 2.7 million people live within 15 miles of the Wasatch Fault. This area is one of the most hazardous places in the US that under the threat of big earthquakes (M > 7). The Salt Lake City segment of the Wasatch Fault (SLCWF) poses a serious threat to the nearby city and surrounding communities. The SLCWF is a normal fault with a dip of about 50° that forms a boundary between the Wasatch Mountains to the east and a relatively thin sedimentary basin to the west that rests on the hanging wall. Recently a 3D Wasatch Fault Community Velocity Model (WFCVM) was released for the region. To have a more accurate estimation of what the ground motion might be due to potential earthquakes, we use a finite element method (Ma & Liu, BSSA, 2006) to simulate dynamic ruptures on the fault embedded within the WFCVM. We will consider simplified heterogeneous velocity models (e.g. layered model) and compare the results with the one given by WFCVM to get a better understanding of the effects on ground motion due to velocity structure heterogeneity. Preliminary results for simple layer models over a halfspace already indicate that the ground motion in the basin, i.e., on the hanging wall, is significantly greater than the footwall. The maximum ground velocities occur over a swath whose width is comparable to depth of the basin.

  15. Conditional, Time-Dependent Probabilities for Segmented Type-A Faults in the WGCEP UCERF 2

    USGS Publications Warehouse

    Field, Edward H.; Gupta, Vipin

    2008-01-01

    This appendix presents elastic-rebound-theory (ERT) motivated time-dependent probabilities, conditioned on the date of last earthquake, for the segmented type-A fault models of the 2007 Working Group on California Earthquake Probabilities (WGCEP). These probabilities are included as one option in the WGCEP?s Uniform California Earthquake Rupture Forecast 2 (UCERF 2), with the other options being time-independent Poisson probabilities and an ?Empirical? model based on observed seismicity rate changes. A more general discussion of the pros and cons of all methods for computing time-dependent probabilities, as well as the justification of those chosen for UCERF 2, are given in the main body of this report (and the 'Empirical' model is also discussed in Appendix M). What this appendix addresses is the computation of conditional, time-dependent probabilities when both single- and multi-segment ruptures are included in the model. Computing conditional probabilities is relatively straightforward when a fault is assumed to obey strict segmentation in the sense that no multi-segment ruptures occur (e.g., WGCEP (1988, 1990) or see Field (2007) for a review of all previous WGCEPs; from here we assume basic familiarity with conditional probability calculations). However, and as we?ll see below, the calculation is not straightforward when multi-segment ruptures are included, in essence because we are attempting to apply a point-process model to a non point process. The next section gives a review and evaluation of the single- and multi-segment rupture probability-calculation methods used in the most recent statewide forecast for California (WGCEP UCERF 1; Petersen et al., 2007). We then present results for the methodology adopted here for UCERF 2. We finish with a discussion of issues and possible alternative approaches that could be explored and perhaps applied in the future. A fault-by-fault comparison of UCERF 2 probabilities with those of previous studies is given in the

  16. Particle size distributions, microstructures and chemistry of fault rocks in a shallow borehole adjacent to the San Andreas Fault near Little Rock, CA

    NASA Astrophysics Data System (ADS)

    Wechsler, N.; Chester, J. S.; Rockwell, T. K.; Ben-Zion, Y.

    2009-12-01

    In mapping the distribution of fractured crystalline rocks along the Mojave section of the San Andreas Fault (SAF), Dor et al. (2006) found that almost all rocks within 50 to 200 m from the fault are pulverized to some degree. In an effort to characterize the role of surface weathering, and quantify the mesoscale and microscale deformation of these rocks as a function of depth in the shallow subsurface environment, we have collected a nearly continuous, 42 meter-deep core from the pulverized adjacent to the main strand of the SAF near Little Rock, California. The Little Rock site is characterized by extensive outcrops of granitic rock displaying varying degrees of damage up to a few hundreds of meters from the fault’s primary active strand. The cored section primarily is composed of pulverized granites and granodiorites, and is cut by numerous mesoscopic secondary shears. Medium to coarse silt- and fine sand-size particles dominate throughout the cored section; very few micron-scale particles are observed and only minor amounts of clay weathering products are present. Mapping on optical and SEM images of core samples at various depths and magnifications defines the distribution of two main fault rock types, pulverized zones displaying primarily opening-mode fractures, and cataclastic fault zones. The pulverized regions display large host-rock crystals that are fractured to produce angular particles often ranging from 10-100 microns in diameter. The fractured parts display optical continuity and a high density of fluid inclusion trails suggesting episodes of fracture healing. The cataclastic zones are characterized by smaller (0.5-10 microns) and more rounded grains, a greater clay content, and sometimes show repeated stages of calcite cementation and shear. The distribution of pulverized particles and cataclastic zones indicate multiple fracture-healing cycles to produce an outcrop that reduces to powder when dug out with a hammer. Most samples analyzed to date

  17. Hydrothermal plumes along segments of contrasting magmatic influence, 15°20'-18°30'N, East Pacific Rise: Influence of axial faulting

    NASA Astrophysics Data System (ADS)

    Baker, Edward T.; Cormier, Marie-Helene; Langmuir, Charles H.; Zavala, Karina

    2001-09-01

    Vertical profiles of light backscattering and temperature recorded on 133 rock cores and dredge hauls between the Orozco and Rivera transform faults on the East Pacific Rise (EPR) (15°20'-18°30'N) provide an opportunity to compare the hydrothermal environment of three adjacent but distinctly different segments that span the maximum range of axial cross section at a relatively constant spreading rate. Contrary to predictions based on data from other Pacific ridges, hydrothermal plumes over the inflated 16°N segment were less extensive and weaker than along the narrower, rifted 17°N segment. Remarkably, the 17°N segment has a plume incidence equal to the mean of superfast spreading segments from the southern EPR. The data suggest that the local permeability environment in this region controls the expression of hydrothermal activity in the water column. The 16°N segment, which has little or no indication of faulting, may have its hydrothermal activity presently suppressed by widespread volcanic flows that act as an impermeable cap over much of the segment. Activity on the 17°N segment may be tectonically enhanced, with hydrothermal fluids circulating through deep faults to a cracking front. Within each segment, intense hydrothermal plumes characteristic of focused discharge seem associated with clearly rifted areas, while weaker water column signals characteristic of diffuse discharge are associated with unrifted portions of the ridge axis that appear dominated by magmatism. Previous studies at intermediate- to-superfast spreading ridges have emphasized a positive correlation between local magmatic budget and hydrothermal activity. Our data suggest, however, that even at fast rates local tectonics can control the extent and nature of hydrothermal activity, as documented for several sites on the slow-spreading Mid-Atlantic Ridge. Despite the segment-scale incongruity between hydrothermal activity and magmatic budget, the fraction of total ridge length between 15

  18. Apparatus for impingement cooling a side wall adjacent an undercut region of a turbine nozzle segment

    DOEpatents

    Burdgick, Steven Sebastian

    2002-01-01

    A gas turbine nozzle segment has outer and inner bands and vanes therebetween. Each band includes a side wall, a cover and an impingement plate between the cover and nozzle wall defining two cavities on opposite sides of the impingement plate. Cooling steam is supplied to one cavity for flow through apertures of the impingement plate to cool the nozzle wall. The side wall of the band and inturned flange define with the nozzle wall an undercut region. Slots are formed through the inturned flange along the nozzle side wall. A plate having through-apertures extending between opposite edges thereof is disposed in each slot, the slots and plates being angled such that the cooling medium exiting the apertures in the second cavity lie close to the side wall for focusing and targeting cooling medium onto the side wall.

  19. Posterior lumbar dynamic stabilization instead of arthrodesis for symptomatic adjacent-segment degenerative stenosis: description of a novel technique.

    PubMed

    Mashaly, Hazem; Paschel, Erin E; Khattar, Nicolas K; Goldschmidt, Ezequiel; Gerszten, Peter C

    2016-01-01

    OBJECTIVE The development of symptomatic adjacent-segment disease (ASD) is a well-recognized consequence of lumbar fusion surgery. Extension of a fusion to a diseased segment may only lead to subsequent adjacent-segment degeneration. The authors report the use of a novel technique that uses dynamic stabilization instead of arthrodesis for the surgical treatment of symptomatic ASD following a prior lumbar instrumented fusion. METHODS A cohort of 28 consecutive patients was evaluated who developed symptomatic stenosis immediately adjacent to a previous lumbar instrumented fusion. All patients had symptoms of neurogenic claudication refractory to nonsurgical treatment and were surgically treated with decompression and dynamic stabilization instead of extending the fusion construct using a posterior lumbar dynamic stabilization system. Preoperative symptoms, visual analog scale (VAS) pain scores, and perioperative complications were recorded. Clinical outcome was gauged by comparing VAS scores prior to surgery and at the time of last follow-up. RESULTS The mean follow-up duration was 52 months (range 17-94 months). The mean interval from the time of primary fusion surgery to the dynamic stabilization surgery was 40 months (range 10-96 months). The mean patient age was 51 years (range 29-76 years). There were 19 (68%) men and 9 (32%) women. Twenty-three patients (82%) presented with low-back pain at time of surgery, whereas 24 patients (86%) presented with lower-extremity symptoms only. Twenty-four patients (86%) underwent operations that were performed using single-level dynamic stabilization, 3 patients (11%) were treated at 2 levels, and 1 patient underwent 3-level decompression and dynamic stabilization. The most commonly affected and treated level (46%) was L3-4. The mean preoperative VAS pain score was 8, whereas the mean postoperative score was 3. No patient required surgery for symptomatic degeneration rostral to the level of dynamic stabilization during the

  20. Posterior lumbar dynamic stabilization instead of arthrodesis for symptomatic adjacent-segment degenerative stenosis: description of a novel technique.

    PubMed

    Mashaly, Hazem; Paschel, Erin E; Khattar, Nicolas K; Goldschmidt, Ezequiel; Gerszten, Peter C

    2016-01-01

    OBJECTIVE The development of symptomatic adjacent-segment disease (ASD) is a well-recognized consequence of lumbar fusion surgery. Extension of a fusion to a diseased segment may only lead to subsequent adjacent-segment degeneration. The authors report the use of a novel technique that uses dynamic stabilization instead of arthrodesis for the surgical treatment of symptomatic ASD following a prior lumbar instrumented fusion. METHODS A cohort of 28 consecutive patients was evaluated who developed symptomatic stenosis immediately adjacent to a previous lumbar instrumented fusion. All patients had symptoms of neurogenic claudication refractory to nonsurgical treatment and were surgically treated with decompression and dynamic stabilization instead of extending the fusion construct using a posterior lumbar dynamic stabilization system. Preoperative symptoms, visual analog scale (VAS) pain scores, and perioperative complications were recorded. Clinical outcome was gauged by comparing VAS scores prior to surgery and at the time of last follow-up. RESULTS The mean follow-up duration was 52 months (range 17-94 months). The mean interval from the time of primary fusion surgery to the dynamic stabilization surgery was 40 months (range 10-96 months). The mean patient age was 51 years (range 29-76 years). There were 19 (68%) men and 9 (32%) women. Twenty-three patients (82%) presented with low-back pain at time of surgery, whereas 24 patients (86%) presented with lower-extremity symptoms only. Twenty-four patients (86%) underwent operations that were performed using single-level dynamic stabilization, 3 patients (11%) were treated at 2 levels, and 1 patient underwent 3-level decompression and dynamic stabilization. The most commonly affected and treated level (46%) was L3-4. The mean preoperative VAS pain score was 8, whereas the mean postoperative score was 3. No patient required surgery for symptomatic degeneration rostral to the level of dynamic stabilization during the

  1. Imaging heterogeneity of the crust adjacent to the Dead Sea fault using ambient seismic noise tomography

    NASA Astrophysics Data System (ADS)

    Pinsky, Vladimir; Meirova, Tatiana; Levshin, Anatoli; Hofstetter, Abraham; Kraeva, Nadezda; Barmin, Mikhail

    2013-04-01

    For the purpose of studying the Earth's crust by means of tomography, we investigated cross-correlation functions emerging from long-term observations of propagating ambient seismic noise at pairs of broadband stations in Israel and Jordan. The data was provided by the eight permanent broadband stations of the Israel Seismic Network evenly distributed over Israel and the 30 stations of the DESERT2000 experiment distributed across the Arava Fault (South of the Dead Sea basin). To eliminate the influence of earthquakes and explosions, we have applied the methodology of Bensen et al. (Geophys J Int 169:1239-1260, 2007), including bandpass filtering and amplitude normalization in time and frequency domain. The cross-correlation functions estimated from continuous recordings of a few months were used to extract Rayleigh waves group velocity dispersion curves using automatic version of the frequency-time analysis procedure. Subsequently, these curves have been converted into the Rayleigh wave group velocity maps in the period range 5-20 s and S waves velocity maps in the depth range 5-15 km. In these maps, four velocity anomalies are prominent. Two of them are outlined by the previous reflection-refraction profiles and body wave tomography studies, i.e. a low velocity anomaly corresponds to the area of the extremely deep (down to 14 km) sedimentary infill in the Southern Dead Sea Basin and a high velocity anomaly in the Southern Jordan corresponds to the area of the Precambrian crystalline rocks of the Nubian Shield on the flanks of the Red Sea. The two other anomalies have not been reported before - the high velocity zone close to the Beersheba city and the low velocity anomaly in the region of Samaria-Carmel mountains - Southern Galilee. They have relatively low resolution and hence need further investigations for approving and contouring. The highest contrast between the average Rayleigh wave group velocity (2.7 km/s) and the anomalies is 10-13 %, comparable, however

  2. Deep crustal heterogeneity along and around the San Andreas fault system in central California and its relation to the segmentation

    NASA Astrophysics Data System (ADS)

    Nishigami, Kin'ya

    2000-04-01

    The three-dimensional distribution of scatterers in the crust along and around the San Andreas fault system in central California is estimated using an inversion analysis of coda envelopes from local earthquakes. I analyzed 3801 wave traces from 157 events recorded at 140 stations of the Northern California Seismic Network. The resulting scatterer distribution shows a correlation with the San Gregorio, San Andreas, Hayward, and Calaveras faults. These faults seem to be almost vertical from the surface to ˜15 km depth. Some of the other scatterers are estimated to be at shallow depths, 0-5 km, below the Diablo Range, and these may be interpreted as being generated by topographic roughness. The depth distribution of scatterers shows relatively stronger scattering in the lower crust, at ˜15-25 km depth, especially between the San Andreas fault and the Hayward-Calaveras faults. This suggests a subhorizontal detachment structure connecting these two faults in the lower crust. Several clusters of scatterers are located along the San Andreas fault at intervals of ˜20-30 km from south of San Francisco to the intersection with the Calaveras fault. This part of the San Andreas fault appears to consist of partially locked segments, also ˜20-30 km long, which rupture during M6-7 events, and segment boundaries characterized by stronger scattering and stationary microseismicity. The segment boundaries delineated by the present analysis correspond with those estimated from the slip distribution of the great 1906 San Francisco earthquake, and from the fault geometry as reported by the Working Group on California Earthquake Probabilities [1990], although the segment boundaries along the San Andreas fault in and around the San Francisco Bay area are still uncertain.

  3. Investigating the Creeping Segment of the San Andreas Fault using InSAR time series analysis

    NASA Astrophysics Data System (ADS)

    Rolandone, Frederique; Ryder, Isabelle; Agram, Piyush S.; Burgmann, Roland; Nadeau, Robert M.

    2010-05-01

    We exploit the advanced Interferometric Synthetic Aperture Radar (InSAR) technique referred to as the Small BAseline Subset (SBAS) algorithm to analyze the creeping section of the San Andreas Fault in Central California. Various geodetic creep rate measurements along the Central San Andreas Fault (CSAF) have been made since 1969 including creepmeters, alignment arrays, geodolite, and GPS. They show that horizontal surface displacements increase from a few mm/yr at either end to a maximum of up to ~34 mm/yr in the central portion. They also indicate some discrepancies in rate estimates, with the range being as high as 10 mm/yr at some places along the fault. This variation is thought to be a result of the different geodetic techniques used and of measurements being made at variable distances from the fault. An interferometric stack of 12 interferograms for the period 1992-2001 shows the spatial variation of creep that occurs within a narrow (<2 km) zone close to the fault trace. The creep rate varies spatially along the fault but also in time. Aseismic slip on the CSAF shows several kinds of time dependence. Shallow slip, as measured by surface measurements across the narrow creeping zone, occurs partly as ongoing steady creep, along with brief episodes with slip from mm to cm. Creep rates along the San Juan Bautista segment increased after the 1989 Loma Prieta earthquake and slow slip transients of varying duration and magnitude occurred in both transition segments The main focus of this work is to use the SBAS technique to identify spatial and temporal variations of creep on the CSAF. We will present time series of line-of-sight (LOS) displacements derived from SAR data acquired by the ASAR instrument, on board the ENVISAT satellite, between 2003 and 2009. For each coherent pixel of the radar images we compute time-dependent surface displacements as well as the average LOS deformation rate. We compare our results with characteristic repeating microearthquakes that

  4. Geomorphic evidence of unrecognized Balapur fault segment in the southwest Kashmir basin of northwest Himalayas

    NASA Astrophysics Data System (ADS)

    Ahmad, Shabir; Alam, Akhtar; Ahmad, Bashir; Bhat, M. I.; Sultan Bhat, M.

    2015-12-01

    The Balapur fault (BF) is a high angle thrust fault (reverse), dipping ~ 60° NE, with an established length of ~ 40 km striking NW-SE of the Kashmir basin. However, geomorphic traces suggest that the strike of the BF propagates beyond what has been documented previously. The present investigation aims to identify the unrecognized segment of the BF in the SW of the Kashmir basin using hypsometric variability in longitudinal profiles (knickpoints/zones), followed by validation through stream gradient index (SL) calculations of the rivers draining the area. The longitudinal profiles of all the streams indicate prominent and consistent anomalies in the upper and mid-reaches even on the coarse resolution data (Survey of India topographic maps - 1:50,000/40 m, DEM-SRTM 90 m). The profile anomalies in the upper reaches (hard rock zone) of the streams may be attributed to lithological contacts, i.e., Panjal trap agglomeratic slate-shale-limestone. However, the river profile convex segments and course deflection specifically in the mid-reaches (soft rock zone) are most likely associated with recent tectonic activity. Geomorphic signatures suggest that these anomalies coincide with the strike of the recognized segment of the BF. Moreover, the SL values of each stream express a clear agreement with the anomalies shown by the long profiles of the rivers. Hence, we infer that the strike of the BF extends for a significant distance (~ 95 km) over the northeastern flank of the Pir Panjal range in the NW-SE direction.

  5. Shallow subsurface structure of the Wasatch fault, Provo segment, Utah, from integrated compressional and shear-wave seismic reflection profiles with implications for fault structure and development

    USGS Publications Warehouse

    McBride, J.H.; Stephenson, W.J.; Williams, R.A.; Odum, J.K.; Worley, D.M.; South, J.V.; Brinkerhoff, A.R.; Keach, R.W.; Okojie-Ayoro, A. O.

    2010-01-01

    Integrated vibroseis compressional and experimental hammer-source, shear-wave, seismic reflection profiles across the Provo segment of the Wasatch fault zone in Utah reveal near-surface and shallow bedrock structures caused by geologically recent deformation. Combining information from the seismic surveys, geologic mapping, terrain analysis, and previous seismic first-arrival modeling provides a well-constrained cross section of the upper ~500 m of the subsurface. Faults are mapped from the surface, through shallow, poorly consolidated deltaic sediments, and cutting through a rigid bedrock surface. The new seismic data are used to test hypotheses on changing fault orientation with depth, the number of subsidiary faults within the fault zone and the width of the fault zone, and the utility of integrating separate elastic methods to provide information on a complex structural zone. Although previous surface mapping has indicated only a few faults, the seismic section shows a wider and more complex deformation zone with both synthetic and antithetic normal faults. Our study demonstrates the usefulness of a combined shallow and deeper penetrating geophysical survey, integrated with detailed geologic mapping to constrain subsurface fault structure. Due to the complexity of the fault zone, accurate seismic velocity information is essential and was obtained from a first-break tomography model. The new constraints on fault geometry can be used to refine estimates of vertical versus lateral tectonic movements and to improve seismic hazard assessment along the Wasatch fault through an urban area. We suggest that earthquake-hazard assessments made without seismic reflection imaging may be biased by the previous mapping of too few faults. ?? 2010 Geological Society of America.

  6. Effect of distributed inelastic deformation on fault slip profiles and fault interaction under mid-crustal conditions

    NASA Astrophysics Data System (ADS)

    Nevitt, J. M.; Pollard, D. D.

    2015-12-01

    Under mid-crustal conditions, faults commonly are associated with distributed inelastic deformation (i.e., ductile fabrics). The effect of such inelastic deformation on fault slip profiles and fault interaction remains poorly understood, though it likely plays a significant role in the earthquake cycle. We have investigated meter-scale strike-slip faults exhumed from ~10 km depth in the Lake Edison granodiorite (Sierra Nevada, CA). These faults are characterized by slip-to-length ratios and slip gradients near fault tips that greatly exceed what is measured for faults in the brittle upper crust, or produced by linear elastic models. Using Abaqus, we construct elastoplastic finite element models to evaluate the impact of off-fault plasticity on the resulting slip profiles for both continuous and discontinuous faults. Elastoplastic models show that plastic strain near fault tips effectively lengthens faults, allowing for greater overall slip and increased slip gradients near fault tips. In the field, regions adjacent to fault tips contain mylonitized granodiorite and ductilely sheared dikes and schlieren, consistent with the model results. In addition, distributed plastic strain facilitates slip transfer between echelon fault segments, particularly for contractional step geometries. Relative to an isolated fault, fault segments adjacent to contractional steps are asymmetric, with the maximum slip shifted in the direction of the step. Immediately adjacent to the contractional step, fault slip is significantly reduced because shear offset is accommodated by distributed plastic shearing within the step, rather than by discrete slip on the faults. Although slip is locally reduced on each fault segment directly adjacent to a contractional step, overall slip transfer between discontinuous fault segments is most efficient for this step geometry. That is, faults segmented by contractional steps produce greater maximum slip than do those separated by extensional steps

  7. The regional structural setting of the 2008 Wells earthquake and Town Creek Flat Basin: implications for the Wells earthquake fault and adjacent structures

    USGS Publications Warehouse

    Henry, Christopher S.; Colgan, Joseph P.

    2011-01-01

    The 2008 Wells earthquake occurred on a northeast-striking, southeast-dipping fault that is clearly delineated by the aftershock swarm to a depth of 10-12 km below sea level. However, Cenozoic rocks and structures around Wells primarily record east-west extension along north- to north-northeast-striking, west-dipping normal faults that formed during the middle Miocene. These faults are responsible for the strong eastward tilt of most basins and ranges in the area, including the Town Creek Flat basin (the location of the earthquake) and the adjacent Snake Mountains and western Windermere Hills. These older west-dipping faults are locally overprinted by a younger generation of east-dipping, high-angle normal faults that formed as early as the late Miocene and have remained active into the Quaternary. The most prominent of these east-dipping faults is the set of en-échelon, north-striking faults that bounds the east sides of the Ruby Mountains, East Humboldt Range, and Clover Hill (about 5 km southwest of Wells). The northeastern-most of these faults, the Clover Hill fault, projects northward along strike toward the Snake Mountains and the approximately located surface projection of the Wells earthquake fault as defined by aftershock locations. The Clover Hill fault also projects toward a previously unrecognized, east-facing Quaternary fault scarp and line of springs that appear to mark a significant east-dipping normal fault along the western edge of Town Creek Flat. Both western and eastern projections may be northern continuations of the Clover Hill fault. The Wells earthquake occurred along this east-dipping fault system. Two possible alternatives to rupture of a northern continuation of the Clover Hill fault are that the earthquake fault (1) is antithetic to an active west-dipping fault or (2) reactivated a Mesozoic thrust fault that dips east as a result of tilting by the west-dipping faults along the west side of the Snake Mountains. Both alternatives are

  8. Thermoluminescence dating of fault-scarp-derived colluvium: Deciphering the timing of paleoearthquakes on the Weber segment of the Wasatch fault zone, north central Utah

    SciTech Connect

    Forman, S.L. ); Nelson, A.R. ); McCalpin J.P. )

    1991-01-10

    The timing of middle to late Holocene faulting on the Weber segment of the Wasatch fault zone, Utah, is constrained by thermoluminescence (TL) and radiocarbon age estimates on fine-grained, fault-related colluvial sediments. The stratigraphy in two trenches excavated across fault scarps is characterized by a stack of three colluvial wedges, deposited in response to three separate faulting events, the oldest of which buried a soil developed on a middle Holocene debris flow. Thermoluminescence age estimates by the partial and total bleach methods and the regeneration method on fine-grained colluvium from the trenches agree within 1 sigma and are concordant with the radiocarbon chronology. A synthesis of the TL and {sup 14}C age estimates indicate that these three faulting events occurred sometime between 4,500 and 3,500, between 3,200 and 2,500, and between 1,400 and 1,000 years ago. Detailed investigation of a sequence of fine-grained, scarp-derived distal colluvium shows that much of the sediment was deposited during <600-year intervals immediately after faulting. The sedimentation rate of colluvium is inferred to increase shortly after faulting, and TL dating of these sediments provides additional information to constrain the timing of faulting events.

  9. Enhancement of Lumbar Fusion and Alleviation of Adjacent Segment Disc Degeneration by Intermittent PTH(1-34) in Ovariectomized Rats.

    PubMed

    Zhou, Zhuang; Tian, Fa-Ming; Gou, Yu; Wang, Peng; Zhang, Heng; Song, Hui-Ping; Shen, Yong; Zhang, Ying-Ze; Zhang, Liu

    2016-04-01

    Osteoporosis, which is prevalent in postmenopausal or aged populations, is thought to be a contributing factor to adjacent segment disc degeneration (ASDD), and the incidence and extent of ASDD may be augmented by osteopenia. Parathyroid hormone (PTH) (1-34) has already been shown to be beneficial in osteoporosis, lumbar fusion and matrix homeostasis of intervertebral discs. However, whether PTH(1-34) has a reversing or retarding effect on ASDD in osteopenia has not been confirmed. In the present study, we evaluated the effects of intermittent PTH(1-34) on ASDD in an ovariectomized (OVX) rat model. One hundred 3-month-old female Sprague-Dawley rats underwent L4 -L5 posterolateral lumbar fusion (PLF) with spinous-process wire fixation 4 weeks after OVX surgery. Control groups were established accordingly. PTH(1-34) was intermittently administered immediately after PLF surgery and lasted for 8 weeks using the following groups (n = 20) (V = vehicle): Sham+V, OVX+V, Sham+PLF+V, OVX+PLF+V, OVX+PLF+PTH. The fused segments showed clear evidence of eliminated motion on the fusion-segment based on manual palpation. Greater new bone formation in histology was observed in PTH-treated animals compared to the control group. The extent of ASDD was significantly increased by ovariotomy. Intermittent PTH(1-34) significantly alleviated ASDD by preserving disc height, microvessel density, relative area of vascular buds, endplate thickness and the relative area of endplate calcification. Moreover, protein expression results showed that PTH(1-34) not only inhibited matrix degradation by decreasing MMP-13, ADAMTS-4 and Col-I, but also promote matrix synthesis by increasing Col-II and Aggrecan. In conclusion, PTH(1-34), which effectively improves lumbar fusion and alleviates ASDD in ovariectomized rats, may be a potential candidate to ameliorate the prognosis of lumbar fusion in osteopenia.

  10. The Efficacy of Lumbar Hybrid Stabilization Using the DIAM™ to Delay Adjacent Segment Degeneration: An Intervention Comparison Study With a Minimum Two-Year Follow-up.

    PubMed

    Lee, Chang-Hyun; Hyun, Seung-Jae; Kim, Ki-Jeong; Jahng, Tae-Ahn; Yoon, Sang Hoon; Kim, Hyun-Jib

    2013-04-29

    BACKGROUND:: Although posterior lumbar interbody fusion (PLIF) has a successful fusion rate, the long-term outcome of PLIF is occasionally below expectations because of adjacent segment degeneration (ASD). OBJECTIVE:: To evaluate the ability of hybrid stabilization using DIAM(Device for Interspinous Assisted Motion) to delay ASD. METHODS:: An intervention comparison study of 75 patients (hybrid, 25; PLIF, 50) was performed. The indications for hybrid stabilization were facet joint degeneration, Pfirrmann grade II-III, and stenosis at the rostral adjacent segment. The PLIF group consisted of patients matched for age, gender, and fusion. The hybrid stabilization procedure included traditional PLIF and DIAM installation at a superior adjacent segment. The outcomes were analyzed using linear mixed model analysis. Conditional logistic regression was performed to calculate the odds ratio for the association of surgical methods. RESULTS:: The hybrid group (24%) revealed fewer ASDs than the PLIF group (48%). Among ASDs, spondylolisthesis occurred more frequently in the PLIF group than the hybrid group. Hybrid surgery was significantly associated with ASD; the odds ratio for hybrid surgery was 0.28 when compared to PLIF. Foraminal height of the PLIF group decreased more than the hybrid group (P=.01). Segmental mobility showed a greater increase in the PLIF group than the hybrid group (P=.04). However, the clinical outcomes did not show significant differences between the groups. CONCLUSION:: Hybrid stabilization using DIAM and pedicle screws can be used for patients with facet degeneration at adjacent segments but should be further investigated.

  11. Seismic and Aseismic Moment Budget and Implication for the Seismic Potential of the Parkield Segment of the San Andreas Fault

    NASA Astrophysics Data System (ADS)

    Michel, S. G. R. M.

    2015-12-01

    This study explores methods to assess the seismic potential of a fault based on geodetic measurements, geological information of fault slip rate and seismicity data. The methods are applied to the Parkfield's section along the San Andreas Fault at the transition zone between the SAF creeping segment in the North and the locked section to the south, where a Mw~6 earthquake has occurred every 24.5 years on average since the M7.7 Fort Tejon event in 1857. We compare the moment released by all the known earthquakes and associated postseismic deformation with the moment deficit accumulated during the interseismic period. We find that the recurrence of Mw6 earthquakes is insufficient to close the slip budget and that larger events are probably needed. We will discuss and evaluate various possible scenarios which might account for the residual moment deficit and implications of the possible magnitude and return period of Mw6 earthquakes on that fault segment.

  12. Slip History of the 1944 Rupture Segment on North Anatolia Fault Near Gerede, Turkey: Constraints on Earthquake Recurrence Models

    NASA Astrophysics Data System (ADS)

    Okumura, K.; Rockwell, T. K.; Akciz, S. O.; Wechsler, N.; Aksoy, E. M.; Ishimura, D.

    2009-12-01

    Completeness of historic earthquake catalogs must be examined by geologic records, though the geologic records are not always more complete and precise than historic records. The historic records on large earthquakes from the North Anatolian fault are tested in trenches on the 1944 segment. Previous results indicated 3 historic and 1 geologic events in past 1000 years with characteristic ~ 5 m slip and quasi-periodic recurrence every 200-280 years. The one geologic event without historic information is critical to know the recurrence behavior of the fault and catalog evaluation. We excavated seven new trenches at the Ardicli paleoseismic site, located about 15 km east of Gerede, to resolve displacement on a Byzantine-aged channel and the timing of the offsets. The channel appears to have been excavated to drain the site and allow mining of clay for making bricks and tiles: a kiln was found adjacent to the channel. The V-shaped channel thalweg is offset 13.5+1.5 m, and based on many cross-fault trenches, represents slip in the past three surface ruptures. Dating of the channel is on pine cones, wood and charcoal that are incorporated into the channel deposits and in the stratified sediments into which the channel is cut: current dating suggests that this channel dates to the 9th-11th century AD. If confirmed with additional dates, the surface rupture that initially offset the channel likely corresponds to the historically-reported earthquake in AD 1035. The surface geomorphology records displacement from two more recent events. The 1944 surface rupture in this region produced 4-5 m of slip based on offset field boundaries and small channels. Older fluvial channels and rills in this area show about 10 m of displacement. We dated the fill from a 10 m offset channel, and place the penultimate event as younger than about AD 1650, which must correspond to the well-documented earthquake in 1668. From our previously reported work, we resolved 22-26 m of displacement for

  13. Structural and Morpho-Tectonic Features of the Golbasi-Turkoglu Segment of East Anatolian Fault Zone

    NASA Astrophysics Data System (ADS)

    Ozsarac, V.; Tekin, B. M.; Kuterdem, N. K.

    2009-04-01

    East Anatolian Fault Zone (EAFZ) is a 580km. long left lateral active strike slip fault and the width of deformation zone is approximately 30km. Six different fault segments with length varying between 50km to 145km. constitutes the EAFZ. Historical and instrumental earthquake data reveals that, Golbasi-Turoglu segment of EAFZ is seismically dormant since last 500 years and also this segment is accepted as a seismic gap on EAFZ which has a potential to pose a seismic risk on nearby settlement areas. This study aims to determine the main active faults in the study area and determination of fault associated land surfaces by using geographic information system tools (GIS), remote sensing analysis and field observations. The study is conducted in two phases. The initial phase can be defined as office work where extensive morphological analysis and data preparation were performed by using GIS software. The second and the last phase of the study consisted of extensive field surveys, data verification. In the first part of the study a 1/25.000 scaled digital elevation models and derived morphological maps and Landsat ETM and SPOT 5 PAN images were analyzed for the study area. Lineaments were also extracted from DEMs and satellite images and analyzed. Those analysis were correlated with field observations and Analgyph images of the fault zone. Main strike slip fault related landforms like alluvial fans, river offsets and landslides were determined from morphological analysis. As the result of this study The active faults of the study area were delineated and mapped. This data is also used in the site selection of trenches for paleoseismological studies. Further steps will be the paleoseismological studies which will put definite outcomes for the seismic hazard evaluation of this segment and nearby region. It is noteworthy that GIS and remote sensing applications in geology, especially in tectonics and geomorphology, proposes practical practical and valuable solutions in

  14. Comparison of percutaneous endoscopic lumbar discectomy and open lumbar surgery for adjacent segment degeneration and recurrent disc herniation.

    PubMed

    Chen, Huan-Chieh; Lee, Chih-Hsun; Wei, Li; Lui, Tai-Ngar; Lin, Tien-Jen

    2015-01-01

    Objective. The goal of the present study was to examine the clinical results of percutaneous endoscopic lumbar discectomy (PELD) and open lumbar surgery for patients with adjacent segment degeneration (ASD) and recurrence of disc herniation. Methods. From December 2011 to November 2013, we collected forty-three patients who underwent repeated lumbar surgery. These patients, either received PELD (18 patients) or repeated open lumbar surgery (25 patients), due to ASD or recurrence of disc herniation at L3-4, L4-5, or L5-S1 level, were assigned to different groups according to the surgical approaches. Clinical data were assessed and compared. Results. Mean blood loss was significantly less in the PELD group as compared to the open lumbar surgery group (P < 0.0001). Hospital stay and mean operating time were shorter significantly in the PELD group as compared to the open lumbar surgery group (P < 0.0001). Immediate postoperative pain improvement in VAS was 3.5 in the PELD group and -0.56 in the open lumbar surgery group (P < 0.0001). Conclusion. For ASD and recurrent lumbar disc herniation, PELD had more advantages over open lumbar surgery in terms of reduced blood loss, shorter hospital stay, operating time, fewer complications, and less postoperative discomfort.

  15. Geomorphic Evolution and Slip rate Measurements of the Noushki Segment , Chaman Fault Zone, Pakistan

    NASA Astrophysics Data System (ADS)

    Abubakar, Y.; Khan, S. D.; Owen, L. A.; Khan, A.

    2012-12-01

    The Nushki segment of the Chaman fault system is unique in its nature as it records both the imprints of oblique convergence along the western Indian Plate boundary as well as the deformation along the Makran subduction zone. The left-lateral Chaman transform zone has evolved from a subduction zone along the Arabian-Eurasian collision complex to a strike-slip fault system since the collision of the Indian Plate with the Eurasia. The geodetically and geologically constrained displacement rates along the Chaman fault varies from about 18 mm/yr to about 35 mm/yr respectively throughout its total length of ~ 860 km. Two major hypothesis has been proposed by workers for these variations; i) Variations in rates of elastic strain accumulation along the plate boundary and, ii) strain partitioning along the plate boundary. Morphotectonic analysis is a very useful tool in investigations of spatial variations in tectonic activities both regionally and locally. This work uses morphotectonic analysis to investigate the degree of variations in active tectonic deformation, which can be directly related to elastic strain accumulation and other kinematics in the western boundary of the plate margin. Geomorphic mapping was carried out using remotely sensed data. ASTER and RADAR data were used in establishing Quaternary stratigraphy and measurement of geomorphic indices such as stream length gradient index, valley floor width to height ratio and, river/stream longitudinal profile within the study area. High resolution satellite images (e.g., IKONOS imagery) and 30m ASTER DEMs were employed to measure displacement recorded by landforms along individual strands of the fault. Results from geomorphic analysis shows three distinct levels of tectonic deformation. Areas showing high levels of tectonic deformation are characterized by displaced fan surfaces, deflected streams and beheaded streams. Terrestrial Cosmogenic nuclide surface exposure dating of the displaced landforms is being

  16. Late Holocene Paleoseismic Timing and Slip History Along the Missyaf Segment of the Dead Sea Fault in Syria

    NASA Astrophysics Data System (ADS)

    Meghraoui, M.; Gomez, F.; Sbeinati, R.; Van der Woerd, J.; Mouty, M.; Hijazi, F.; Darkal, A.; Darawcheh, R.; Radwan, Y.; Al-Najjar, H.; Layous, I.; Al-Ghazzi, R.; Barazangi, M.

    2001-12-01

    We investigate the timing of Holocene earthquakes and related slip rate along the main segment of the Dead Sea fault south of the Ghab pull-apart basin in western Syria. The 60-70 km long Missyaf segment consists of a single fault branch of the north-south trending left-lateral fault at the plate boundary between Africa and Arabia. The late Quaternary tectonic activity along the fault is characterized by (1) deflected streams with consistent left-lateral displacements of different sizes (50 to 300 m), and (2) evidence of large shutter-ridge structures and small pull-apart basins. Microtopographic surveys and trenching across the fault at two sites document the size and timing of paleoseismic events and the related faulting behavior. Near El Harif village, the fault cut across a Roman aqueduct (younger than 22 AD) and induces 10.5 ±0.1 m of left-lateral displacement. Nearby trench-excavations and test pits exhibit the fault with the shear zone affecting a succession of young alluvial deposits of a terrace meander. Radiocarbon dating of the faulting events with vertical displacements reveal the occurrence of a large seismic event prior to 408-380 BC, a penultimate event between 22 - 979 AD and the most recent event between 979 - 1255 AD. The two most recent events being most likely responsible for the Roman aqueduct total displacement, it implies an average coseismic left-lateral movement of 5 m and a slip rate of about 5 mm/yr. The correlation with the historical seismicity catalogue suggests that the most recent faulting event may correspond to the well documented large earthquake of 1170 AD.

  17. Late Holocene Paleoseismic Timing and Slip Rate Along The Missyaf Segment of The Dead Sea Fault In Syria

    NASA Astrophysics Data System (ADS)

    Meghraoui, M.; Gomez, F.; Sbeinati, R.; van der Woerd, J.; Mouty, M.; Darkal, A.; Darawcheh, R.; Radwan, Y.; Al-Ghazzi, R.; Barazangi, M.

    We investigate the timing of Holocene earthquakes and related slip rate along the main segment of the Dead Sea fault south of the Ghab pull-apart basin in western Syria. The 60-70 km long Missyaf segment consists of a single fault branch of the north-south trending left-lateral fault at the plate boundary between Africa and Arabia. The late Quaternary tectonic activity along the fault is characterized by (1) deflected streams with consistent left-lateral displacements of different sizes (50 to 300 m), and (2) ev- idence of large shutter-ridge structures and small pull-apart basins. Microtopographic surveys and trenching across the fault at two sites document the size and timing of paleoseismic events and the related faulting behaviour. Near El Harif village, the fault cut across a Roman aqueduct (younger than 22 AD) and induces 13.6 s0.1 m of left-´ lateral displacement. Nearby trench-excavations and test pits exhibit the fault with the shear zone affecting a succession of young alluvial deposits of a terrace meander. First radiocarbon dating of the faulting events with vertical displacements reveal the occur- rence of a large seismic event prior to 348 BC - 810 BC, a penultimate event between 650 - 1152 AD and the most recent event between 979 - 1255 AD. The two most re- cent events being most likely responsible for the Roman aqueduct total displacement, it implies a coseismic left-lateral movement of 6.8 m per event at this location and a slip rate of about 6 - 7 mm/yr for the last 2000 years. The correlation with the histor- ical seismicity catalogue suggests that the most recent faulting event may correspond to the well documented large earthquake of 1170 AD for which we estimate Mw = 7.3 - 7.5.

  18. Determination of the biomechanical effect of an interspinous process device on implanted and adjacent lumbar spinal segments using a hybrid testing protocol: a finite-element study.

    PubMed

    Erbulut, Deniz U; Zafarparandeh, Iman; Hassan, Chaudhry R; Lazoglu, Ismail; Ozer, Ali F

    2015-08-01

    OBJECT The authors evaluated the biomechanical effects of an interspinous process (ISP) device on kinematics and load sharing at the implanted and adjacent segments. METHODS A 3D finite-element (FE) model of the lumbar spine (L1-5) was developed and validated through comparison with published in vitro study data. Specifically, validation was achieved by a flexible (load-control) approach in 3 main planes under a pure moment of 10 Nm and a compressive follower load of 400 N. The ISP device was inserted between the L-3 and L-4 processes. Intact and implanted cases were simulated using the hybrid protocol in all motion directions. The resultant motion, facet load, and intradiscal pressure after implantation were investigated at the index and adjacent levels. In addition, stress at the bone-implant interface was predicted. RESULTS The hybrid approach, shown to be appropriate for adjacent-level investigations, predicted that the ISP device would decrease the range of motion, facet load, and intradiscal pressure at the index level relative to the corresponding values for the intact spine in extension. Specifically, the intradiscal pressure induced after implantation at adjacent segments increased by 39.7% and by 6.6% at L2-3 and L4-5, respectively. Similarly, facet loads at adjacent segments after implantation increased up to 60% relative to the loads in the intact case. Further, the stress at the bone-implant interface increased significantly. The influence of the ISP device on load sharing parameters in motion directions other than extension was negligible. CONCLUSIONS Although ISP devices apply a distraction force on the processes and prevent further extension of the index segment, their implantation may cause changes in biomechanical parameters such as facet load, intradiscal pressure, and range of motion at adjacent levels in extension.

  19. Evaluation of the Long-Term Segmentation of the Wasatch Fault Footwall Using (U-Th)/He Thermochronometry

    NASA Astrophysics Data System (ADS)

    Taylor, A. R.; Armstrong, P. A.; Farley, K. A.

    2001-12-01

    The Wasatch fault zone (WFZ) is a 350-km-long normal fault system that is separated into ten segments based on its surface fault trace and topographic salients in the footwall Wasatch Mountains. The presence of the topographic salients, E-W striking fault zones that cut across the Wasatch, and apparent changes in depth of exposure of footwall rocks at the segment boundaries suggest these boundaries partition long-term footwall uplift and exhumation between the segments. To determine low-temperature ( ~65° C) cooling ages and infer exhumation rates within and between footwall segments, we measured multiple, single-grain laser (U-Th)/He ages on 11 footwall samples collected from the five central segments at a common elevation ( ~1500 m) along the range front. Pooled ages from this study average 5.3 +/-1.2 Ma for most of the Wasatch Front. Age ranges within segments, arranged north to south, are as follows. Two samples from the Brigham City segment yield average sample ages of 4.5+/-1.3 to 5.7+/-1.2 Ma. Four samples from the Weber segment have ages of 3.8+/-0.3 to 6.4+/-1.7 Ma, with the youngest ages in the center of the segment. Two samples from the northern Salt Lake segment yield ages of 3.4+/-1.1 to 5.2+/-1.2 Ma. Two closely spaced samples from the Provo segment and one from the Nephi segment yield ages of 6.4+/-1.2 Ma. Typical age variations within and between segments are relatively small with overlapping uncertainties, except on the Salt Lake segment, where several multiple-grain furnace (U-Th)/He ages from the Cottonwood Intrusive Belt (CIB) in the southern Salt Lake segment (Armstrong et. al. AGU, 1999) are about half those of the rest of the segment and the Wasatch Front average. The relatively consistent late Miocene to early Pliocene ages along nearly 200 km of the WFZ suggest similar exhumation rates along most of the Wasatch front for the last ~6 Ma. With the exception of the CIB, simple calculations assuming monotonic cooling and typical geothermal

  20. Faulting pattern along slow-spreading ridge segments: a consequence of along-axis variation in lithospheric rheology

    NASA Astrophysics Data System (ADS)

    Thibaud, Rémy; Dauteuil, Olivier; Gente, Pascal

    1999-11-01

    We present here results from an analogue model designed to test the relative influence of along-axis variations of the crustal thickness and of the thermal structure of the lithosphere on the geometry and on the faulting pattern of the axial rift of a slow-spreading ridge. Rheologically calculated layered models are employed, using quartz sand and silicone putty as analogues of the brittle and ductile components of the lithosphere, respectively. Two parameters have been analysed in detail: (1) the thickness of the brittle layer, and (2) the viscosity of the ductile layer. This study shows that the thickening of the brittle layer and the increase of the viscosity of the ductile layer bring about a widening of the axial valley associated with an increase of the number of faults. A decrease of the depth of the axial valley and of the vertical throw of the faults is observed with an increase of the viscosity of the ductile layer and a decrease of the thickness of the brittle layer. These results are consistent with observations along Mid-Atlantic Ridge segments. For segment ends, the fault pattern obtained in the models is similar to that described on both sides of the axis for segments bordered by a zero-offset discontinuity, and on outside corners for segments bordered by a lateral offset discontinuity. Our results suggest that the viscosity of the ductile layer plays a more important role in the fault pattern than the thickness of the brittle layer. The influence of segment length, offset length and temporal variation in thermal input could explain the more or less important along-axis variation in the deformation pattern observed along segments of slow-spreading ridges.

  1. Style of the surface deformation by the 1999 Chichi earthquake at the central segment of Chelungpu fault, Taiwan, with special reference to the presence of the main and subsidiary faults and their progressive deformation in the Tsauton area

    NASA Astrophysics Data System (ADS)

    Ota, Y.; Watanabe, M.; Suzuki, Y.; Yanagida, M.; Miyawaki, A.; Sawa, H.

    2007-11-01

    We describe the style of surface deformation in the 1999 Chichi earthquake in the central segment of the Chelungpu Fault. The study covers the Kung-fu village, north of Han River, to the south of Tsauton area. A characteristic style of the surface deformation is a convex scarp in profile and sinuous plan view, due to the low angle thrust fault. Two subparallel faults, including the west facing Tsauton West fault, and the east facing Tsauton East fault, limit the western and eastern margin of the Tsauton terraced area. The Tsauton West fault is the continuation of the main Chelungpu fault and the Tsauton East fault is located about 2 km apart. Both faults record larger amounts of vertical displacement on the older terraces. The 1999 surface rupture occurred exactly on a pre-existing fault scarp of the Tsauton West and East faults. Thus, repeated activities of these two faults during the Holocene, possibly since the late Quaternary, are confirmed. The amount of vertical offset of the Tsauton East fault is smaller, and about 40-50% of that of the Tsauton West fault for the pre-existing fault. This indicates that the Tsauton East fault is a subsidiary fault and moved together with the main fault, but accommodated less amount.

  2. GPS measurements along the North Anatolian fault zone ont he Mid-Anatolia segment

    NASA Astrophysics Data System (ADS)

    Yavasoglu, H.; Team

    2003-04-01

    features of the NAF is seen in the central part. Here NAF consists of southward spliting concave branches. These splines have generally right-lateral slip compared these splays with the Riedel fractures. One of the biggest splays is known as Sungurlu fault. The other important splays are Merzifon and Lacin faults. Recent palaeomagnetic data indicated that the main Anatolian Block to the south of the Sungurlu fault rotated anticlockwise and the other blocks rotated clockwise and anticlockwise according to the orientation and the geometry of the faults bounding the blocks. In contrast to the other parts of the NAF, central part has not been studied in detail yet. The data, which will be produced in this project, are expected to add an important contribution to the present knowledge on the NAF. 3. THE GPS MEASUREMENTS 3.1 The Design of The Mid-NAF GPS Network The estimated lateral movement on the LVKI segment of NAF is approximately 2-3cm per year. In order to determine approximately 2-3 centimeters of movements, point marks in the network should be built with forced centering instruments (pillars or steel rods etc.). At first a study in advance is carried out in the study area to find out convenient old pillars. At the end of the study, useful already established 25 pillar points are determined on the region. However, it is decided that the network can consist of 16 station points, because of the reasons such as financial limitations and the number of GPS receivers. The network consists of 16 point. The points are given name with the four letter abbreviations of the nearest settlement. The GPS sites mainly were chosen as representative of the fault-bounded continental blocks. Although there are lots of faults in the area, active and recently earthquake produced faults and continental blocks that are bounded by these faults were taken into consideration. 3.2 GPS Measurements The number and features of receivers are Measurements were performed in six days at two stages. For

  3. Decisive factor in increase of loading at adjacent segments after lumbar fusion: operative technique, pedicle screws, or fusion itself: biomechanical analysis using finite element

    NASA Astrophysics Data System (ADS)

    Park, Joon-Hee; Kim, Ho-Joong; Kang, Kyoung-Tak; Kim, Ka-yeon; Chun, Heoung-Jae; Moon, Seong-Hwan; Lee, Hwan-Mo

    2010-03-01

    The aim of this study is to investigate the change in biomechanical milieu following removal of pedicle screws or removal of spinous process with posterior ligament complex in instrumented single level lumbar arthrodesis. We developed and validated a finite element model (FEM) of the intact lumbar spine (L2-4). Four scenarios of L3-4 lumbar fusion were simulated: posterolateral fusion (PLF) at L3-4 using pedicle screw system with preservation of PLC (Pp WiP), L3-4 lumbar posterolateral fusion state after removal of pedicle screw system with preservation of PLC (Pp WoP), L3-4 using pedicle screw system without preservation PLC (Sp WiP), L3-4 lumbar posterolateral fusion state after removal of pedicle screw system without preservation of PLC (Sp WoP). For these models, we investigated the range of motion and maximal Von mises stress of disc in all segments under various moments. All fusion models demonstrated increase in range of motion at adjacent segments compared to the intact model.For the four fusion models, the WiP model s P had the largest increase in range of motion at each adjacent segment. This study demonstrated that removal of pedicle screw system and preservation of PLC after complete lumbar spinal fusion could reduce the stress of adjacent segments synergistically and might have beneficial effects in preventing ASD.

  4. Decisive factor in increase of loading at adjacent segments after lumbar fusion: operative technique, pedicle screws, or fusion itself: biomechanical analysis using finite element

    NASA Astrophysics Data System (ADS)

    Park, Joon-Hee; Kim, Ho-Joong; Kang, Kyoung-Tak; Kim, Ka-Yeon; Chun, Heoung-Jae; Moon, Seong-Hwan; Lee, Hwan-Mo

    2009-12-01

    The aim of this study is to investigate the change in biomechanical milieu following removal of pedicle screws or removal of spinous process with posterior ligament complex in instrumented single level lumbar arthrodesis. We developed and validated a finite element model (FEM) of the intact lumbar spine (L2-4). Four scenarios of L3-4 lumbar fusion were simulated: posterolateral fusion (PLF) at L3-4 using pedicle screw system with preservation of PLC (Pp WiP), L3-4 lumbar posterolateral fusion state after removal of pedicle screw system with preservation of PLC (Pp WoP), L3-4 using pedicle screw system without preservation PLC (Sp WiP), L3-4 lumbar posterolateral fusion state after removal of pedicle screw system without preservation of PLC (Sp WoP). For these models, we investigated the range of motion and maximal Von mises stress of disc in all segments under various moments. All fusion models demonstrated increase in range of motion at adjacent segments compared to the intact model.For the four fusion models, the WiP model s P had the largest increase in range of motion at each adjacent segment. This study demonstrated that removal of pedicle screw system and preservation of PLC after complete lumbar spinal fusion could reduce the stress of adjacent segments synergistically and might have beneficial effects in preventing ASD.

  5. Geodetic Investigation of Compliant Fault Zones on the San Francisco Peninsula segment of the San Andreas Fault

    NASA Astrophysics Data System (ADS)

    Materna, K.; Burgmann, R.

    2015-12-01

    At many places along the San Andreas Fault, geodetic and seismic studies have suggested the presence of near-field compliant fault zones (CFZs). These zones of damaged rock display reduced elastic moduli compared to intact rock, resulting in both higher geodetic strain rates and lower seismic velocities within the fault zones. In this study, we investigate the CFZ surrounding the San Andreas Fault in the San Francisco Peninsula by examining interseismic deformation over the past several decades. We use new and existing survey GPS measurements, as well as older electronic distance measurements, to characterize the deformation of the CFZ. The data come from networks at Black Mountain and Lake San Andreas, both small-aperture geodetic networks on the San Francisco Peninsula with survey GPS occupations spanning at least 15 years. We compare the inferred fault zone properties between the two networks, which are separated by less than 40 kilometers but which represent different geologic boundaries and show different fault ages. We also compare patterns in seismicity between the two regions. The differences in inferred fault parameters between these two regions may be related to differences in fault age and development, giving clues into how CFZs develop over time.

  6. Radiologic Findings and Risk Factors of Adjacent Segment Degeneration after Anterior Cervical Discectomy and Fusion : A Retrospective Matched Cohort Study with 3-Year Follow-Up Using MRI

    PubMed Central

    So, Wan-Soo; Ku, Min-Geun; Kim, Sang-Hyeon; Kim, Dong-Won; Lee, Byung-Hun

    2016-01-01

    Objective The purpose of this study was to figure out the radiologic findings and risk factors related to adjacent segment degeneration (ASD) after anterior cervical discectomy and fusion (ACDF) using 3-year follow-up radiography, computed tomography (CT), and magnetic resonance image (MRI). Methods A retrospective matched comparative study was performed for 64 patients who underwent single-level ACDF with a cage and plate. Radiologic parameters, including upper segment range of motion (USROM), lower segment range of motion (LSROM), upper segment disc height (UDH), and lower segment disc height (LDH), clinical outcomes assessed with neck and arm visual analogue scale (VAS), and risk factors were analyzed. Results Patients were categorized into the ASD (32 patients) and non-ASD (32 patients) group. The decrease of UDH was significantly greater in the ASD group at each follow-up visit. At 36 months postoperatively, the difference for USROM value from the preoperative one significantly increased in the ASD group than non-ASD group. Preoperative other segment degeneration was significantly associated with the increased incidence of ASD at 36 months. However, pain intensity for the neck and arm was not significantly different between groups at any post-operative follow-up visit. Conclusion The main factor affecting ASD is preoperative other segment degeneration out of the adjacent segment. In addition, patients over the age of 50 are at higher risk of developing ASD. Although there was definite radiologic degeneration in the ASD group, no significant difference was observed between the ASD and non-ASD groups in terms of the incidence of symptomatic disease. PMID:26962418

  7. Growth and linkage of the quaternary Ubrique Normal Fault Zone, Western Gibraltar Arc: role on the along-strike relief segmentation

    NASA Astrophysics Data System (ADS)

    Jiménez-Bonilla, Alejandro; Balanya, Juan Carlos; Exposito, Inmaculada; Diaz-Azpiroz, Manuel; Barcos, Leticia

    2015-04-01

    Strain partitioning modes within migrating orogenic arcs may result in arc-parallel stretching that produces along-strike structural and topographic discontinuities. In the Western Gibraltar Arc, arc-parallel stretching has operated from the Lower Miocene up to recent times. In this study, we have reviewed the Colmenar Fault, located at the SW end of the Subbetic ranges, previously interpreted as a Middle Miocene low-angle normal fault. Our results allow to identify younger normal fault segments, to analyse their kinematics, growth and segment linkage, and to discuss its role on the structural and relief drop at regional scale. The Colmenar Fault is folded by post-Serravallian NE-SW buckle folds. Both the SW-dipping fault surfaces and the SW-plunging fold axes contribute to the structural relief drop toward the SW. Nevertheless, at the NW tip of the Colmenar Fault, we have identified unfolded normal faults cutting quaternary soils. They are grouped into a N110˚E striking brittle deformation band 15km long and until 3km wide (hereafter Ubrique Normal Fault Zone; UNFZ). The UNFZ is divided into three sectors: (a) The western tip zone is formed by normal faults which usually dip to the SW and whose slip directions vary between N205˚E and N225˚E. These segments are linked to each other by left-lateral oblique faults interpreted as transfer faults. (b) The central part of the UNFZ is composed of a single N115˚E striking fault segment 2,4km long. Slip directions are around N190˚E and the estimated throw is 1,25km. The fault scarp is well-conserved reaching up to 400m in its central part and diminishing to 200m at both segment terminations. This fault segment is linked to the western tip by an overlap zone characterized by tilted blocks limited by high-angle NNE-SSW and WNW-ESE striking faults interpreted as "box faults" [1]. (c) The eastern tip zone is formed by fault segments with oblique slip which also contribute to the downthrown of the SW block. This kinematic

  8. Controls on damage zone asymmetry of a normal fault zone: outcrop analyses of a segment of the Moab fault, SE Utah

    NASA Astrophysics Data System (ADS)

    Berg, Silje S.; Skar, Tore

    2005-10-01

    Outcrop data has been used to examine the spatial arrangement of fractures in the damage zones of a segment of the large-scale Moab Fault (45 km in length), SE Utah. The characteristics of the footwall and hanging wall damage zones show pronounced differences in the deformation pattern: (1) there is a well-developed syncline in the hanging wall, as opposed to sub-horizontal bedding of the footwall; (2) the footwall damage zone is sub-divided into an inner zone (0-5 m from fault core) and an outer zone (>5 m) based on differences in deformation band frequency, whereas no clear sub-division can be made in the hanging wall; (3) the hanging wall damage zone is more than three times wider than the footwall damage zone; (4) there is a higher abundance of antithetic fractures and deformation bands in the hanging wall than in the footwall; and (5) the antithetic structures generally have more gentle dips in the hanging wall than in the footwall. The main conclusion is that the structural pattern across the fault zone is strongly asymmetric. The deformation pattern is partly influenced by lithology and/or partly by processes associated with the development of the fault core. We suggest, however, that the most important cause for the asymmetric strain distribution is the development of the hanging wall syncline and the resulting asymmetric stress pattern expected to exist during fault propagation.

  9. Millennium recurrence interval of morphogenic earthquakes on the Qingchuan fault, northeastern segment of the Longmen Shan Thrust Belt, China

    NASA Astrophysics Data System (ADS)

    Lin, Aiming; Yan, Bing; Rao, Gang

    2016-04-01

    The 2008 M w 7.9 Wenchuan produced a ˜285-300-km-long coseismic surface rupture zone, including a 60-km-long segment along the Qingchuan fault, the northeastern segment of the Longmen Shan Thrust Belt (LSTB), Sichuan Basin, central China. Field investigations, trench excavations, and radiocarbon dating results reveal that (i) the Qingchuan fault is currently active as a seismogenic fault, along which four morphogenic earthquakes including the 2008 Wenchuan earthquake occurred in the past ca. 3500 years, suggesting an average millennium recurrence interval of morphogenic earthquakes in the late Holocene; (ii) the most recent event prior to the 2008 Wenchuan earthquake took place in the period between AD 1400 and AD 1100; (iii) the penultimate paleoseismic event occurred in the period around 2000 years BP in the Han Dynasty (206 BC-AD 220); (iv) the third paleoseismic event occurred in the period between 900 and 1800 BC; and (v) at least three seismic faulting events occurred in the early Holocene. The present results are comparable with those inferred in the central and southwestern segments of the LSTB within which the Wenchuan magnitude earthquakes occurred in a millennium recurrence interval, that are in contrast with previous estimates of 2000-10,000 years for the recurrence interval of morphogenic earthquakes within the LSTB and thereby necessitating substantial modifications to existing seismic hazard models for the densely populated region at the Sichuan region.

  10. Active fault segments as potential earthquake sources: Inferences from integrated geophysical mapping of the Magadi fault system, southern Kenya Rift

    NASA Astrophysics Data System (ADS)

    Kuria, Z. N.; Woldai, T.; van der Meer, F. D.; Barongo, J. O.

    2010-06-01

    Southern Kenya Rift has been known as a region of high geodynamic activity expressed by recent volcanism, geothermal activity and high rate of seismicity. The active faults that host these activities have not been investigated to determine their subsurface geometry, faulting intensity and constituents (fluids, sediments) for proper characterization of tectonic rift extension. Two different models of extension direction (E-W to ESE-WNW and NW-SE) have been proposed. However, they were based on limited field data and lacked subsurface investigations. In this research, we delineated active fault zones from ASTER image draped on ASTER DEM, together with relocated earthquakes. Subsequently, we combined field geologic mapping, electrical resistivity, ground magnetic traverses and aeromagnetic data to investigate the subsurface character of the active faults. Our results from structural studies identified four fault sets of different age and deformational styles, namely: normal N-S; dextral NW-SE; strike slip ENE-WSW; and sinistral NE-SW. The previous studies did not recognize the existence of the sinistral oblique slip NE-SW trending faults which were created under an E-W extension to counterbalance the NW-SE faults. The E-W extension has also been confirmed from focal mechanism solutions of the swarm earthquakes, which are located where all the four fault sets intersect. Our findings therefore, bridge the existing gap in opinion on neo-tectonic extension of the rift suggested by the earlier authors. Our results from resistivity survey show that the southern faults are in filled with fluid (0.05 and 0.2 Ωm), whereas fault zones to the north contain high resistivity (55-75 Ωm) material. The ground magnetic survey results have revealed faulting activity within active fault zones that do not contain fluids. In addition, the 2D inversion of the four aero-magnetic profiles (209 km long) revealed: major vertical to sub vertical faults (dipping 75-85° east or west); an

  11. Tilted lake shorelines record the onset of motion along the Hilton Creek fault adjacent to Long Valley caldera, CA, USA

    NASA Astrophysics Data System (ADS)

    Perkins, J. P.; Finnegan, N. J.; Cervelli, P. F.; Langbein, J. O.

    2010-12-01

    Prominent normal faults occur within and around Long Valley caldera, in the eastern Sierra Nevada of California. However, their relationship to both the magmatic and tectonic evolution of the caldera since the 760 ka eruption of the Bishop Tuff remains poorly understood. In particular, in the Mono-Inyo Craters north of Long Valley, extensional faulting appears to be replaced by dike intrusion where magma is available in the crust. However, it is unclear whether extensional faults in Long Valley caldera have been active since the eruption of the Bishop Tuff (when the current topography was established) or are a relatively young phenomenon owing to the cooling and crystallization of the Long Valley magma reservoir. Here we use GPS geodesy and geomorphology to investigate the evolution of the Hilton Creek fault, the primary range-front fault bounding Long Valley caldera to the southwest. Our primary goals are to determine how long the Hilton Creek fault has been active and whether slip rates have been constant over that time interval. To characterize the modern deformation field, we capitalize on recently (July, 2010) reoccupied GPS benchmarks first established in 1999-2000. These fixed-array GPS data show no discernible evidence for recent slip on the Hilton Creek fault, which further highlights the need for longer-term constraints on fault motion. To establish a fault slip history, we rely on a suite of five prominent shorelines from Pleistocene Long Valley Lake whose ages are well constrained based on field relationships to dated lavas, and that are tilted southward toward the Hilton Creek fault. A preliminary analysis of shoreline orientations using GPS surveys and a 5-m-resolution Topographic Synthetic Aperture Radar (TOPSAR) digital elevation model shows that lake shorelines tilt towards the Hilton Creek fault at roughly parallel gradients (~ 0.6%). The measured shorelines range in inferred age from 100 ka to 500 ka, which constrain recent slip on the Hilton

  12. Pliocene transpressional modification of depositional basins by convergent thrusting adjacent to the "Big Bend" of the San Andreas fault: An example from Lockwood Valley, southern California

    USGS Publications Warehouse

    Kellogg, K.S.; Minor, S.A.

    2005-01-01

    The "Big Bend" of the San Andreas fault in the western Transverse Ranges of southern California is a left stepping flexure in the dextral fault system and has long been recognized as a zone of relatively high transpression compared to adjacent regions. The Lockwood Valley region, just south of the Big Bend, underwent a profound change in early Pliocene time (???5 Ma) from basin deposition to contraction, accompanied by widespread folding and thrusting. This change followed the recently determined initiation of opening of the northern Gulf of California and movement along the southern San Andreas fault at about 6.1 Ma, with the concomitant formation of the Big Bend. Lockwood Valley occupies a 6-km-wide, fault-bounded structural basin in which converging blocks of Paleoproterozoic and Cretaceous crystalline basement and upper Oligocene and lower Miocene sedimentary rocks (Plush Ranch Formation) were thrust over Miocene and Pliocene basin-fill sedimentary rocks (in ascending order, Caliente Formation, Lockwood Clay, and Quatal Formation). All the pre-Quatal sedimentary rocks and most of the Pliocene Quatal Formation were deposited during a mid-Tertiary period of regional transtension in a crustal block that underwent little clockwise vertical-axis rotation as compared to crustal blocks to the south. Ensuing Pliocene and Quaternary transpression in the Big Bend region began during deposition of the poorly dated Quatal Formation and was marked by four converging thrust systems, which decreased the areal extent of the sedimentary basin and formed the present Lockwood Valley structural basin. None of the thrusts appears presently active. Estimated shortening across the center of the basin was about 30 percent. The fortnerly defined eastern Big Pine fault, now interpreted to be two separate, oppositely directed, contractional reverse or thrust faults, marks the northwestern structural boundary of Lockwood Valley. The complex geometry of the Lockwood Valley basin is similar

  13. Characterizing the Variability of Supercycles on the Mentawai Segment of the Sunda Megathrust and Implications for Global Fault Behavior

    NASA Astrophysics Data System (ADS)

    Philibosian, B.; Sieh, K.; Avouac, J. P.; Natawidjaja, D. H.; Chiang, H. W.; WU, C. C.; Perfettini, H.; Shen, C. C.; Daryono, M. R.; Suwargadi, B. W.

    2014-12-01

    One of the key lessons of the last decade of great earthquakes is that long paleoseismic records are a vital part of the body of knowledge required for accurate earthquake forecasting, and that the longest, most detailed records provide the best understanding of the complete range of fault behavior. In addition to being the source of one of the decade's great earthquakes, the Mentawai segment of the Sunda megathrust also has one of the most detailed paleoseismic and paleogeodetic records, thanks to studies of coral microatolls. The high spatial and temporal resolution of these records has illuminated many features that are difficult to discern using most other techniques. Examples of varying types of segmentation, asperity mosaicking, superimposed seismic cycles with varying periods, and time-varying interseismic coupling are all exhibited by this megathrust segment. While the northern end of the segment in the Batu Islands appears to be a persistent barrier to rupture throughout the paleoseismic record, the behavior of the central Mentawai segment is more heterogeneous. Ruptures from both ends generally terminate in this region, yet also often overlap by 100-200 km. This behavior, likely due to smaller-scale heterogeneities in frictional properties of the fault interface, results in the characteristic rupture of the Mentawai segment in a series of events rather than a single end-to-end rupture. Beyond that similarity, it is clear that each of these rupture sequences evolves uniquely in terms of the order and grouping of asperities that rupture. Additionally, the ruptures that begin the sequences frequently alter the distribution of fault coupling, thus influencing the progression of future ruptures. Heterogeneities in fault frictional properties at the scale seen in the Mentawai case are probably common and control the rupture extent, magnitude and distribution of slip in great earthquakes worldwide. Though the details are usually less clear, analogs to the

  14. Segment-scale and intrasegment lithospheric thickness and melt variations near the Andrew Bain megatransform fault and Marion hot spot: Southwest Indian Ridge, 25.5°E-35°E

    NASA Astrophysics Data System (ADS)

    Takeuchi, Christopher S.; Sclater, John G.; Grindlay, Nancy R.; Madsen, John A.; Rommevaux-Jestin, CéLine

    2010-07-01

    We analyze bathymetric, gravimetric, and magnetic data collected on cruise KN145L16 between 25.5°E and 35°E on the ultraslow spreading Southwest Indian Ridge, where the 750 km long Andrew Bain transform domain separates two accretionary segments to the northeast from a single segment to the southwest. Similar along-axis asymmetries in seafloor texture, rift valley curvature, magnetic anomaly amplitude, magnetization intensity, and mantle Bouguer anomaly (MBA) amplitude within all three segments suggest that a single mechanism may produce variable intrasegment lithospheric thickness and melt delivery. However, closer analysis reveals that a single mechanism is unlikely. In the northeast, MBA lows, shallow axial depths, and large abyssal hills indicate that the Marion hot spot enhances the melt supply to the segments. We argue that along-axis asthenospheric flow from the hot spot, dammed by major transform faults, produces the inferred asymmetries in lithospheric thickness and melt delivery. In the southwest, strong rift valley curvature and nonvolcanic seafloor near the Andrew Bain transform fault indicate very thick subaxial lithosphere at the end of the single segment. We suggest that cold lithosphere adjacent to the eastern end of the ridge axis cools and thickens the subaxial lithosphere, suppresses melt production, and focuses melt to the west. This limits the amount of melt emplaced at shallow levels near the transform fault. Our analysis suggests that the Andrew Bain divides a high melt supply region to the northeast from an intermediate to low melt supply region to the southwest. Thus, this transform fault represents not only a major topographic feature but also a major melt supply boundary on the Southwest Indian Ridge.

  15. Millennium recurrence interval of morphogenic earthquakes on the Qingchuan fault, northeastern segment of the Longmen Shan Thrust Belt, China

    NASA Astrophysics Data System (ADS)

    Lin, A.

    2015-12-01

    In this study, I present new paleoseismic and topographic evidence for the Holocene faulting activity, including the recurrence interval of morphogenic earthquakes and the slip rate along the Qingchuan fault, the northern segment of the Longmen Shan Thrust Belt, central China, and discuss its tectonic implications for the zone at the eastern margin of the Tibetan Plateau. Field investigations, trench excavations, and radiocarbon dating results reveal that: (i) the Qingchuan fault is currently active as a seismogenic fault, along which six morphogenic earthquakes occurred in the past 6000 years; (ii) the most recent event prior to the 2008 Wenchuan earthquake took place in the period between AD 600 and 1400, which probably corresponds to the late Tang-Song (AD 800-1000) (M~8) earthquake that occurred in the central and southwestern segments of the LSTB; (iii) the penultimate paleoseismic event occurred in the period around 2000 yr BP, suggesting a millennium recurrence interval of morphogenic earthquakes in the late Holocene. The present results are comparable with those inferred in the central and southwestern segments of the LSTB within which the Wenchuan-magnitude earthquakes occurred in a millennium recurrence interval, that are in contrast with previous estimates of 2000-10,000 years for the recurrence interval of morphogenic earthquakes within the LSTB, and thereby necessitating substantial modifications to exiting seismic-hazard models for the densely populated region at the Sichuan region. References: 1) Lin, A., Rao, G., and Yan, B., 2012. Field evidence of rupture of the Qingchuan Fault during the 2008 Mw7.9 Wenchuan earthquake, northeastern segment of the Longmen Shan Thrust Belt, China. Tectonophysics, 522-523, 243-252, doi:10.1016/j.tecto.2011.12.012 2) Lin, A., Rao, G., and Yan, B., 2014. Structural analysis of the right-lateral strike-slip Qingchuan fault, northeastern segment of the Longmen Shan thrust belt, central China. Journal of Structural

  16. Segmented Coil Fails In Steps

    NASA Technical Reports Server (NTRS)

    Stedman, Ronald S.

    1990-01-01

    Electromagnetic coil degrades in steps when faults occur, continues to operate at reduced level instead of failing catastrophically. Made in segments connected in series and separated by electrically insulating barriers. Fault does not damage adjacent components or create hazard. Used to control valves in such critical applications as cooling systems of power generators and chemical process equipment, where flammable liquids or gases handled. Also adapts to electrical control of motors.

  17. Investigating fault propagation and segment linkage using throw distribution analysis within the Agbada formation of Ewan and Oloye fields, northwestern Niger delta

    NASA Astrophysics Data System (ADS)

    Durogbitan, Abimbola Adewole

    2016-08-01

    Throw distribution analysis of the key stratigraphic surfaces (sequence boundaries and maximum flooding surfaces) across faults has allowed detailed investigation of the tectonic history within the Ewan and Oloye fields, northwestern Niger delta. The structure in the studied area is dominated by growth fault systems which are listric in cross section and concave to the basin in plan-view. Generally, the faults are active down to 2000 m depth before they die out or sole into the underlying shale. The hanging-wall blocks of growth faults are deformed into broad rollover anticlines, with some synthetic and antithetic faults initiated from the anticline crests, and fault splays off major faults, further complicating these structures. Stratigraphic key surfaces within the syn-faulting succession range in age from 16.7 to 10.35 Ma. Periods of maximum and minimum throw are established from 2-Dimensional throw distribution on the growth fault plane. Throw distribution allows analysis of growth fault nucleation, propagation and linkage. Each fault nucleated at different and a distinct interval within the stratigraphic section, as a result of the paleo-stress distribution between the interacting faults. Nucleation and linkage positions can be identified at points of maximum and minimum throw respectively. Following nucleation, faults propagated radially and linked to form the present geometry. Within the study area, fault propagation and segment linkage (lateral and vertical) are important features of the fault system. Understanding of growth fault evolution and linkage has greatly improved prediction of seal potential, trap geometry and migration. The accurate timing of the segment linkage has helped to evaluate the seal risk.

  18. Investigating fault propagation and segment linkage using throw distribution analysis within the Agbada formation of Ewan and Oloye fields, northwestern Niger delta

    NASA Astrophysics Data System (ADS)

    Durogbitan, Abimbola Adewole

    2016-08-01

    Throw distribution analysis of the key stratigraphic surfaces (sequence boundaries and maximum flooding surfaces) across faults has allowed detailed investigation of the tectonic history within the Ewan and Oloye fields, northwestern Niger delta. The structure in the studied area is dominated by growth fault systems which are listric in cross section and concave to the basin in plan-view. Generally, the faults are active down to 2000 m depth before they die out or sole into the underlying shale. The hanging-wall blocks of growth faults are deformed into broad rollover anticlines, with some synthetic and antithetic faults initiated from the anticline crests, and fault splays off major faults, further complicating these structures. Stratigraphic key surfaces within the syn-faulting succession range in age from 16.7 to 10.35 Ma. Periods of maximum and minimum throw are established from 2-Dimensional throw distribution on the growth fault plane. Throw distribution allows analysis of growth fault nucleation, propagation and linkage. Each fault nucleated at different and a distinct interval within the stratigraphic section, as a result of the paleo-stress distribution between the interacting faults. Nucleation and linkage positions can be identified at points of maximum and minimum throw respectively. Following nucleation, faults propagated radially and linked to form the present geometry. Within the study area, fault propagation and segment linkage (lateral and vertical) are important features of the fault system. Understanding of growth fault evolution and linkage has greatly improved prediction of seal potential, trap geometry and migration. The accurate timing of the segment linkage has helped to evaluate the seal risk.

  19. Stress evolution and seismic hazard on the Maqin-Maqu segment of East Kunlun Fault zone from co-, post- and interseismic stress changes

    NASA Astrophysics Data System (ADS)

    Shan, Bin; Xiong, Xiong; Wang, Rongjiang; Zheng, Yong; Yadav, R. B. S.

    2015-01-01

    The East Kunlun Fault zone, striking E-W to WNW-ESE, has been recognized as one of the largest and most active left-lateral strike-slip faults in the China continent. Presently, the Maqin-Maqu segment (MMS) is recognized as a seismic gap on the East Kunlun Fault. Since several highly populated counties are close to this region, understanding stress transfer and accumulation along this segment is important for hazard assessment along the MMS. In this study, we calculated the stress evolution along the MMS of the East Kunlun Fault zone during 1879-2008 by integrating coseismic effects, viscoelastic relaxation and tectonic loading. It is observed that the stress accumulation on the western part of the Maqin segment has been effected by the 1937 Tuosuo Lake earthquake, the stress on the eastern part of the Maqin segment. Also, the western part of the Maqu segment was relaxed by the 1947 Dari earthquake, and the stress loading on the eastern part of Maqu segment was increased by both the 1879 Wudu and 2008 Wenchuan earthquakes. It is observed that, compared to coseismic static stress changes, the post-seismic viscoelastic relaxation process has played a more important role on stress accumulation in the Maqu segment. The increased stress on the Maqin and Maqu segment is consistent with tectonic loading over 160 and 250 yr, respectively, which we expect will lead to future earthquakes and associated seismic hazard on these segments.

  20. 40Ar/ 39Ar dating constraints on the high-angle normal faulting along the southern segment of the Tan-Lu fault system: An implication for the onset of eastern China rift-systems

    NASA Astrophysics Data System (ADS)

    Wang, Yu; Zhou, Su

    2009-01-01

    High-angle normal faulting in eastern China was an important tectonic process responsible for the rifting of the eastern Asian continental margin. Along the southern segment of the Tan-Lu fault system, part of the eastern China rift-system, 55-70° east-dipping normal faults are the oldest structures within this rift-system. Chlorite, pseudotachylite, and fault breccia are found in fault zones, which are characterized by microstructures and syn-deformation chlorite minerals aligned parallel to a down-dip stretching lineation. 40Ar/ 39Ar dating of syn-deformation chlorite and K-feldspar from the fault gouge zone yields cooling ages of ˜75-70 Ma, interpreted as the timing of slip along the normal faults. This age is older than that of opening of the Japanese sea and back-arc extension in the west Pacific, but similar to the onset of the Indo-Asian (soft?) collision.

  1. Changes in the Expressions of Iba1 and Calcitonin Gene-Related Peptide in Adjacent Lumbar Spinal Segments after Lumbar Disc Herniation in a Rat Model

    PubMed Central

    2015-01-01

    Lumbar disc herniation is commonly encountered in clinical practice and can induce sciatica due to mechanical and/or chemical irritation and the release of proinflammatory cytokines. However, symptoms are not confined to the affected spinal cord segment. The purpose of this study was to determine whether multisegmental molecular changes exist between adjacent lumbar spinal segments using a rat model of lumbar disc herniation. Twenty-nine male Sprague-Dawley rats were randomly assigned to either a sham-operated group (n=10) or a nucleus pulposus (NP)-exposed group (n=19). Rats in the NP-exposed group were further subdivided into a significant pain subgroup (n=12) and a no significant pain subgroup (n=7) using mechanical pain thresholds determined von Frey filaments. Immunohistochemical stainings of microglia (ionized calcium-binding adapter molecule 1; Iba1), astrocytes (glial fibrillary acidic protein; GFAP), calcitonin gene-related peptide (CGRP), and transient receptor potential vanilloid 1 (TRPV1) was performed in spinal dorsal horns and dorsal root ganglions (DRGs) at 10 days after surgery. It was found immunoreactivity for Iba1-positive microglia was higher in the L5 (P=0.004) dorsal horn and in the ipsilateral L4 (P=0.009), L6 (P=0.002), and S1 (P=0.002) dorsal horns in the NP-exposed group than in the sham-operated group. The expression of CGRP was also significantly higher in ipsilateral L3, L4, L6, and S1 segments and in L5 DRGs at 10 days after surgery in the NP-exposed group than in the sham-operated group (P<0.001). Our results indicate that lumbar disc herniation upregulates microglial activity and CGRP expression in many adjacent and ipsilateral lumbar spinal segments. PMID:26713069

  2. Near-surface structure of the 1906 main trace of the San Andreas Fault, San Francisco peninsula segment, California

    NASA Astrophysics Data System (ADS)

    Rosa, C.; Catchings, R. D.; Rymer, M. J.; Goldman, M.; Grove, K.; Prentice, C. S.

    2012-12-01

    The peninsula segment of the San Andreas Fault (SAF) is forecasted to have the second highest probability of producing a M6.7 or greater earthquake in the San Francisco Bay Area in the next 30 years; yet, relatively little is known about its slip history. In most places, the surface location of the SAF has been determined primarily on the basis of geomorphic features and from mapping surface ruptures associated with the 1906 M7.9 San Francisco earthquake. To more precisely locate traces of this segment of the SAF along the San Francisco peninsula in the subsurface, we acquired a high-resolution seismic imaging survey, using both seismic refraction and reflection profiling, south of Upper Crystal Springs Reservoir near Woodside, California in June 2012. High-resolution seismic images produced from this study may benefit ongoing paleoseismological investigations along the SAF because the seismic data can be used to precisely locate the main fault trace and auxiliary faults that may contribute to the earthquake hazards associated with the fault zone. Furthermore, the seismic images provide insights into near-surface fault structure and P- and S-wave velocities, which can be important in understanding strong shaking resulting from future earthquakes along this segment of the SAF. We acquired both P- and S-wave data using a 60-channel seismograph system connected via cable to 40-Hz vertical-component and 4-Hz horizontal geophones, which were spaced at 1-m intervals along a 60-m-long transect. Seismic sources (shots) were generated by hammer impacts on a steel plate or aluminum block at each geophone location. All shots were recorded on all channels. This survey design permits simultaneous acquisition of reflection and refraction data so that both refraction tomography and reflection images can be developed. Our initial analysis of the P-wave data shows that seismic velocities across the main trace of the SAF vary from about 700 m/s near the surface to more than 2500 m

  3. Oceanic transform earthquakes with unusual mechanisms or locations - Relation to fault geometry and state of stress in the adjacent lithosphere

    NASA Technical Reports Server (NTRS)

    Wolfe, Cecily J.; Bergman, Eric A.; Solomon, Sean C.

    1993-01-01

    Results are presented of a search for transform earthquakes departing from the pattern whereby they occur on the principal transform displacement zone (PTDZ) and have strike-slip mechanisms consistent with transform-parallel motion. The search was conducted on the basis of source mechanisms and locations taken from the Harvard centroid moment tensor catalog and the bulletin of the International Seismological Center. The source mechanisms and centroid depths of 10 such earthquakes on the St. Paul's, Marathon, Owen, Heezen, Tharp, Menard, and Rivera transforms are determined from inversions of long-period body waveforms. Much of the anomalous earthquake activity on oceanic transforms is associated with complexities in the geometry of the PTDZ or the presence of large structural features that may influence slip on the fault.

  4. Good Functional Outcome and Adjacent Segment Disc Quality 10 Years after Single-Level Anterior Lumbar Interbody Fusion with Posterior Fixation

    PubMed Central

    Horsting, Philip P.; Pavlov, Paul W.; Jacobs, Wilco C.H.; Obradov-Rajic, Marina; de Kleuver, Marinus

    2012-01-01

    We reviewed the records of a prospective consecutive cohort to evaluate the clinical performance of anterior lumbar interbody fusion with a titanium box cage and posterior fixation, with emphasis on long-term functional outcome. Thirty-two patients with chronic low back pain underwent anterior lumbar interbody fusion and posterior fixation. Radiological and functional results (visual analogue scale [VAS] and Oswestry score) were evaluated. Adjacent segment degeneration (ASD) was evaluated radiologically and by magnetic resonance imaging (MRI). Twenty-five patients (78%) were available for follow-up. Functional scores showed significant improvement in pain and function up to the 2-year follow-up observation. At 4 years, there was some deterioration of the clinical results. At 10-year follow-up, results remained stable compared with 4-year results. MRI showed ASD in 3/25 (12%) above and 2/10 (20%) below index level (compared with absent preoperatively). ASD could not be related to clinical outcome in this study. Anterior lumbar interbody fusion and posterior fixation is safe and effective. Initial improvement in VAS and Oswestry scores is partly lost at the 4-year follow-up. Good clinical results are maintained at 10-year follow-up and are not related to adjacent segment degeneration. PMID:24353942

  5. Effects of Fault Segmentation, Mechanical Interaction, and Structural Complexity on Earthquake-Generated Deformation

    NASA Astrophysics Data System (ADS)

    Haddad, David Elias

    Earth's topographic surface forms an interface across which the geodynamic and geomorphic engines interact. This interaction is best observed along crustal margins where topography is created by active faulting and sculpted by geomorphic processes. Crustal deformation manifests as earthquakes at centennial to millennial timescales. Given that nearly half of Earth's human population lives along active fault zones, a quantitative understanding of the mechanics of earthquakes and faulting is necessary to build accurate earthquake forecasts. My research relies on the quantitative documentation of the geomorphic expression of large earthquakes and the physical processes that control their spatiotemporal distributions. The first part of my research uses high-resolution topographic lidar data to quantitatively document the geomorphic expression of historic and prehistoric large earthquakes. Lidar data allow for enhanced visualization and reconstruction of structures and stratigraphy exposed by paleoseismic trenches. Lidar surveys of fault scarps formed by the 1992 Landers earthquake document the centimeter-scale erosional landforms developed by repeated winter storm-driven erosion. The second part of my research employs a quasi-static numerical earthquake simulator to explore the effects of fault roughness, friction, and structural complexities on earthquake-generated deformation. My experiments show that fault roughness plays a critical role in determining fault-to-fault rupture jumping probabilities. These results corroborate the accepted 3-5 km rupture jumping distance for smooth faults. However, my simulations show that the rupture jumping threshold distance is highly variable for rough faults due to heterogeneous elastic strain energies. Furthermore, fault roughness controls spatiotemporal variations in slip rates such that rough faults exhibit lower slip rates relative to their smooth counterparts. The central implication of these results lies in guiding the

  6. Near-Surface Structure of the Peninsula Segment of the San Andreas Fault, San Francisco Bay Area, California

    NASA Astrophysics Data System (ADS)

    Rosa, C.; Catchings, R.; Rymer, M. J.; Goldman, M.; Grove, K.; Prentice, C. S.

    2013-12-01

    The peninsula segment of the San Andreas Fault (SAF) is a section of the fault that has the potential to produce the next large earthquake in the San Francisco Bay Area, yet the slip history of the peninsula segment is relatively unknown. In most places, the surface location of the SAF has been determined primarily on the basis of geomorphic features and from mapping surface ruptures associated with the 1906 M7.9 San Francisco earthquake. To more precisely locate traces of the SAF along the San Francisco peninsula in the subsurface, we acquired a high-resolution seismic imaging survey, using both seismic refraction and reflection profiling, south of Upper Crystal Springs Reservoir near Woodside, California in June 2012. We acquired coincident P- and S-wave data using a 60-channel seismograph system connected via cable to 40-Hz vertical-component and 4-Hz horizontal-component geophones, with spacing at 1-m intervals along a 60-m-long transect across the SAF. Seismic sources (shots) were generated by hammer impacts on a steel plate or aluminum block at each geophone location. All shots were recorded on all channels. This survey design permitted simultaneous acquisition of reflection and refraction data such that both refraction tomography and reflection images were developed. Analysis of the P- and S-wave data, using refraction tomography, shows abrupt variations in the P-wave (Vp) and S-wave (Vs) velocities, including the 1,500 m/s velocity contour that outlines the top to groundwater and images of Vp/Vs and Poisson's ratios. P-wave velocities range from about 700 m/s at the surface to more than 4000 m/s at 20-m depth. S-wave velocities range from about 300 m/s at the surface to about 800 m/s at 20-m depth. The combined data indicate that the near-surface trace of the SAF dips steeply to the southwest in the upper few tens of meters. Variations in the velocity images also suggest the possibility of two additional near-surface fault traces within about 25 m of the

  7. Geometry, slip distribution, and kinematics of surface rupture on the Sakarya fault segment during the 17 August 1999 İzmit, Turkey, earthquake

    USGS Publications Warehouse

    Langridge, R.M.; Stenner, H.D.; Fumal, T.E.; Christofferson, S.A.; Rockwell, T.K.; Hartleb, R.D.; Bachhuber, J.; Barka, A.A.

    2002-01-01

    The Mw 7.4 17 August 1999 İzmit earthquake ruptured five major fault segments of the dextral North Anatolian Fault Zone. The 26-km-long, N86°W-trending Sakarya fault segment (SFS) extends from the Sapanca releasing step-over in the west to near the town of Akyazi in the east. The SFS emerges from Lake Sapanca as two distinct fault traces that rejoin to traverse the Adapazari Plain to Akyazi. Offsets were measured across 88 cultural and natural features that cross the fault, such as roads, cornfield rows, rows of trees, walls, rails, field margins, ditches, vehicle ruts, a dike, and ground cracks. The maximum displacement observed for the İzmit earthquake (∼5.1 m) was encountered on this segment. Dextral displacement for the SFS rises from less than 1 m at Lake Sapanca to greater than 5 m near Arifiye, only 3 km away. Average slip decreases uniformly to the east from Arifiye until the fault steps left from Sagir to Kazanci to the N75°W, 6-km-long Akyazi strand, where slip drops to less than 1 m. The Akyazi strand passes eastward into the Akyazi Bend, which consists of a high-angle bend (18°-29°) between the Sakarya and Karadere fault segments, a 6-km gap in surface rupture, and high aftershock energy release. Complex structural geometries exist between the İzmit, Düzce, and 1967 Mudurnu fault segments that have arrested surface ruptures on timescales ranging from 30 sec to 88 days to 32 yr. The largest of these step-overs may have acted as a rupture segmentation boundary in previous earthquake cycles.

  8. Fine structure of the landers fault zone: Segmentation and the rupture process

    USGS Publications Warehouse

    Li, Y.-G.; Vidale, J.E.; Aki, K.; Marone, C.J.; Lee, W.H.K.

    1994-01-01

    Observations and modeling of 3- to 6-hertz seismic shear waves trapped within the fault zone of the 1992 Landers earthquake series allow the fine structure and continuity of the zone to be evaluated. The fault, to a depth of at least 12 kilometers, is marked by a zone 100 to 200 meters wide where shear velocity is reduced by 30 to 50 percent. This zone forms a seismic waveguide that extends along the southern 30 kilometers of the Landers rupture surface and ends at the fault bend about 18 kilometers north of the main shock epicenter. Another fault plane waveguide, disconnected from the first, exists along the northern rupture surface. These observations, in conjunction with surface slip, detailed seismicity patterns, and the progression of rupture along the fault, suggest that several simple rupture planes were involved in the Landers earthquake and that the inferred rupture front hesitated or slowed at the location where the rupture jumped from one to the next plane. Reduction in rupture velocity can tentatively be attributed to fault plane complexity, and variations in moment release can be attributed to variations in available energy.

  9. Fine structure of the landers fault zone: segmentation and the rupture process.

    PubMed

    Li, Y G; Aki, K; Vidale, J E; Lee, W H; Marone, C J

    1994-07-15

    Observations and modeling of 3- to 6-hertz seismic shear waves trapped within the fault zone of the 1992 Landers earthquake series allow the fine structure and continuity of the zone to be evaluated. The fault, to a depth of at least 12 kilometers, is marked by a zone 100 to 200 meters wide where shear velocity is reduced by 30 to 50 percent. This zone forms a seismic waveguide that extends along the southern 30 kilometers of the Landers rupture surface and ends at the fault bend about 18 kilometers north of the main shock epicenter. Another fault plane waveguide, disconnected from the first, exists along the northern rupture surface. These observations, in conjunction with surface slip, detailed seismicity patterns, and the progression of rupture along the fault, suggest that several simple rupture planes were involved in the Landers earthquake and that the inferred rupture front hesitated or slowed at the location where the rupture jumped from one to the next plane. Reduction in rupture velocity can tentatively be attributed to fault plane complexity, and variations in moment release can be attributed to variations in available energy.

  10. Paleoseismic evidence of characteristic slip on the Western segment of the North Anatolian fault, Turkey

    USGS Publications Warehouse

    Klinger, Yann; Sieh, K.; Altunel, E.; Akoglu, A.; Barka, A.; Dawson, Tim; Gonzalez, Tania; Meltzner, A.; Rockwell, Thomas

    2003-01-01

    We have conducted a paleoseismic investigation of serial fault rupture at one site along the 110-km rupture of the North Anatolian fault that produced the Mw 7.4 earthquake of 17 August 1999. The benefit of using a recent rupture to compare serial ruptures lies in the fact that the location, magnitude, and slip vector of the most recent event are all very well documented. We wished to determine whether or not the previous few ruptures of the fault were similar to the recent one. We chose a site at a step-over between two major strike-slip traces, where the principal fault is a normal fault. Our two excavations across the 1999 rupture reveal fluvial sands and gravels with two colluvial wedges related to previous earthquakes. Each wedge is about 0.8 m thick. Considering the processes of collapse and subsequent diffusion that are responsible for the formation of a colluvial wedge, we suggest that the two paleoscarps were similar in height to the 1999 scarp. This similarity supports the concept of characteristic slip, at least for this location along the fault. Accelerator mass spectrometry (AMS) radiocarbon dates of 16 charcoal samples are consistent with the interpretation that these two paleoscarps formed during large historical events in 1509 and 1719. If this is correct, the most recent three ruptures at the site have occurred at 210- and 280-year intervals.

  11. Seismicity and Crustal Anisotropy Beneath the Western Segment of the North Anatolian Fault: Results from a Dense Seismic Array

    NASA Astrophysics Data System (ADS)

    Turkelli, N.; Teoman, U.; Altuncu Poyraz, S.; Cambaz, D.; Mutlu, A. K.; Kahraman, M.; Houseman, G. A.; Rost, S.; Thompson, D. A.; Cornwell, D. G.; Utkucu, M.; Gülen, L.

    2013-12-01

    The North Anatolian Fault (NAF) is one of the major strike slip fault systems on Earth comparable to San Andreas Fault in some ways. Devastating earthquakes have occurred along this system causing major damage and casualties. In order to comprehensively investigate the shallow and deep crustal structure beneath the western segment of NAF, a temporary dense seismic network for North Anatolia (DANA) consisting of 73 broadband sensors was deployed in early May 2012 surrounding a rectangular grid of by 70 km and a nominal station spacing of 7 km with the aim of further enhancing the detection capability of this dense seismic array. This joint project involves researchers from University of Leeds, UK, Bogazici University Kandilli Observatory and Earthquake Research Institute (KOERI), and University of Sakarya and primarily focuses on upper crustal studies such as earthquake locations (especially micro-seismic activity), receiver functions, moment tensor inversions, shear wave splitting, and ambient noise correlations. To begin with, we obtained the hypocenter locations of local earthquakes that occured within the DANA network. The dense 2-D grid geometry considerably enhanced the earthquake detection capability which allowed us to precisely locate events with local magnitudes (Ml) less than 1.0. Accurate earthquake locations will eventually lead to high resolution images of the upper crustal structure beneath the northern and southern branches of NAF in Sakarya region. In order to put additional constraints on the active tectonics of the western part of NAF, we also determined fault plane solutions using Regional Moment Tensor Inversion (RMT) and P wave first motion methods. For the analysis of high quality fault plane solutions, data from KOERI and the DANA project were merged. Furthermore, with the aim of providing insights on crustal anisotropy, shear wave splitting parameters such as lag time and fast polarization direction were obtained for local events recorded

  12. Kinematics of a Strike-Slip Fault Segment at Various Time Scales, Determined From GPS and Geomorphic Measurements: the Example of the Wadi Araba Fault, Dead Sea Transform.

    NASA Astrophysics Data System (ADS)

    Le Beon, M.; Klinger, Y.; Amrat, A.; Agnon, A.; Meriaux, A.; Dorbath, L.; Baer, G.; Finkel, R. C.; Ruegg, J.; Charade, O.; Elias, A.; Mayyas, O.; Ryerson, F. J.; Tapponnier, P.

    2008-12-01

    This work investigates slip rate evolution over time along one large strike-slip fault, the Dead Sea Transform (DST), which is the 1000-km long plate boundary between the Arabia plate and the Sinai sub-plate. We focus on the Wadi Araba fault, the southernmost segment of the DST. No agreement has been reached yet about the slip rate of the DST. Proposed values vary from 2 to 10 mm/yr. Here, we present results from GPS profiles and measurements of offset geomorphologic features, which ages are comprised between 10 ka and ~300 ka. We installed 17 campaign-style GPS sites distributed along three profiles perpendicular to the fault, with far-field points up to 90 km away from the fault. The sites have been measured twice, in 1999 and 2005, during 48h-long sessions. Campaign data are complemented by data from permanent stations in Israel. Using a locked-fault model, we estimate the present-day slip rate to be 4.9 ± 1.4 mm/yr over 6 years. To estimate the slip rate over longer periods of time, we targeted abandoned alluvial fans offset by the fault at four sites. We mapped and sampled these sites for 10Be cosmogenic dating. At one site, best offset of 48 ± 7 m of a surface dated at 12.1 ± 3.6 ka yields a slip rate of 4.6 ± 2 mm/yr, in very good agreement with the present-day slip rate. Moreover, our morphologic analysis at this site invalidates previous study that suggested a value of 10 mm/yr. At a second site, an offset of 137 ± 7 m of a surface younger than ~50 ka provides a minimum slip rate of 2.6 mm/yr and a larger offset of 598 ± 30 of a surface interpreted to be 93.7 ± 35.4 ka old leads to a slip rate of 7.4 ± 3 mm/yr. The offsets determined at the two other sites, where we obtained ages comprised between 50 to ~300 ka, turned out not to be precise enough to bring new constraints on a Middle to Late Pleistocene time scale. Yet, these results are not inconsistent with previous intervals. Although variations in fault slip rate at the time scale of a few ten

  13. A High shear stress segment along the San Andreas Fault: Inferences based on near-field stress direction and stress magnitude observations in the Carrizo Plain Area

    SciTech Connect

    Castillo, D. A.,; Younker, L.W.

    1997-01-30

    Nearly 200 new in-situ determinations of stress directions and stress magnitudes near the Carrizo plain segment of the San Andreas fault indicate a marked change in stress state occurring within 20 km of this principal transform plate boundary. A natural consequence of this stress transition is that if the observed near-field ``fault-oblique`` stress directions are representative of the fault stress state, the Mohr-Coulomb shear stresses resolved on San Andreas sub-parallel planes are substantially greater than previously inferred based on fault-normal compression. Although the directional stress data and near-hydrostatic pore pressures, which exist within 15 km of the fault, support a high shear stress environment near the fault, appealing to elevated pore pressures in the fault zone (Byerlee-Rice Model) merely enhances the likelihood of shear failure. These near-field stress observations raise important questions regarding what previous stress observations have actually been measuring. The ``fault-normal`` stress direction measured out to 70 km from the fault can be interpreted as representing a comparable depth average shear strength of the principal plate boundary. Stress measurements closer to the fault reflect a shallower depth-average representation of the fault zone shear strength. If this is true, only stress observations at fault distances comparable to the seismogenic depth will be representative of the fault zone shear strength. This is consistent with results from dislocation monitoring where there is pronounced shear stress accumulation out to 20 km of the fault as a result of aseismic slip within the lower crust loading the upper locked section. Beyond about 20 km, the shear stress resolved on San Andreas fault-parallel planes becomes negligible. 65 refs., 15 figs.

  14. The Sparta Fault, Southern Greece: From Segmentation and Tectonic Geomorphology to Seismic Hazard Mapping and Time Dependent Probabilities

    NASA Astrophysics Data System (ADS)

    Papanikolaou, Ioannis; Roberts, Gerald; Deligiannakis, Georgios; Sakellariou, Athina; Vassilakis, Emmanuel

    2013-04-01

    The Sparta Fault system is a major structure approximately 64 km long that bounds the eastern flank of the Taygetos Mountain front (2.407 m) and shapes the present-day Sparta basin. It was activated in 464 B.C., devastating the city of Sparta. This fault is examined and described in terms of its geometry, segmentation, drainage pattern and postglacial throw, emphasizing how these parameters vary along strike. Qualitative analysis of long profile catchments shows a significant difference in longitudinal convexity between the central and both the south and north parts of the fault system, leading to the conclusion of varying uplift rate along strike. Catchments are sensitive in differential uplift as it is observed by the calculated differences of the steepness index ksn between the outer (ksn<83) and central parts (121fault along strike the fault system. Based on fault throw-rates and the bedrock geology a seismic hazard map has been constructed that extracts a locality specific long-term earthquake recurrence record. Based on this map the town of Sparta would experience a destructive event similar to the 464 B.C. approximately every 1792 ± 458 years. Since no other major earthquake M~7.0 has been generated by this system since 464 B.C., a future event could be imminent. As a result, not only time-independent but also time-dependent probabilities, which incorporate the concept of the seismic cycle, have been calculated for the town of Sparta, showing a considerably higher time-dependent probability of 3.0 ± 1.5% over the next 30 years compared to the time-independent probability of 1.66%. Half of the hangingwall area of the Sparta fault can experience intensities ≥IX, but belongs to the lowest category of seismic risk of the national seismic building code. On view of these relatively high calculated probabilities, a reassessment of the building code might be necessary.

  15. The Sparta Fault, Southern Greece: From segmentation and tectonic geomorphology to seismic hazard mapping and time dependent probabilities

    NASA Astrophysics Data System (ADS)

    Papanikolaοu, Ioannis D.; Roberts, Gerald P.; Deligiannakis, Georgios; Sakellariou, Athina; Vassilakis, Emmanuel

    2013-06-01

    The Sparta Fault system is a major structure approximately 64 km long that bounds the eastern flank of the Taygetos Mountain front (2407 m) and shapes the present-day Sparta basin. It was activated in 464 B.C., devastating the city of Sparta. This fault is examined and described in terms of its geometry, segmentation, drainage pattern and post-glacial throw, emphasising how these parameters vary along strike. Qualitative analysis of long profile catchments shows a significant difference in longitudinal convexity between the central and both the south and north parts of the fault system, leading to the conclusion of varying uplift rate along strike. Catchments are sensitive in differential uplift as it is observed by the calculated differences of the steepness index ksn between the outer (ksn < 83) and central parts (121 < ksn < 138) of the Sparta Fault along strike the fault system. Based on fault throw-rates and the bedrock geology a seismic hazard map has been constructed that extracts a locality specific long-term earthquake recurrence record. Based on this map the town of Sparta would experience a destructive event similar to that in 464 B.C. approximately every 1792 ± 458 years. Since no other major earthquake M ~ 7.0 has been generated by this system since 464 B.C., a future event could be imminent. As a result, not only time-independent but also time-dependent probabilities, which incorporate the concept of the seismic cycle, have been calculated for the town of Sparta, showing a considerably higher time-dependent probability of 3.0 ± 1.5% over the next 30 years compared to the time-independent probability of 1.66%. Half of the hanging wall area of the Sparta Fault can experience intensities ≥ IX, but belongs to the lowest category of seismic risk of the national seismic building code. On view of these relatively high calculated probabilities, a reassessment of the building code might be necessary.

  16. History of late Holocene earthquakes at the Willow Creek site on the Nephi segment, Wasatch fault zone, Utah

    USGS Publications Warehouse

    Crone, Anthony J.; Personius, Stephen F.; Duross, Christopher; Machette, Michael N.; Mahan, Shannon

    2014-01-01

    This 43-page report presents new data from the Willow Creek site that provides well-defined and narrow bounds on the times of the three youngest earthquakes on the southern strand of the Nephi segment, Wasatch Fault zone, and refines the time of the youngest earthquake to about 200 years ago. This is the youngest surface rupture on the entire Wasatch fault zone, which occurred about a century or less before European settles arrived in Utah. Two trenches at the Willow Creek site exposed three scarp-derived colluvial wedges that are evidence of three paleoearthquakes. OxCal modeling of ages from Willow Creek indicate that paleoearthquake WC1 occurred at 0.2 ± 0.1 ka, WC2 occurred at 1.2 ± 0.1 ka, and WC3 occurred at 1.9 ± 0.6 ka. Stratigraphic constraints on the time of paleoearthquake WC4 are extremely poor, so OxCal modeling only yields a broadly constrained age of 4.7 ± 1.8 ka. Results from the Willow Creek site significantly refine the times of late Holocene earthquakes on the Southern strand of the Nephi segment, and this result, when combined with a reanalysis of the stratigraphic and chronologic information from previous investigations at North Creek and Red Canyon, yield a stronger basis of correlating individual earthquakes between all three sites.

  17. Effects of Fault Segmentation, Mechanical Interaction, and Structural Complexity on Earthquake-Generated Deformation

    ERIC Educational Resources Information Center

    Haddad, David Elias

    2014-01-01

    Earth's topographic surface forms an interface across which the geodynamic and geomorphic engines interact. This interaction is best observed along crustal margins where topography is created by active faulting and sculpted by geomorphic processes. Crustal deformation manifests as earthquakes at centennial to millennial timescales. Given that…

  18. Fault segmentation, deep rift earthquakes and crustal rheology: Insights from the 2009 Karonga sequence and seismicity in the Rukwa-Malawi rift zone

    NASA Astrophysics Data System (ADS)

    Fagereng, Å.

    2013-08-01

    The Rukwa-Malawi rift zone has a record of seismic events down to depths in excess of 30 km, deep for a zone of active continental extension. This deep seismicity, as well as the presence of long (~ 100 km) border faults, has previously been explained by the long-term bulk rheology of intact, old, cold, anhydrous strong crust in east Africa, or the presence of mafic material in the lower crust. The Karonga sequence of 2009 showed a style of faulting different from continuous slip along long border faults, and is interpreted as segmented failure of hanging wall faults. Coulomb stress transfer in this sequence is calculated, and found to be consistent with segmented slip on a fault system synthetic to a nearby border fault and restricted to depths < 12 km. The inferred thermal structure of the Malawi rift indicates that slip at depths in excess of 30 km occurs at temperatures greater than the 350-450 °C commonly inferred at the base of the seismogenic zone. Crustal strength calculations indicate that long border faults and deep seismicity require the presence of a weak zone of localized deformation with increased strain rate (or fluid pressure), within a strong lower crust. A hypothesis is proposed where shallow, segmented frictional failure occurs in regions of relatively strong, intact crust (e.g. the Karonga sequence), whereas long border faults and deep earthquakes are representative of zones of weakness within strong crust. This hypothesis, if correct, implies that seismogenic thickness can vary within thick elastic lithosphere, such that localized weak zones of the crust enable nucleation of larger seismic events, whereas strong, intact crust favors smaller, segmented events and a shallower seismogenic zone.

  19. Adjacent segment degeneration after single-level anterior cervical decompression and fusion: disc space distraction and its impact on clinical outcomes.

    PubMed

    Li, Jia; Li, Yongqian; Kong, Fanlong; Zhang, Di; Zhang, Yingze; Shen, Yong

    2015-03-01

    The purpose of this study was to find whether excessive distraction of the disc space for cage insertion was a risk factor for adjacent segment degeneration (ASD) after anterior cervical decompression and fusion (ACDF). One hundred and sixteen consecutive patients who underwent ACDF for single-level cervical disc herniation between June 2006 and November 2008 were retrospectively reviewed. Preoperative, postoperative and final follow-up disc height (DH), sagittal segmental alignment (SSA), and sagittal alignment of the cervical spine (SACS) were measured and compared between the ASD group and non-ASD group. In 116 patients, ASD was radiographically proven in 28 (24.1%) patients. The clinical outcomes were significantly improved compared to the preoperative scores in both groups. However, the postoperative and final follow-up DH of the ASD group were significantly higher than in the non-ASD group (p<0.05). In addition, the postoperative DH was significantly correlated with the postoperative or final follow-up SSA (p<0.05). However, postoperative DH was not found to significantly correlate with postoperative or final follow-up SACS (p=0.072 and p=0.096, respectively). Multivariate analysis showed that postoperative DH was the most significant risk factor for ASD. The clinical outcomes of ACDF for single-level degenerative cervical disc disease were satisfactory. Postoperative DH (the distracted distance) had the greatest impact on the incidence of ASD. Excessive disc space distraction is a considerable risk factor for the development of radiographic ASD.

  20. Recurrence of seismic migrations along the central California segment of the San Andreas fault system

    USGS Publications Warehouse

    Wood, M.D.; Allen, S.S.

    1973-01-01

    VERIFICATIONS of tectonic concepts1 concerning seafloor spreading are emerging in a manner that has direct bearing on earthquake prediction. Although the gross pattern of worldwide seismicity contributed to the formulation of the plate tectonic hypothesis, it is the space-time characteristics of this seismicity that may contribute more toward understanding the kinematics and dynamics of the driving mechanism long speculated to originate in the mantle. If the lithosphere is composed of plates that move essentially as rigid bodies, then there should be seismic edge effects associated with this movement. It is these interplate effects, especially seismic migration patterns, that we discuss here. The unidirectional propagation at constant velocity (80 km yr-1 east to west) for earthquakes (M???7.2) on the Antblian fault for the period 1939 to 1956 (ref. 2) is one of the earliest observations of such a phenomenon. Similar studies3,4 of the Alaska Aleutian seismic zone and certain regions of the west coast of South America suggest unidirectional and recurring migrations of earthquakes (M???7.7) occur in these areas. Between these two regions along the great transform faults of the west coast of North America, there is some evidence 5 for unidirectional, constant velocity and recurrent migration of great earthquakes. The small population of earthquakes (M>7.2) in Savage's investigation5 indicates a large spatial gap along the San Andreas system in central California from 1830 to 1970. Previous work on the seismicity of this gap in central California indicates that the recurrence curves remain relatively constant, independent of large earthquakes, for periods up to a century6. Recurrence intervals for earthquakes along the San Andreas Fault have been calculated empirically by Wallace7 on the basis of geological evidence, surface measurements and assumptions restricted to the surficial seismic layer. Here we examine the evidence for recurrence of seismic migrations along

  1. Holocene left-slip rate determined by cosmogenic surface dating on the Xidatan segment of the Kunlun Fault (Qinghai, Chin

    SciTech Connect

    Guoguang, Z; Caffee, M; Finkel, R; G,; demer, Y; Meriaux, A S; Qunlu,; Ryerson, F J; Tapponnier, P; Van der Woerd, J

    1998-09-01

    Cosmogenic dating, using in-situ 26A1 and 10Be in quartz pebbles from alluvial terrace surfaces, constrains the late Holocene slip rate on the Xidatan segment of the Kuniun fault in northeastern Tibet. Two terrace risers offset by 24 ± 3 and 33 f± 4m, having respective ages of 1788 ± 388 and 2914 ± 471 yr, imply a slip rate of 12.1 ± 2.6 mm/yr. The full range of ages obtained ((less than or equal to) 22.8 k.y., most of them between 6.7 and 1.4 k.y.) confirm that terrace deposition and incision, hence landform evolution, are modulated by post-glacial climate change. Coupled with minimum offsets of 9-12 m, this slip rate implies that great earthquakes (M-8) with a recurrence time of 800-1000 yr. rupture the Kunlun fault n

  2. Age of the North Anatolian Fault Segments in the Yalova with U/Th Dating Method by Travertine Data

    NASA Astrophysics Data System (ADS)

    Selim, Haluk; Ömer Taş, K.

    2016-04-01

    Travertine occurrences developed along the segments of the North Anatolian Fault (NAF) in the south of Yalova. Travertines outcrop approximately 1 km2 area. These are middle-thick bedded approximately 20-40 m and back-tilted southward or horizontally. Lithology of travertines deposited such as physolite, stalactites-stalagmites, cave pearls, sharp pebble carbonate nodules, spherical-roller-intricate shapes or laminated banded travertine. Geochemical analyses were performed on the six samples of the travertines. X-ray analysis indicates that all samples are entirely composed of low-Mg calcite. Banded travertines with some tubular structures formed by precipitation from rising hot water are best developed near the toes of the large, hanging-wall-derived alluvial fans, whereas phreatic cement preferentially exists in footwall-derived, alluvial-fan conglomerates. The unit developed clarity which is controlled by normal fault as the structural and morphological, relationship with active tectonics. The travertines are a range-front type. U/Th series age dating results indicate that the travertine deposition extends back to 155 ka and yields ages of 60.000 (± 3, 091) to 153.149 (±13,466) from the range-front type travertines.

  3. Investigating the Electrical Resistivity Structure at the Creeping Segment of the North Anatolian Fault near Ismetpasa by Wide-band Magnetotellurics

    NASA Astrophysics Data System (ADS)

    Tank, Bülent; Kandemir, Özgür; Akbayram, Kenan; Kanar, Fatih; Öztay, Erkan; Rıza Kılıç, Ali; Bakar, Levent; Tok, Turgut; Çobankaya, Mehmet; Aylan, Eşref; Karabulut, Gamze; Paker, Ercan

    2016-04-01

    More than hundred wide-band (360 Hz - 2000 sec.) magnetotelluric (MT) observations were performed and were utilized to decipher the electrical resistivity structure in two- and three- dimensions along a 320 km, northwest - southeast aligned profile that cuts through the Gerede - Ismetpasa segment of the North Anatolian Fault. Even though Gerede - Ismetpasa region has accommodated 1944, Gerede (Mw=7.2) and 1951, Kursunlu (Mw=6.9) events, seismically, this segment is considered as a relatively quiet portion of the North Anatolian Fault and is well known with its creeping behavior (approx. 7.6 mm/yr). In this study the aim is to compare electrical resistivity structure with the creep information. Several modeling attempts targeting different depths and portions of the profile were made for imaging different problems. Preliminary three-dimensional models that were developed by WSINV3DMT suggest that; (i) There is significant and deep extending fault zone conductor that might be related with the creeping segment and (ii) In the deeper levels high and low conductivity interfaces are present in and around the fault region, which might be related to the North Anatolian Fault and seldom earthquake activity.

  4. New High-Resolution 3D Imagery of Fault Deformation and Segmentation of the San Onofre and San Mateo Trends in the Inner California Borderlands

    NASA Astrophysics Data System (ADS)

    Holmes, J. J.; Driscoll, N. W.; Kent, G. M.; Bormann, J. M.; Harding, A. J.

    2015-12-01

    The Inner California Borderlands (ICB) is situated off the coast of southern California and northern Baja. The structural and geomorphic characteristics of the area record a middle Oligocene transition from subduction to microplate capture along the California coast. Marine stratigraphic evidence shows large-scale extension and rotation overprinted by modern strike-slip deformation. Geodetic and geologic observations indicate that approximately 6-8 mm/yr of Pacific-North American relative plate motion is accommodated by offshore strike-slip faulting in the ICB. The farthest inshore fault system, the Newport-Inglewood Rose Canyon (NIRC) fault complex is a dextral strike-slip system that extends primarily offshore approximately 120 km from San Diego to the San Joaquin Hills near Newport Beach, California. Based on trenching and well data, the NIRC fault system Holocene slip rate is 1.5-2.0 mm/yr to the south and 0.5-1.0 mm/yr along its northern extent. An earthquake rupturing the entire length of the system could produce an Mw 7.0 earthquake or larger. West of the main segments of the NIRC fault complex are the San Mateo and San Onofre fault trends along the continental slope. Previous work concluded that these were part of a strike-slip system that eventually merged with the NIRC complex. Others have interpreted these trends as deformation associated with the Oceanside Blind Thrust fault purported to underlie most of the region. In late 2013, we acquired the first high-resolution 3D P-Cable seismic surveys (3.125 m bin resolution) of the San Mateo and San Onofre trends as part of the Southern California Regional Fault Mapping project aboard the R/V New Horizon. Analysis of these volumes provides important new insights and constraints on the fault segmentation and transfer of deformation. Based on the new 3D sparker seismic data, our preferred interpretation for the San Mateo and San Onofre fault trends is they are transpressional features associated with westward

  5. The Incidence of Adjacent Segment Breakdown in Polysegmental Thoracolumbar Fusions of Three or More Levels with Minimum 5-Year Follow-up

    PubMed Central

    Abraham, Edward P.; Manson, Neil A.; McKeon, Melissa D.

    2014-01-01

    Study Design Retrospective cohort study. Objective To identify the incidence of adjacent segment pathology (ASP) after thoracolumbar fusion of three or more levels, the risk factors for the development of ASP, and the need for further surgical intervention in this particular patient population. Methods A retrospective analysis of a prospective surgical database identified 217 patients receiving polysegmental (≥ 3 levels) spinal fusion with minimum 5-year follow-up. Risk factors were evaluated, and the following data were obtained from the review of radiographs and charts: radiographic measures—levels fused, fusion status, presence of ASP; clinical measures—patient assessment, Oswestry Disability Index (ODI), and the need for further surgery. Results The incidence of radiographic ASP (RASP) was 29%; clinical or symptomatic ASP (CASP), 18%; and those requiring surgery, 9%. Correlation was observed between ODI and ASP, symptomatic ASP, and need for revision surgery. Age, preoperative degenerative diagnosis, and absence of fusion demonstrated significant association to ASP. Conclusions ASP was observed in a significant number of patients receiving polysegmental fusion of three or more levels. ODI scores correlated to RASP, CASP, and the need for revision surgery. PMID:25072002

  6. The Incidence of Adjacent Segment Breakdown in Polysegmental Thoracolumbar Fusions of Three or More Levels with Minimum 5-Year Follow-up.

    PubMed

    Abraham, Edward P; Manson, Neil A; McKeon, Melissa D

    2014-06-01

    Study Design Retrospective cohort study. Objective To identify the incidence of adjacent segment pathology (ASP) after thoracolumbar fusion of three or more levels, the risk factors for the development of ASP, and the need for further surgical intervention in this particular patient population. Methods A retrospective analysis of a prospective surgical database identified 217 patients receiving polysegmental (≥ 3 levels) spinal fusion with minimum 5-year follow-up. Risk factors were evaluated, and the following data were obtained from the review of radiographs and charts: radiographic measures-levels fused, fusion status, presence of ASP; clinical measures-patient assessment, Oswestry Disability Index (ODI), and the need for further surgery. Results The incidence of radiographic ASP (RASP) was 29%; clinical or symptomatic ASP (CASP), 18%; and those requiring surgery, 9%. Correlation was observed between ODI and ASP, symptomatic ASP, and need for revision surgery. Age, preoperative degenerative diagnosis, and absence of fusion demonstrated significant association to ASP. Conclusions ASP was observed in a significant number of patients receiving polysegmental fusion of three or more levels. ODI scores correlated to RASP, CASP, and the need for revision surgery.

  7. Palaeoseismology of the Vilariça segment of the Manteigas-Bragança fault in northeastern Portugal

    USGS Publications Warehouse

    Rockwell, Thomas; Fonseca, Joao; Madden, Chris; Dawson, Tim; Owen, Lewis A.; Vilanova, Susana; Figueiredo, Paula

    2009-01-01

    The Manteigas-Bragança fault is a major, 250-km-long, NNE-striking, sinistral strike-slip structure in northern Portugal. This fault has no historical seismicity for large earthquakes, although it may have generated moderate (M5+) earthquakes in 1751 and 1858. Evidence of continued left horizontal displacement is shown by the presence of Cenozoic pull-apart basins as well as late Quaternary stream deflections. To investigate its recent slip history, a number of trenches were excavated at three sites along the Vilariça segment, north and south of the Douro River. At one site at Vale Meão winery, the occurrence of at least two and probably three events in the past 14.5 ka was determined, suggesting an average return period of about 5–7 ka. All three events appear to have occurred as a cluster in the interval between 14.5 and 11 ka, or shortly thereafter, suggesting a return period of less than 2 ka between events within the cluster. In the same area, a small offset rill suggests 2–2.5 m of slip in the most recent event and about 6.1 m after incision below a c. 16 ka alluvial fill event along the Douro River. At another site along the Vilariça River alluvial plain, NE of the Vale Meão site, several trenches were excavated in late Pleistocene and Holocene alluvium, and exposed the fault displacing channel deposits dated to between 18 and 23 ka. In a succession of closely spaced parallel cuts and trenches, the channel riser was traced into and across the fault to resolve c. 6.5 m of displacement after 18 ka and c. 9 m of slip after c. 23 ka. These observations yield a slip rate of 0.3–0.5 mm/a, which is consistent with earlier estimates. Combining the information on timing at Vale Meão winery and displacement at Vilariça argues for earthquakes in the M7+ range, with coseismic displacements of 2–3 m. This demonstrates that there are potential seismic sources in Portugal that are not associated with the 1755 Lisbon earthquake or the Tagus Valley, and

  8. Integration of paleoseismic data from multiple sites to develop an objective earthquake chronology: Application to the Weber segment of the Wasatch fault zone, Utah

    USGS Publications Warehouse

    DuRoss, Christopher B.; Personius, Stephen F.; Crone, Anthony J.; Olig, Susan S.; Lund, William R.

    2011-01-01

    We present a method to evaluate and integrate paleoseismic data from multiple sites into a single, objective measure of earthquake timing and recurrence on discrete segments of active faults. We apply this method to the Weber segment (WS) of the Wasatch fault zone using data from four fault-trench studies completed between 1981 and 2009. After systematically reevaluating the stratigraphic and chronologic data from each trench site, we constructed time-stratigraphic OxCal models that yield site probability density functions (PDFs) of the times of individual earthquakes. We next qualitatively correlated the site PDFs into a segment-wide earthquake chronology, which is supported by overlapping site PDFs, large per-event displacements, and prominent segment boundaries. For each segment-wide earthquake, we computed the product of the site PDF probabilities in common time bins, which emphasizes the overlap in the site earthquake times, and gives more weight to the narrowest, best-defined PDFs. The product method yields smaller earthquake-timing uncertainties compared to taking the mean of the site PDFs, but is best suited to earthquakes constrained by broad, overlapping site PDFs. We calculated segment-wide earthquake recurrence intervals and uncertainties using a Monte Carlo model. Five surface-faulting earthquakes occurred on the WS at about 5.9, 4.5, 3.1, 1.1, and 0.6 ka. With the exception of the 1.1-ka event, we used the product method to define the earthquake times. The revised WS chronology yields a mean recurrence interval of 1.3 kyr (0.7–1.9-kyr estimated two-sigma [2δ] range based on interevent recurrence). These data help clarify the paleoearthquake history of the WS, including the important question of the timing and rupture extent of the most recent earthquake, and are essential to the improvement of earthquake-probability assessments for the Wasatch Front region.

  9. Integration of paleoseismic data from multiple sites to develop an objective earthquake chronology: Application to the Weber segment of the Wasatch fault zone, Utah

    USGS Publications Warehouse

    DuRoss, C.B.; Personius, S.F.; Crone, A.J.; Olig, S.S.; Lund, W.R.

    2011-01-01

    We present a method to evaluate and integrate paleoseismic data from multiple sites into a single, objective measure of earthquake timing and recurrence on discrete segments of active faults. We apply this method to the Weber segment (WS) of the Wasatch fault zone using data from four fault-trench studies completed between 1981 and 2009. After systematically reevaluating the stratigraphic and chronologic data from each trench site, we constructed time-stratigraphic OxCal models that yield site probability density functions (PDFs) of the times of individual earthquakes. We next qualitatively correlated the site PDFs into a segment-wide earthquake chronology, which is supported by overlapping site PDFs, large per-event displacements, and prominent segment boundaries. For each segment-wide earthquake, we computed the product of the site PDF probabilities in common time bins, which emphasizes the overlap in the site earthquake times, and gives more weight to the narrowest, best-defined PDFs. The product method yields smaller earthquake-timing uncertainties compared to taking the mean of the site PDFs, but is best suited to earthquakes constrained by broad, overlapping site PDFs. We calculated segment-wide earthquake recurrence intervals and uncertainties using a Monte Carlo model. Five surface-faulting earthquakes occurred on the WS at about 5.9, 4.5, 3.1, 1.1, and 0.6 ka. With the exception of the 1.1-ka event, we used the product method to define the earthquake times. The revised WS chronology yields a mean recurrence interval of 1.3 kyr (0.7-1.9-kyr estimated two-sigma [2??] range based on interevent recurrence). These data help clarify the paleoearthquake history of the WS, including the important question of the timing and rupture extent of the most recent earthquake, and are essential to the improvement of earthquake-probability assessments for the Wasatch Front region.

  10. Constraining Basin Geometry and Fault Kinematics on the Santo Tomas Segment of the Agua Blanca Fault Through a Combined Geophysical and Structural Study

    NASA Astrophysics Data System (ADS)

    Springer, A.; Wetmore, P.; Fletcher, J.; Connor, C. B.; Callihan, S.; Beeson, J.; Wilson, J.

    2008-12-01

    The Santo Tomas basin, located in northern Baja California, formed at a right step in the dextral Agua Blanca fault (ABF). The ABF extends for more than 120km east from Punta Banda, with an east-west strike, and represents the southernmost fault in the San Andreas system of faulting. The basin is located roughly 40km south of Ensenada where the Agua Blanca fault intersects the Maximos fault. A detailed geophysical analysis defines the basin geometry, and helps to constrain the distribution and offset of mapped and concealed faults. Geophysical and structural data sets are combined to constrain the kinematic evolution of the Santo Tomas basin, including determining the relative amount of dip-slip and strike-slip motion on basin-bounding faults. Gravity data was collected over seven transects across and along the axis of the basin at 500 meter intervals, with 200 meter intervals at locations of known or inferred faults. Magnetic data were taken over the same lines, and are used in conjunction with gravity data to constrain the locations, geometries and displacements of intrabasinal faults. The combined gravity and magnetic data are modeled using Geosoft Oasis montaj software to create 2 3/4D models along profiles across the study area. Modeling of the geophysical data combined with structural mapping indicates that the Santo Tomas basin is bound by two major strike-slip faults, the ABF on the northeastern side and the Maximos fault on south, Based on offset markers, most of the strike-slip motion appears to be concentrated on the ABF on the north side of the basin. The ABF fault is characterized by multiple subparallel fault strands that appear to coalesce into single strands to the northwest and southeast of the basin. The Maximos is characterized by a single strand throughout the basin and it exhibits a minor dip-slip component. Basin sediments thicken slightly against the Maximos fault to as much as 1km. A third fault, cutting across the basin southeast of the

  11. Macroseismological And Paleoseismological Studies In The Active Segments Of The Morelia Acambay Fault System, Mexico

    NASA Astrophysics Data System (ADS)

    Garduño-Monroy, V. H.; Rodriguez-Pascua, M. A.; Israde-Alcantara, I.; Hernandez-Madrigal, V. M.

    2007-05-01

    Paleoseismological studies along several faults of the Morelia-Acambay system show clear evidence of its seismicity. In the Acambay region, four seismic events were identified during the Pliocene Pleistocene; two linked to large sub aquatic landslides, and two to liquefaction processes. The two seismic events associated to slumps were also recognized in the Ixtlahuaca, Mexico, region; meaning these were relevant seismic events at a regional level. Their magnitudes were above 5 degrees. Because these latter events are located in the same column, they could be of aid in knowing recurrence periods. In the southern portion of the Lake of Patzcuaro region a collapse was identified generating a rock avalanche nearly 29,000 years ago. This collapse is associated to an earthquake of magnitude above 7 degrees, which decreased the lake's extension and resulted in morphology of small hummocks. The Purhepecha term Jaracuaro means "place that emerges" and is the name of a former island where Pre Hispanic settlements occurred. The island is exclusively made up of lacustrine sequences that rose above 50m in height, georadar and vertical electrical signal (VES) studies do not reveal intrusive bodies associated to this deformation. Isosists of the 1845 and 1858 seismic events were reconstructed in the modified Mercalli scale through several historical studies in a number of municipalities in the State of Michoacan. The results indicate isosistes of IX degrees in Patzcuaro, where the earthquake caused the collapse of the basilica. During the 1858 earthquake the water level in the southern portion of the Lake of Patzcuaro raised over 2m and the destruction of 120 adobe houses is related to the generation of a tsunami. This seismic event is being characterized in wells and ditches dugs around Patzcuaro Lake. The region of Patzcuaro has experienced a number of magmatic and tectonic events that undoubtedly modified the conditions of the lake regarding its sedimentology and anthropogenic

  12. Fault kinematics and tectonic stress in the seismically active Manyara Dodoma Rift segment in Central Tanzania Implications for the East African Rift

    NASA Astrophysics Data System (ADS)

    Macheyeki, Athanas S.; Delvaux, Damien; De Batist, Marc; Mruma, Abdulkarim

    2008-07-01

    The Eastern Branch of the East African Rift System is well known in Ethiopia (Main Ethiopian Rift) and Kenya (Kenya or Gregory Rift) and is usually considered to fade away southwards in the North Tanzanian Divergence, where it splits into the Eyasi, Manyara and Pangani segments. Further towards the south, rift structures are more weakly expressed and this area has not attracted much attention since the mapping and exploratory works of the 1950s. In November 4, 2002, an earthquake of magnitude Mb = 5.5 struck Dodoma, the capital city of Tanzania. Analysis of modern digital relief, seismological and geological data reveals that ongoing tectonic deformation is presently affecting a broad N-S trending belt, extending southward from the North Tanzanian Divergence to the region of Dodoma, forming the proposed "Manyara-Dodoma Rift segment". North of Arusha-Ngorongoro line, the rift is confined to a narrow belt (Natron graben in Tanzania) and south of it, it broadens into a wide deformation zone which includes both the Eyasi and Manyara grabens. The two-stage rifting model proposed for Kenya and North Tanzania also applies to the Manyara-Dodoma Rift segment. In a first stage, large, well-expressed topographic and volcanogenic structures were initiated in the Natron, Eyasi and Manyara grabens during the Late Miocene to Pliocene. From the Middle Pleistocene onwards, deformations related to the second rifting stage propagated southwards to the Dodoma region. These young structures have still limited morphological expressions compared to the structures formed during the first stage. However, they appear to be tectonically active as shown by the high concentration of moderate earthquakes into earthquake swarms, the distribution of He-bearing thermal springs, the morphological freshness of the fault scarps, and the presence of open surface fractures. Fault kinematic and paleostress analysis of geological fault data in basement rocks along the active fault lines show that recent

  13. Structure of the 1906 near-surface rupture zone of the San Andreas Fault, San Francisco Peninsula segment, near Woodside, California

    USGS Publications Warehouse

    Rosa, C.M.; Catchings, R.D.; Rymer, M.J.; Grove, Karen; Goldman, M.R.

    2016-01-01

    nearby sites. Multiple fault strands in the area of the 1906 surface rupture may account for variations in geologic slip rates calculated from several paleoseismic sites along the Peninsula segment of the San Andreas Fault.t.

  14. Structure of the 1906 near-surface rupture zone of the San Andreas Fault, San Francisco Peninsula segment, near Woodside, California

    USGS Publications Warehouse

    Rosa, C.M.; Catchings, R.D.; Rymer, M.J.; Grove, Karen; Goldman, M.R.

    2016-07-08

    nearby sites. Multiple fault strands in the area of the 1906 surface rupture may account for variations in geologic slip rates calculated from several paleoseismic sites along the Peninsula segment of the San Andreas Fault.t.

  15. Monitoring Creep Movement with Terrestrial LIDAR on the Gerede - Bayramören Segment of the North Anatolian Fault Zone, Turkey

    NASA Astrophysics Data System (ADS)

    Altınok Erayık, Sevgi; Altunel, Erhan; Tunçel, Esra; Çaǧlar Yalçıner, Cahit

    2016-04-01

    The North Anatolian Fault Zone (NAFZ) accommodates the westward motion of the Anatolian block relative to Eurasian plate with a slip rate of about 20 mm/yr. The Gerede - Bayramören Segment of the NAFZ ruptured during the 1944 Gerede (M:7.2) earthquake. In early 1970s, some deformations were realized on the Gerede - Bayramören Segment of the NAFZ and attributed to aseismic creep. Since then different techniques have been using to understand the nature of the creep. In order to understand the length of the creeping section and the relationship between seismic activity and creep rate, eight new stations were constructed along the Gerede - Bayramören Segment and were monitored by terrestrial LIDAR. Stations were monitored periodically since May 2013. Periodical measurements showed that the aseismic creep is going on between Gerede in west and Bayramören in east, for a distance of about 80 km. Present results showed that the creep rate changes between 2 - 6 ±1 mm/yr along the Gerede Bayramören segment of the NAFZ. Considering the slip rate on the NAFZ, this segment of the NAFZ is still capable of generating large earthquakes since at least 2/3 of the yearly slip still accumulates on the fault.

  16. Surface Rupture Segmentation and Slip Distribution of the 14 November 2001 Ms 8.1 Earthquake on the Kunlun Fault, Qinghai-Tibetan Plateau, China

    NASA Astrophysics Data System (ADS)

    Ding, G.; Chen, J.; Chen, Y.; Tian, Q.; Wang, Z.; Shan, X.; Ren, J.; Zhao, R.; Wang, Z.

    2004-12-01

    The 14 November 2001 Ms =8.1 earthquake represent the most recent one of a series of large earthquakes along the Kunlun Fault, a highly active left-lateral strike-slip fault that bound the northern Tibet Plateau. Detailed surface rupture mapping, including 291 surficial left-lateral slip measurements and 111 net vertical slip measurements shows that the surface trace was 426 km long, multisegmented and consists of five major segments: the Taiyanghu, Buka Daban, Kusaihu West, Kusaihu East, and Kunlun Pass fault segments with the maximum left-lateral slip magnitudes 3, 5.7, 6, 6.4, and 4.2 m from west to east respectively, averaging 2.7 m. Two primary characteristics of the surface rupture are the en echelon geometry of the principle faults and the predominance of left-lateral strike slip, with local components of normal and reverse displacements caused by local changes in the fault geometry. Transtensional and transpressional structures were observed within releasing and restraining step-over areas respectively. The vertical slip components on all faults are less than 1 m (with as much as of 5.1 m vertical slip), quite variable and show little systematic behavior. Sinistral surficial slip was quite variable along the main trace of the rupture, however there is fairly regular long-wavelength (tens to hundreds of kilometers) behavior to the east of the Buka Daban Feng. Slips as large as 5~6 meters were observed at 5~6 sites that distributed at different surface rupture segments with the asymmetric shape of the slip profiles, which may be reflective of the direction rupture propagated. In additional, field and satellite images evidence indicates that most of the faults that ruptured in 2001 had had late Quaternary displacement. The variations in surficial slip (at both short and long length scales) which is only near-field slip using tape measures, should be considered minimum values and represent real variations in the amount of brittle slip on visible fractures at

  17. Paleoseismology of the Nephi Segment of the Wasatch Fault Zone, Juab County, Utah - Preliminary Results From Two Large Exploratory Trenches at Willow Creek

    USGS Publications Warehouse

    Machette, Michael N.; Crone, Anthony J.; Personius, Stephen F.; Mahan, Shannon; Dart, Richard L.; Lidke, David J.; Olig, Susan S.

    2007-01-01

    In 2004, we identified a small parcel of U.S. Forest Service land at the mouth of Willow Creek (about 5 km west of Mona, Utah) that was suitable for trenching. At the Willow Creek site, which is near the middle of the southern strand of the Nephi segment, the WFZ has vertically displaced alluvial-fan deposits >6-7 m, forming large, steep, multiple-event scarps. In May 2005, we dug two 4- to 5-m-deep backhoe trenches at the Willow Creek site, identified three colluvial wedges in each trench, and collected samples of charcoal and A-horizon organic material for AMS (acceleration mass spectrometry) radiocarbon dating, and sampled fine-grained eolian and colluvial sediment for luminescence dating. The trenches yielded a stratigraphic assemblage composed of moderately coarse-grained fluvial and debris-flow deposits and discrete colluvial wedges associated with three faulting events (P1, P2, and P3). About one-half of the net vertical displacement is accommodated by monoclinal tilting of fan deposits on the hanging-wall block, possibly related to massive ductile landslide deposits that are present beneath the Willow Creek fan. The timing of the three surface-faulting events is bracketed by radiocarbon dates and results in a much different fault chronology and higher slip rates than previously considered for this segment of the Wasatch fault zone.

  18. Compilation of selected faults and lineaments that may be relevant to a study of seismic activity in southern Nevada and part of adjacent California

    SciTech Connect

    Bucknam, R.C.

    1983-02-01

    The enclosed preliminary map shows selected prominent faults and regional topographic lineaments that may be relevant to a study of known or potential seismic activity in the California-southern Nevada region surrounding the Nevada Test Site.

  19. The 1995 Mw 7.2 Gulf of Aqaba Earthquake revisited: Identifying active fault segments by joint inversion of geodetic and teleseismic data

    NASA Astrophysics Data System (ADS)

    Bathke, H.; Feng, G.; Heimann, S.; Jonsson, S.; Mai, P. M.; Nikkhoo, M.

    2015-12-01

    The largest earthquakes in Saudi Arabia occur at the northwestern boundary of the Arabian plate on a system of left-lateral transform faults extending from the Red Sea in the South and North through the Gulf of Aqaba. The last major earthquake along this boundary occurred in November 1995 and in a complex tectonic setting offshore in the Gulf of Aqaba, consisting of several transform faults and pull-apart basins. Various authors have studied this earthquake in the past, either by using geodetic radar (InSAR) or teleseismic (P and S waves) data, and several source models of the earthquake rupture and the active fault segments have been proposed. However, these source models differ significantly from each other and it still remains unclear which fault segments within the Gulf were activated during the event. There are various reasons for these differences. Teleseismic data alone cannot locate the event well, whereas the lack of near field co-seismic displacement data (due to the event's offshore location) and the quasi north-south oriented strike-slip faulting of the earthquake result in a low SNR in the radar data. Consequently, the uncertainties of inferred model parameters are large and have not been properly estimated so far. In this work, we use radar data from two additional tracks that have not been used before, which provides a more complete displacement field of the earthquake. By using multiple aperture radar interferometry it is possible to better constrain the south-north oriented strike-slip component. In addition, we include both the geodetic data and the teleseismic data in a joint inversion setup allowing combining the strengths of each dataset to constrain the model parameters. By including the full data-variance covariance-matrixes in Bayesian inference sampling, we estimate the model-uncertainties and the related range of likely source models. Consequently, we re-evaluate, which fault segments were activated during the earthquake in the Gulf of

  20. Vertical deformation of lacustrine shorelines along breached relay ramps, Catlow Valley fault, southeastern Oregon, USA

    NASA Astrophysics Data System (ADS)

    Hopkins, Michael C.; Dawers, Nancye H.

    2016-04-01

    Vertical deformation of pluvial lacustrine shorelines is attributed to slip along the Catlow Valley fault, a segmented Basin and Range style normal fault in southeastern Oregon, USA. The inner edges of shorelines are mapped along three breached relay ramps along the fault to examine the effect of fault linkage on the distribution of slip. Shoreline inner edges act as paleohorizontal datums so deviations in elevation from horizontal, outside of a 2 m error window, are taken to be indications of fault slip. The sites chosen represent a spectrum of linkage scenarios in that the throw on the linking fault compared to that on the main fault adjacent to the linking fault varies from site to site. Results show that the maturity of the linkage between segments (i.e. larger throw on the linking fault with respect to the main fault) does not control the spatial distribution of shoreline deformation. Patterns of shoreline deformation indicate that the outboard, linking, and/or smaller ramp faults have slipped since the shorelines formed. Observations indicate that displacement has not fully localized on the linking faults following complete linkage between segments.

  1. Deep-fault connection characterization from combined field and geochemical methodology; examples from Green River and Haiti fault systems

    NASA Astrophysics Data System (ADS)

    Nadine, E. Z.; Frery, E.; Leroy, S.; Mercier De Lepinay, B. F.; Momplaisir, R.

    2011-12-01

    Fault transfer properties are depending on different parameters, such as fault plane geometry, regional to local offset guiding the morphology through time, but are also very sensitive on other factors which may vary through time and space. Detailed along-strike observations and analyses of the Green River Fault system (Utah) outline the strong impact of several parameters; pre-existing structures or basement heterogeneities, lateral variation of the host-rock mechanical properties, the change of paleostress field through time which creates complex fault intersections. This last parameter, is often associated either with along-and-across fluid drainage (fault leaking) or with abnormal sealing deformation and uplifts corresponding to the locked fault segments. Along the Green River anticline, which is dissected by Salt wash and Little Grand wash major faults, several leaking segments are distributed. They have been analysed for geochemical characterization. In fact, carbon dioxide rich waters expelled from natural or artificial (well-driven geyser) springs, are located preferentially at structural intersection points. Changes in fault transfer properties has been proved as discontinuous from detailed datings (U/Th datings: see Frery et al AGU 2011 this meeting) on the top-fault travertines precipitation. The correlation with fault mineralisation at depth is still under investigation. In this area, not considered as very seismic one compared to the adjacent Basin and Ranges area, fault activity relates both on slow processes indicating a long seismic recurrence time, and on local reservoir short-time de-pressurisation processes. The same methods of investigation will be used on the very active Haitian fault system. The new constraints applied on the Enriquillo-Plantain-garden Fault (EPGF) responsible for the initial deep tectonic stress release (12 January 2010), have not been expressed by a clear surface fault rupture (surface locked segment), but by a northward

  2. Origin of narrow terranes and adjacent major terranes occurring along the denali fault in the eastern and central alaska range, alaska

    USGS Publications Warehouse

    Nokleberg, W.J.; Richter, D.H.

    2007-01-01

    Several narrow terranes occur along the Denali fault in the Eastern and Central Alaska Range in Southern Alaska. These terranes are the Aurora Peak, Cottonwood Creek, Maclaren, Pingston, and Windy terranes, and a terrane of ultramafic and associated rocks. Exterior to the narrow terranes to the south is the majorWrangellia island arc composite terrane, and to the north is the major Yukon Tanana metamorphosed continental margin terrane. Overlying mainly the northern margin of the Wrangellia composite terrane are the Kahiltna overlap assemblage to the west, and the Gravina- Nutzotin-Gambier volcanic-plutonic- sedimentary belt to the east and southeast. The various narrow terranes are interpreted as the result of translation of fragments of larger terranes during two major tectonic events: (1) Late Jurassic to mid-Cretaceous accretion of the Wrangellia island arc composite terrane (or superterrane composed of the Wrangellia, Peninsular, and Alexander terranes) and associated subduction zone complexes; and (2) starting in about the Late Cretaceous, dextral transport of the Wrangellia composite terrane along the Denali fault. These two major tectonic events caused: (1) entrapment of a lens of oceanic lithosphere along the suture belt between the Wrangellia composite terrane and the North American Craton Margin and outboard accreted terranes to form the ultramafic and mafic part of the terrane of ultramafic and associated rocks, (2) subsequent dextral translation along the Denali fault of the terrane of ultramafic and associated rocks, (3) dextral translation along the Denali fault of the Aurora Peak, Cottonwood Creek, and Maclaren and continental margin arc terranes from part of the Coast plutonic-metamorphic complex (Coast-North Cascade plutonic belt) in the southwest Yukon Territory or Southeastern Alaska, (4) dextral translation along the Denali fault of the Pingston passive continental margin from a locus along the North American Continental Margin, and (5

  3. Scaling, kinematics and evolution of a polymodal fault system: Hail Creek Mine, NE Australia

    NASA Astrophysics Data System (ADS)

    Carvell, Jacob; Blenkinsop, Thomas; Clarke, Gavin; Tonelli, Maurizio

    2014-09-01

    We analyse a system of normal faults that cuts sandstone, siltstone, mudstone, coal, and tuff at Hail Creek Coal Mine in the Bowen Basin, NE Australia. Our detailed mapping utilised the dense borehole network and strip mining operations. The fault surfaces have complex geometries, yet the components of the individual faults show similar orientation variability to the whole fault system. The faults and their components dip to the SE, NW, NNW, and SSE with an orthorhombic symmetry that we refer to as polymodal. There are multiple displacement peaks, with complementary changes on adjacent faults. This observation suggests kinematic coherence between neighbouring faults. Twin displacement peaks on some faults suggest that segment linkage occurred on a scale of hundreds of m. These polymodal faults follow the same displacement-length scaling laws as other normal faults. Fault dip is affected by lithology, with steeper dips in more competent (sandstone) beds. An ‘odd-axis’ construction using whole fault planes suggests that they formed in a triaxial strain state (three different principal strains) with vertical shortening, and horizontal extension along principal directions of 148° and 058°. Odd-axis constructions using individual fault components, as opposed to whole faults, give similar principal strain orientations and maximum strain ratios. The variable component orientations, and the consistency of fault kinematics on different scales, suggest that the faults evolved by the propagation or linkage of smaller components with variable orientations, within the same bulk strain state.

  4. Imaging the complexity of an active normal fault system: The 1997 Colfiorito (central Italy) case study

    USGS Publications Warehouse

    Chiaraluce, L.; Ellsworth, W.L.; Chiarabba, C.; Cocco, M.

    2003-01-01

    Six moderate magnitude earthquakes (5 < Mw < 6) ruptured normal fault segments of the southern sector of the North Apennine belt (central Italy) in the 1997 Colfiorito earthquake sequence. We study the progressive activation of adjacent and nearby parallel faults of this complex normal fault system using ???1650 earthquake locations obtained by applying a double-difference location method, using travel time picks and waveform cross-correlation measurements. The lateral extent of the fault segments range from 5 to 10 km and make up a broad, ???45 km long, NW trending fault system. The geometry of each segment is quite simple and consists of planar faults gently dipping toward SW with an average dip of 40??-45??. The fault planes are not listric but maintain a constant dip through the entire seismogenic volume, down to 8 km depth. We observe the activation of faults on the hanging wall and the absence of seismicity in the footwall of the structure. The observed fault segmentation appears to be due to the lateral heterogeneity of the upper crust: preexisting thrusts inherited from Neogene's compressional tectonic intersect the active normal faults and control their maximum length. The stress tensor obtained by inverting the six main shock focal mechanisms of the sequence is in agreement with the tectonic stress active in the inner chain of the Apennine, revealing a clear NE trending extension direction. Aftershock focal mechanisms show a consistent extensional kinematics, 70% of which are mechanically consistent with the main shock stress field.

  5. Geoelectrical behavior of a Fault Zone: the meaning of the electrical resistivity of metric-scale segments of the Liquiñe-Ofqui and the Arc-oblique Long-lived Fault Systems, Southern Andes

    NASA Astrophysics Data System (ADS)

    Roquer, T.; Arancibia, G.; Yanez, G. A.; Estay, N.; Rowland, J. V.; Figueroa, R.; Iturrieta, P. C.

    2015-12-01

    The geoelectrical behavior of blind fault zones has been studied by different authors at decametric-to-kilometric scales, and inferred to reveal the dimensions of the main structural domains of a fault zone (core vs. damage zone). However, there is still a lack in the application of electrical methods in exposed fault zones, despite the importance of validating the inferences based on electrical measurements with direct geologic observation. In this study we correlate the results of structural mapping and geoelectrical measurements in two metric-scale, very well exposed segments of the Liquiñe-Ofqui Fault System (LOFS) and the Arc-oblique Long-lived Fault System (ALFS), Southern Andes. The LOFS is an active dextral and dextral-normal ca. 1200-km-long Cenozoic intra-arc structure that strikes NNE to NE. Although the LOFS and the ALFS cross-cut each other, the ALFS is an apparently older basement NW-striking fault system where mainly sinistral movement is recorded. Two 22-m-long transects were mapped revealing in both examples a simple core and an assymetric damage zone with more frequency of fractures in the hanging wall than in the footwall. The LOFS outcrop showed a WNW-striking, 65°S-dipping core; the ALFS, a NW-striking, 60°SW-dipping core. A 2D direct-current electrical survey was made at each locality, orthogonal to the respective strike of the core. The field installation of the electrical survey used two electrode configurations for each outcrop: (1) electrodes were put in a vertical wall of rock, which gives a resistivity profile in plan view; and (2) electrodes were put in the ground, which gives a cross-section resistivity profile. The combined structural and electrical results suggest that: (1) it is possible to discriminate the geoelectrical response of the main metric-scale structural domains: the core and the fractured damage zones are relative conductors (20-200 ohm-m), whereas the less fractured damage zones are relative resistive volumes (500

  6. Kinematic links between the Eastern Mosha Fault and the North Tehran Fault, Alborz range, northern Iran

    NASA Astrophysics Data System (ADS)

    Ghassemi, Mohammad R.; Fattahi, Morteza; Landgraf, Angela; Ahmadi, Mehdi; Ballato, Paolo; Tabatabaei, Saeid H.

    2014-05-01

    Kinematic interaction of faults is an important issue for detailed seismic hazard assessments in seismically active regions. The Eastern Mosha Fault (EMF) and the North Tehran Fault (NTF) are two major active faults of the southern central Alborz mountains, located in proximity of Tehran (population ~ 9 million). We used field, geomorphological and paleoseismological data to explore the kinematic transition between the faults, and compare their short-term and long-term history of activity. We introduce the Niknamdeh segment of the NTF along which the strike-slip kinematics of EMF is transferred onto the NTF, and which is also responsible for the development of a pull-apart basin between the eastern segments of the NTF. The Ira trench site at the linkage zone between the two faults reveals the history of interaction between rock avalanches, active faulting and sag-pond development. The kinematic continuity between the EMF and NTF requires updating of seismic hazard models for the NTF, the most active fault adjacent to the Tehran Metropolis. Study of offsets of large-scale morphological features along the EMF, and comparison with estimated slip rates along the fault indicates that the EMF has started its left-lateral kinematics between 3.2 and 4.7 Ma. According to our paleoseismological data and the morphology of the nearby EMF and NTF, we suggest minimum and maximum values of about 1.8 and 3.0 mm/year for the left-lateral kinematics on the two faults in their linkage zone, averaged over Holocene time scales. Our study provides a partial interpretation, based on available data, for the fault activity in northeastern Tehran region, which may be completed with studies of other active faults of the region to evaluate a more realistic seismic hazard analysis for this heavily populated major city.

  7. Geologic map of the Bartlett Springs Fault Zone in the vicinity of Lake Pillsbury and adjacent areas of Mendocino, Lake, and Glenn Counties, California

    USGS Publications Warehouse

    Ohlin, Henry N.; McLaughlin, Robert J.; Moring, Barry C.; Sawyer, Thomas L.

    2010-01-01

    The Lake Pillsbury area lies in the eastern part of the northern California Coast Ranges, along the east side of the transform boundary between the Pacific and North American plates (fig. 1). The Bartlett Springs Fault Zone is a northwest-trending zone of faulting associated with this eastern part of the transform boundary. It is presently active, based on surface creep (Svarc and others, 2008), geomorphic expression, offset of Holocene units (Lienkaemper and Brown, 2009), and microseismicity (Bolt and Oakeshott, 1982; Dehlinger and Bolt, 1984; DePolo and Ohlin, 1984). Faults associated with the Bartlett Springs Fault Zone at Lake Pillsbury are steeply dipping and offset older low to steeply dipping faults separating folded and imbricated Mesozoic terranes of the Franciscan Complex and interleaved rocks of the Coast Range Ophiolite and Great Valley Sequence. Parts of this area were mapped in the late 1970s and 1980s by several investigators who were focused on structural relations in the Franciscan Complex (Lehman, 1978; Jordan, 1975; Layman, 1977; Etter, 1979). In the 1980s the U.S. Geological Survey (USGS) mapped a large part of the area as part of a mineral resource appraisal of two U.S. Forest Service Roadless areas. For evaluating mineral resource potential, the USGS mapping was published at a scale of 1:62,500 as a generalized geologic summary map without a topographic base (Ohlin and others, 1983; Ohlin and Spear, 1984). The previously unpublished mapping with topographic base is presented here at a scale of 1:30,000, compiled with other mapping in the vicinity of Lake Pillsbury. The mapping provides a geologic framework for ongoing investigations to evaluate potential earthquake hazards and structure of the Bartlett Springs Fault Zone. This geologic map includes part of Mendocino National Forest (the Elk Creek Roadless Area) in Mendocino, Glenn, and Lake Counties and is traversed by several U.S. Forest Service Routes, including M1 and M6 (fig. 2). The study

  8. Study of fault slip modes

    NASA Astrophysics Data System (ADS)

    Adushkin, V. V.; Kocharyan, G. G.; Novikov, V. A.

    2016-09-01

    We present the data of the laboratory experiments on studying the regularities of gradual transition from the stick-slip behavior to aseismic creeping on the interblock boundary. The experiments show that small variations in the material composition in the principal slip zones of the faults may cause a significant change in the fraction of seismic energy radiated during the dynamic unloading of the adjacent segment of the rock mass. The experiments simulate interblock sliding regimes with the values of the scaled kinetic energy differing by a few orders of magnitude and relatively small distinctions in the strength of the contacts and in the amplitude of the released shear stresses. The results of the experiments show that the slip mode and the fraction of the deformation energy that goes into the seismic radiation are determined by the ratio of two parameters—the stiffness of the fault and the stiffness of the enclosing rock mass. An important implication of the study for solving the engineering tasks is that for bringing a stressed segment of a fault or a crack into a slip mode with low-intensity radiation of seismic energy, the anthropogenic impact should be aimed at diminishing the stiffness of the fault zone rather than at releasing the excessive stresses.

  9. Source mechanisms of dike-induced earthquakes in the Dabbahu-Manda Hararo rift segment in Afar, Ethiopia: implications for faulting above dikes

    NASA Astrophysics Data System (ADS)

    Belachew, Manahloh; Ebinger, C.; Coté, D.

    2013-03-01

    The process of dike emplacement changes the stress field in the intruded region, causing swarms of migrating earthquakes. We determine source mechanisms of the largest earthquakes (ML ≥ 3.5) induced by the emplacement of two large volume dikes along an incipient seafloor spreading segment in Afar, Ethiopia to determine their space-time relations. Given the possibility of complex source mechanisms during dike emplacement, we solved for four different source models: double couple (DC), DC + isotropic (DC + ISO), deviatoric (DVMT), and full moment tensor (FMT). The solutions obtained using the different models indicate that the earthquakes have non-double couple components. The best double-couple mechanisms, which are mainly normal faulting with small strike-slip components, have slip planes nearly perpendicular to the geodetically determined plate opening direction. Most of these earthquakes are low-frequency earthquakes with peak frequencies ≤2 Hz, and they occurred during the propagation phase of the dikes. The space-time distribution of the source mechanisms with respect to the migrating patterns of seismicity during dike emplacement, the shallow source depths estimated, the lack of mechanisms with ˜90º rotated P-axes from the regional maximum compressive stress and the non-double couple nature of the mechanisms indicate that the largest magnitude earthquakes are generated mainly by normal faulting above the dikes probably with some component of tensile opening under the influence of dike-related fluids. These observations suggest that normal faulting above dikes is the main process of seismic energy release during dike intrusions. Assuming that faults above dikes follow length-displacement relations found for tectonic earthquakes, total seismic slips of 0.8 m and 1.3 m are estimated for the November 2007 and October 2008 dikes, respectively. Similarity of the total slip estimates from the largest earthquakes and from elastic dislocation model estimates of

  10. Fault kinematics of the Magallanes-Fagnano fault system, southern Chile; an example of diffuse strain and sinistral transtension along a continental transform margin

    NASA Astrophysics Data System (ADS)

    Betka, Paul; Klepeis, Keith; Mosher, Sharon

    2016-04-01

    A system of left-lateral faults that separates the South American and Scotia plates, known as the Magallanes-Fagnano fault system, defines the modern tectonic setting of the southernmost Andes and is superimposed on the Late Cretaceous - Paleogene Patagonian fold-thrust belt. Fault kinematic data and crosscutting relationships from populations of thrust, strike-slip and normal faults from Peninsula Brunswick adjacent to the Magallanes-Fagnano fault system, presented herein, show kinematic and temporal relationships between thrust faults and sets of younger strike-slip and normal faults. Thrust fault kinematics are homogeneous in the study area and record subhorizontal northeast-directed shortening. Strike-slip faults record east-northeast-directed horizontal shortening, west-northwest-directed horizontal extension and form Riedel and P-shear geometries compatible with left-lateral slip on the main splay of the Magallanes-Fagnano fault system. Normal faults record north-south trending extension that is compatible with the strike-slip faults. The study area occurs in a releasing step-over between overlapping segments of the Magallanes-Fagnano fault system, which localized on antecedent sutures between basement terranes with differing geological origin. Results are consistent with regional tectonic models that suggest sinistral shearing and transtension in the southernmost Andes was contemporaneous with the onset of seafloor spreading in the Western Scotia Sea during the Early Miocene.

  11. 3D Dynamic Rupture Simulation Across a Complex Fault System: the Mw7.0, 2010, Haiti Earthquake

    NASA Astrophysics Data System (ADS)

    Douilly, R.; Aochi, H.; Calais, E.; Freed, A. M.

    2013-12-01

    Earthquakes ruptures sometimes take place on a secondary fault and surprisingly do not activate an adjacent major one. The 1989 Loma Prieta earthquake is a classic case where rupture occurred on a blind thrust while the adjacent San Andreas Fault was not triggered during the process. Similar to Loma Prieta, the Mw7.0, January 12 2010, Haiti earthquake also ruptured a secondary blind thrust, the Léogâne fault, adjacent to the main plate boundary, the Enriquillo Plantain Garden Fault, which did not rupture during this event. Aftershock relocalizations delineate the Léogâne rupture with two north dipping segments with slightly different dip, where the easternmost segment had mostly dip-slip motion and the westernmost one had mostly strike-slip motion. In addition, an offshore south dipping structure inferred from the aftershocks to the west of the rupture zone coincides with the offshore Trois Baies reverse fault, a region of increase in Coulomb stress increase. In this study, we investigate the rupture dynamics of the Haiti earthquake in a complex fault system of multiple segments identified by the aftershock relocations. We suppose a background stress regime that is consistent with the type of motion of each fault and with the regional tectonic regime. We initiate a nucleation on the east segment of the Léogâne fault by defining a circular region with a 2 km radius where shear stress is slightly greater than the yield stress. By varying friction on faults and background stress, we find a range of plausible scenarios. In the absence of near-field seismic records of the event, we score the different models against the static deformation field derived from GPS and InSAR at the surface. All the plausible simulations show that the rupture propagates from the eastern to the western segment along the Léogâne fault, but not on the Enriquillo fault nor on the Trois Baies fault. The best-fit simulation shows a significant increase of shear stresses on the Trois Baies

  12. Holocene and latest Pleistocene paleoseismology of the Salt Lake City segment of the Wasatch Fault Zone, Utah, at the Penrose Drive Trench Site

    USGS Publications Warehouse

    DuRoss, Christopher B.; Hylland, Michael D.; McDonald, Greg N.; Crone, Anthony J.; Personius, Stephen F.; Gold, Ryan D.; Mahan, Shannon

    2014-01-01

    The Salt Lake City segment (SLCS) of the Wasatch fault zone (WFZ) and the West Valley fault zone (WVFZ) compromise Holocene-active normal faults that bound a large intrabasin graben in northern Salt Lake Valley and have evidence of recurrent, large-magnitude (M ~6-7) surface-faulting earthquakes. However, at the time of this investigation, questions remained regarding the timing, displacement, and recurrence of latest Pleistocene and Holocene earthquakes on the northern SLCS and WVFZ , and whether the WVFZ is seismically independent of, or moves coseismically with, the SLCS. To improve paleoseismic data for the SLCS, we conducted a fault-trench investigation at the Penrose Drive site on the northern SLCS. Two trenches, excavated across an 11-m-high scarp near the northern end of the East Bench fault, exposed colluvial-wedge evidence for fize of six (preferred) surface-faulting earthquakes postdating to Provo-phase shoreline of Lake Bonneville (~14-18 ka). Radiocarbon and luminescence ages support earthquake times at 4.0 ± 0.5 ka (2σ) (PD1), 5.9 ± 0.7 ka (PD2), 7.5 ± 0.8 ka (PD3a), 9.7 ± 1.1 ka (PD3b), 10.9 ± 0.2 ka (PD4), and 12.1 ± 1.6 ka (PD5). At least one additional earthquake occurred at 16.5 ± 1.9 ka (PD6) based on an erosional unconformity that separates deformed Lake Bonneville sily and flat-lying Provo-phase shoreline gravel. Earthquakes PD5-PD1 yield latest Pleistocene (post-Provo) and Holocene mean recurrence intervals of ~1.6 kyr and ~1.7-1.9 kyr, respectively. Using 1.0-1.4 m of per-event vertical displacement for PD5-PD3b corroborate previously identified SLCS earthquakes at 4-10 ka. PD4 and PD5 occurred within an ~8-kyr *17-9 ka) time interval on the SLCS previously interpreted as a period of seismic quiescence, and PD6 possibly corresponds with a previously identified earthquake at ~17 ka (although both events have large timing uncertainties). The Penrose data, when combined with previous paleoseismic results, improve the latest Pleistocene

  13. The SCEC 3D Community Fault Model (CFM-v5): An updated and expanded fault set of oblique crustal deformation and complex fault interaction for southern California

    NASA Astrophysics Data System (ADS)

    Nicholson, C.; Plesch, A.; Sorlien, C. C.; Shaw, J. H.; Hauksson, E.

    2014-12-01

    Southern California represents an ideal natural laboratory to investigate oblique deformation in 3D owing to its comprehensive datasets, complex tectonic history, evolving components of oblique slip, and continued crustal rotations about horizontal and vertical axes. As the SCEC Community Fault Model (CFM) aims to accurately reflect this 3D deformation, we present the results of an extensive update to the model by using primarily detailed fault trace, seismic reflection, relocated hypocenter and focal mechanism nodal plane data to generate improved, more realistic digital 3D fault surfaces. The results document a wide variety of oblique strain accommodation, including various aspects of strain partitioning and fault-related folding, sets of both high-angle and low-angle faults that mutually interact, significant non-planar, multi-stranded faults with variable dip along strike and with depth, and active mid-crustal detachments. In places, closely-spaced fault strands or fault systems can remain surprisingly subparallel to seismogenic depths, while in other areas, major strike-slip to oblique-slip faults can merge, such as the S-dipping Arroyo Parida-Mission Ridge and Santa Ynez faults with the N-dipping North Channel-Pitas Point-Red Mountain fault system, or diverge with depth. Examples of the latter include the steep-to-west-dipping Laguna Salada-Indiviso faults with the steep-to-east-dipping Sierra Cucapah faults, and the steep southern San Andreas fault with the adjacent NE-dipping Mecca Hills-Hidden Springs fault system. In addition, overprinting by steep predominantly strike-slip faulting can segment which parts of intersecting inherited low-angle faults are reactivated, or result in mutual cross-cutting relationships. The updated CFM 3D fault surfaces thus help characterize a more complex pattern of fault interactions at depth between various fault sets and linked fault systems, and a more complex fault geometry than typically inferred or expected from

  14. Seismicity and Faulting in an Urbanized area: Flagstaff, Arizona

    NASA Astrophysics Data System (ADS)

    Brumbaugh, D. S.

    2013-12-01

    Flagstaff, Arizona is a community of more than 60,000 and lies in an area of active tectonism. Well documented evidence exists of geologically recent volcanism and fault related seismicity. The urban area is located within a volcanic field that is considered active and the area is also the locus of numerous fault systems, some of whose members are considered to be potentially active. This suggestion of active faulting and seismicity for the area is supported by the recent 1993 Mw 5.3 Cataract Creek earthquake. Chief concern for Flagstaff is focused upon the Anderson Mesa fault which has a mapped surface length of 40 kilometers with the north end extending into the city limits of Flagstaff. A worse case scenario for rupture along the entire length of the fault would be the occurrence of an Mw 6.9 earthquake. The slip rate for this fault is low, however it is not well determined due to a lack of Neogene or Quaternary deposits. The historic record of seismicity adjacent to the surface expression of the Anderson Mesa fault includes two well recorded earthquake swarms (1979,2011) as well as other individual events over this time period all of which are of M< 4.0. The epicentral locations of these events are of interest with respect to the fault geometry which shows four prominent segments: North, Central, South, Ashurst. All of the historic events are located within the central segment. This distribution can be compared to evidence available for the orientation of regional stresses. The focal mechanism for the 1993 Mw 5.3 Cataract Creek earthquake shows a northwest striking preferred slip surface with a trend (300) parallel to that of the Central segment of the Anderson Mesa fault (300-305). The other three fault segments of the Anderson Mesa fault have north-south trends. The seismicity of the Central segment of the fault suggests that slip on this segment may occur in the future. Given the length of this segment a MCE event could be as large as Mw 6.3.

  15. Spreading rate dependence of gravity anomalies along oceanic transform faults.

    PubMed

    Gregg, Patricia M; Lin, Jian; Behn, Mark D; Montési, Laurent G J

    2007-07-12

    Mid-ocean ridge morphology and crustal accretion are known to depend on the spreading rate of the ridge. Slow-spreading mid-ocean-ridge segments exhibit significant crustal thinning towards transform and non-transform offsets, which is thought to arise from a three-dimensional process of buoyant mantle upwelling and melt migration focused beneath the centres of ridge segments. In contrast, fast-spreading mid-ocean ridges are characterized by smaller, segment-scale variations in crustal thickness, which reflect more uniform mantle upwelling beneath the ridge axis. Here we present a systematic study of the residual mantle Bouguer gravity anomaly of 19 oceanic transform faults that reveals a strong correlation between gravity signature and spreading rate. Previous studies have shown that slow-slipping transform faults are marked by more positive gravity anomalies than their adjacent ridge segments, but our analysis reveals that intermediate and fast-slipping transform faults exhibit more negative gravity anomalies than their adjacent ridge segments. This finding indicates that there is a mass deficit at intermediate- and fast-slipping transform faults, which could reflect increased rock porosity, serpentinization of mantle peridotite, and/or crustal thickening. The most negative anomalies correspond to topographic highs flanking the transform faults, rather than to transform troughs (where deformation is probably focused and porosity and alteration are expected to be greatest), indicating that crustal thickening could be an important contributor to the negative gravity anomalies observed. This finding in turn suggests that three-dimensional magma accretion may occur near intermediate- and fast-slipping transform faults. PMID:17625563

  16. Spreading rate dependence of gravity anomalies along oceanic transform faults.

    PubMed

    Gregg, Patricia M; Lin, Jian; Behn, Mark D; Montési, Laurent G J

    2007-07-12

    Mid-ocean ridge morphology and crustal accretion are known to depend on the spreading rate of the ridge. Slow-spreading mid-ocean-ridge segments exhibit significant crustal thinning towards transform and non-transform offsets, which is thought to arise from a three-dimensional process of buoyant mantle upwelling and melt migration focused beneath the centres of ridge segments. In contrast, fast-spreading mid-ocean ridges are characterized by smaller, segment-scale variations in crustal thickness, which reflect more uniform mantle upwelling beneath the ridge axis. Here we present a systematic study of the residual mantle Bouguer gravity anomaly of 19 oceanic transform faults that reveals a strong correlation between gravity signature and spreading rate. Previous studies have shown that slow-slipping transform faults are marked by more positive gravity anomalies than their adjacent ridge segments, but our analysis reveals that intermediate and fast-slipping transform faults exhibit more negative gravity anomalies than their adjacent ridge segments. This finding indicates that there is a mass deficit at intermediate- and fast-slipping transform faults, which could reflect increased rock porosity, serpentinization of mantle peridotite, and/or crustal thickening. The most negative anomalies correspond to topographic highs flanking the transform faults, rather than to transform troughs (where deformation is probably focused and porosity and alteration are expected to be greatest), indicating that crustal thickening could be an important contributor to the negative gravity anomalies observed. This finding in turn suggests that three-dimensional magma accretion may occur near intermediate- and fast-slipping transform faults.

  17. The cysteine-rich region of raf-1 kinase contains zinc, translocates to liposomes, and is adjacent to a segment that binds GTP-ras.

    PubMed

    Ghosh, S; Xie, W Q; Quest, A F; Mabrouk, G M; Strum, J C; Bell, R M

    1994-04-01

    Different domains of the serine/threonine kinase, raf-1, were expressed as fusion proteins with glutathione S-transferase (GST) in Escherichia coli and purified to near homogeneity by affinity chromatography. A cysteine-rich domain of raf-1 was found to contain 2 mol of zinc (molar basis), similar to analogous cysteine-rich domains of protein kinase C. GST-fusion proteins, containing the cysteine-rich domain of raf-1, bound to liposomes in a phosphatidylserine-dependent manner. In contrast to protein kinase C, the translocation of raf-1 was not dependent upon diacylglycerol, phorbol ester, or calcium, nor did raf-1 bind phorbol esters. A GST-fusion protein encoding residues 1-147 of raf-1 bound to normal GTP-ras with high affinity, but not to mutant GTP-Ala35 ras; no binding was detected to GDP-ras. The binding of a smaller fusion protein (residues 1-130 of raf-1) was about 10-fold weaker, inferring that a 17-amino acid sequence represents a critical binding determinant in intact raf-1. These residues are adjacent to the amino-terminal end of, and partially extend into, the cysteine-rich domain (amino acids 139-184). A synthetic peptide corresponding to this 17-amino acid sequence blocked the interaction of raf-1 with ras. The function of the cysteine-rich region of raf-1 homologous to protein kinase C is to promote translocation of raf-1 kinase to membranes and to form part of the high affinity binding site for GTP-ras.

  18. The Growth of Simple Mountain Ranges: 2. Geomorphic Evolution at Fault Linkage Sites

    NASA Astrophysics Data System (ADS)

    Dawers, N. H.; Densmore, A. L.; Davis, A. M.; Gupta, S.

    2002-12-01

    Large normal faults grow partly through linkage of fault segments and partly by fault tip propagation. The process by which fault segments interact and link is critical to understanding how topography is created along fault-bounded ranges. Structural studies and numerical models have shown that fault linkage is accompanied by localised increased displacement rate, which in turn drives rapid base level fall at the evolving range front. The changes in both along-strike fault structure and base level are most pronounced at and adjacent to sites of fault linkage. These areas, known as relay zones, thus preserve clues to both the tectonic history and the geomorphic evolution of large fault-bounded mountain ranges. We discuss the temporal and spatial constraints on the evolution of footwall-range topography, by comparing a number of active fault linkage sites, using field and DEM observations of the spatial pattern of footwall denudation. In particular, we focus on sites in Pleasant Valley, Nevada (Pearce and Tobin fault segments) and in the northeastern Basin and Range (the Beaverhead fault, Idaho, and the Star Valley fault, Wyoming). The study areas represent different stages in the structural and geomorphic evolution of relay zones, and allow us to propose a developmental model of large fault evolution and landscape response. Early in the growth of fault segments into an overlapping geometry, catchments may form within the evolving relay. However, increasing displacement rate associated with fault interaction and linkage makes these catchments prone to capture by streams that have incised headward from the range front. This scenario leads to locally increased footwall denudation in the vicinity of the capture site. Longitudinal profiles of streams differ with respect to position along relays and whether or not any particular stream has been able to capture early-formed drainages. The restricted space between interacting en echelon fault segments helps preserve close

  19. Multi-parameter analysis of seismoturbidites in the Kumburgaz Basin of Sea of Marmara: Implications for creeping versus locked Central High segment of the North Anatolian Fault

    NASA Astrophysics Data System (ADS)

    Yakupoǧlu, Nurettin; Uçarkuş, Gülsen; Eriş, K. Kadir; Çaǧatay, M. Namık; Henry, Pierre; Yalamaz, Burak; Sabuncu, Asen; Acar, Dursun

    2016-04-01

    Sediment sequences deposited in active transform basins provide valuable archives of earthquake-triggered co-seismic sedimentation. A better understanding of the relationship between offshore fault ruptures and Seismoturbidites would have direct implications for earthquake hazard assessment. Submerged section of the North Anatolian Fault in the northern Sea of Marmara basin, which experienced more than 55 (Ms>6.8) earthquakes in the last 2000 years, poses a unique laboratory to study such kind of sync-tectonic history. Following the devastating 1999 Izmit and Duzce earthquakes (Mw = 7.4/7.2 respectively), a major seismic gap is now along the offshore branch of the NAF in the Sea of Marmara. The segments that control the Cinarcik and Kumburgaz basins in the Sea of Marmara have not ruptured during the 20th century. This study focusses on the Kumburgaz basin, which is located along the central segment of the NAF, and its less-known linkage to historical earthquakes, particularly to Ms>7 1509 and 1766 earthquakes. The main objective of this study is to test the two alternative hypotheses of a creeping versus locked central High segment by determining the frequency and timing of earthquake triggered turbidite units in the Kumburgaz basin. A 21-m-long piston core recovered in Kumburgaz basin during the Marsite cruise in 2014 is analysed at high resolution in order to identify the discrete turbidite-homogenite units (T-H units). The piston core reveals 22 T-H units where several packages consist of a sharp basal contact and multiple fining upward beds of sand to coarse silt as characteristically seen in most Seismoturbidite units. We initiated a systematic study of T-H units with the objectives of establishing criteria for identification of Seismoturbidites by analysing the physical, mineralogical and chemical composition of the piston core. The density and magnetic susceptibility changes along the core are analysed by Multi-Sensor Core Logger (MSCL). High detrital input

  20. Development of Land Segmentation, Stream-Reach Network, and Watersheds in Support of Hydrological Simulation Program-Fortran (HSPF) Modeling, Chesapeake Bay Watershed, and Adjacent Parts of Maryland, Delaware, and Virginia

    USGS Publications Warehouse

    Martucci, Sarah K.; Krstolic, Jennifer L.; Raffensperger, Jeff P.; Hopkins, Katherine J.

    2006-01-01

    The U.S. Geological Survey, U.S. Environmental Protection Agency Chesapeake Bay Program Office, Interstate Commission on the Potomac River Basin, Maryland Department of the Environment, Virginia Department of Conservation and Recreation, Virginia Department of Environmental Quality, and the University of Maryland Center for Environmental Science are collaborating on the Chesapeake Bay Regional Watershed Model, using Hydrological Simulation Program - FORTRAN to simulate streamflow and concentrations and loads of nutrients and sediment to Chesapeake Bay. The model will be used to provide information for resource managers. In order to establish a framework for model simulation, digital spatial datasets were created defining the discretization of the model region (including the Chesapeake Bay watershed, as well as the adjacent parts of Maryland, Delaware, and Virginia outside the watershed) into land segments, a stream-reach network, and associated watersheds. Land segmentation was based on county boundaries represented by a 1:100,000-scale digital dataset. Fifty of the 254 counties and incorporated cities in the model region were divided on the basis of physiography and topography, producing a total of 309 land segments. The stream-reach network for the Chesapeake Bay watershed part of the model region was based on the U.S. Geological Survey Chesapeake Bay SPARROW (SPAtially Referenced Regressions On Watershed attributes) model stream-reach network. Because that network was created only for the Chesapeake Bay watershed, the rest of the model region uses a 1:500,000-scale stream-reach network. Streams with mean annual streamflow of less than 100 cubic feet per second were excluded based on attributes from the dataset. Additional changes were made to enhance the data and to allow for inclusion of stream reaches with monitoring data that were not part of the original network. Thirty-meter-resolution Digital Elevation Model data were used to delineate watersheds for each

  1. Tectonic evolution of 200 km of Mid-Atlantic Ridge over 10 million years: Interplay of volcanism and faulting

    NASA Astrophysics Data System (ADS)

    Cann, Johnson R.; Smith, Deborah K.; Escartin, Javier; Schouten, Hans

    2015-07-01

    We reconstruct the history of the mode of accretion of an area of the Mid-Atlantic Ridge south of the Kane fracture zone using bathymetric morphology. The area includes 200 km of the spreading axis and reaches to 10 Ma on either side. We distinguish three tectonic styles: (1) volcanic construction with eruption and intrusion of magma coupled with minor faulting, (2) extended terrain with abundant large-offset faults, (3) detachment faulting marked by extension on single long-lived faults. Over 40% of the seafloor is made of extended terrain and detachment faults. The area includes products of seven spreading segments. The spreading axis has had detachment faulting or extended terrain on one or both sides for 70% of the last 10 Ma. In some parts of the area, regions of detachment faulting and extended terrain lie close to segment boundaries. Regions of detachment faulting initiated at 10 Ma close to the adjacent fracture zones to the north and south, and then expanded away from them. We discuss the complex evidence from gravity, seismic surveys, and bathymetry for the role of magma supply in generating tectonic style. Overall, we conclude that input of magma at the spreading axis has a general control on the development of detachment faulting, but the relationship is not strong. Other factors may include a positive feedback that stabilizes detachment faulting at the expense of volcanic extension, perhaps through the lubrication of active detachment faults by the formation of low friction materials (talc, serpentine) on detachment fault surfaces.

  2. Seismic Structure of the Endeavour Segment, Juan de Fuca Ridge: Correlations of Crustal Magma Chamber Properties With Seismicity, Faulting, and Hydrothermal Activity

    NASA Astrophysics Data System (ADS)

    van Ark, E. M.; Detrick, R. S.; Canales, J. P.; Carbotte, S. M.; Diebold, J. B.; Harding, A.; Kent, G.; Nedimovic, M. R.; Wilcock, W. S.

    2003-12-01

    Multichannel seismic reflection data collected in July 2002 at the RIDGE2000 Integrated Studies Site at the Endeavour segment, Juan de Fuca Ridge show a high-amplitude, mid-crustal reflector underlying all of the known hydrothermal vent fields at this segment. This reflector, which has been identified with a crustal magma body [Detrick et al., 2002], is found at a two-way travel time of 0.85-1.5 s (1.9-4.0 km) below the seafloor and extends approximately 25 km along axis although it is only 1-2 km wide on the cross-axis lines. The reflector is shallowest (2.5 km depth on the along-axis line) beneath the central, elevated part of the Endeavour segment and deepens toward the segment ends, with a maximum depth of 4 km. The cross axis lines show the mid-crustal reflector dipping from 9 to 50? to the east with the shallowest depths under the ridge axis and greater depths under the eastern flank of the ridge. The amplitude-offset behavior of this mid-crustal axial reflector is consistent with a negative impedance contrast, indicating the presence of melt or a crystallizing mush. We have constructed partial offset stacks at 2-3 km offset to examine the variation of melt-mush content of the axial magma chamber along axis. We see a decrease in P-wave amplitudes with increasing offset for the mid-crustal reflector beneath the Mothra and Main Endeavour vent fields and between the Salty Dawg and Sasquatch vent fields, indicating the presence of a melt-rich body. Beneath the High Rise, Salty Dawg, and Sasquatch vent fields P-wave amplitudes vary little with offset suggesting the presence of a more mush-rich magma chamber. Hypocenters of well-located microseismicity in this region [Wilcock et al., 2002] have been projected onto the along-axis and cross-axis seismic lines, revealing that most axial earthquakes are concentrated in a depth range of 1.5 - 2.7 km, just above the axial magma chamber. In general, seismicity is distributed diffusely within this zone indicating thermal

  3. Imaging fault slip variation along the central San Andreas fault from satellite, airborne InSAR and GPS

    NASA Astrophysics Data System (ADS)

    Liu, Z.; Lundgren, P.; Fielding, E. J.; Hensley, S.

    2011-12-01

    The improved spatiotemporal resolution of surface deformation from recent satellite and airborne InSAR measurements provides great potential to improve our understanding of faulting processes and earthquake hazard for a given fault system. A major plate boundary fault in central California, the central San Andreas fault (CSAF) displays a spectrum of complex fault slip behaviors with creeping in its central segment that decreases towards its northwest and southeast ends where the fault transitions to being locked. In the north the CSAF branches into two sub-parallel faults that are both actively accommodating plate motion. To the south, near the Parkfield transition, large earthquakes have occurred with at least six Mw ~6.0 events since 1857, most recently in 2004. To understand the complexity and variety of fault slip behaviors and fault mechanics, we integrate satellite and airborne synthetic aperture radar (SAR) repeat pass interferometry (RPI) observations, with GPS measurements from the Plate Boundary Observatory (PBO) and regional campaign networks to estimate fault slip and shallow slip deficits along the CSAF. Existing C-band ERS-1/2, Envisat and Radarsat SAR data provide long archives of SAR data over the region but are subject to severe decorrelation. The Japan Aerospace Exploration Agency's ALOS satellite has made less frequent acquisitions (5-6/yr per track) since 2006 but its PALSAR L-band sensor provides much improved coherence compared to shorter wavelength radar data. More recently, the NASA UAVSAR airborne SAR has repeated fault perpendicular adjacent swaths imaged from opposing look directions and fault parallel swath flights over the CSAF over the past three years and provides an improved imaging of fault slip related deformation at finer spatial resolution than previous platforms (~6m at 12 azimuth x 3 range looks). Compared to C-band instruments, the UAVSAR provides nearly complete spatial coverage. Compared to the ALOS mission, the UAVSAR

  4. Electrical Structure of the Creeping San Andreas Fault at Hollister, California

    NASA Astrophysics Data System (ADS)

    Bedrosian, P. A.; Unsworth, M. J.; Egbert, G.; Thurber, C.

    2001-12-01

    Individual segments of the San Andreas Fault (SAF) exhibit markedly different patterns of seismicity ranging from locked to creeping. The factors controlling such variation are not well understood, but could include fault geometry, geology, and the presence or absence of fault-zone fluids. Magnetotelluric data have been used to image the geoelectric structure of the San Andreas Fault zone and surrounding areas in an attempt to understand the distribution and role of fault-zone fluids. Previous surveys have studied the locked Carrizo segment and the transitional Parkfield segment. This study has been extended to consider creeping segments of the San Andreas and Calaveras Faults. Magnetotelluric data were collected in 1999 along two profiles near Paicines and Bear Valley, with continuous coverage within 1-2 km of the faults. Robust time-series processing and a non-linear conjugate gradient algorithm were employed to produce models of the electrical structure of the fault-zone. The features of the model required by the data include: 1) A highly resistive body southwest of the SAF, adjacent to the SAF with a near-vertical contact. This unit is coincident with the Gabilan granites. 2) A broad zone of enhanced electrical conductivity is imaged between the San Andreas and Calaveras Faults. Discrete shallow regions of high conductivity are coincident with the San Andreas and Calaveras Faults. 3) A prominent fault-zone conductor (FZC) is imaged down to at least 8 km depth. This zone has a (horizontally-integrated) conductance of 600 Siemens, similar in magnitude to that observed at Parkfield. The upper to mid-crustal depths of these conductive zones suggest that they are due to the presence of saline fluids, since nearby wells have encountered brines at depths of several hundred meters. Additionally, seismic tomographic studies image a zone of decreased Vp and enhanced Poisson's ratio which is essentially coincident with the imaged zone of high conductivity beneath the

  5. Three-dimensional dynamic rupture simulations across interacting faults: The Mw7.0, 2010, Haiti earthquake

    NASA Astrophysics Data System (ADS)

    Douilly, R.; Aochi, H.; Calais, E.; Freed, A. M.

    2015-02-01

    The mechanisms controlling rupture propagation between fault segments during a large earthquake are key to the hazard posed by fault systems. Rupture initiation on a smaller fault sometimes transfers to a larger fault, resulting in a significant event (e.g., 2002 M7.9 Denali USA and 2010 M7.1 Darfield New Zealand earthquakes). In other cases rupture is constrained to the initial fault and does not transfer to nearby faults, resulting in events of more moderate magnitude. This was the case of the 1989 M6.9 Loma Prieta and 2010 M7.0 Haiti earthquakes which initiated on reverse faults abutting against a major strike-slip plate boundary fault but did not propagate onto it. Here we investigate the rupture dynamics of the Haiti earthquake, seeking to understand why rupture propagated across two segments of the Léogâne fault but did not propagate to the adjacent Enriquillo Plantain Garden Fault, the major 200 km long plate boundary fault cutting through southern Haiti. We use a finite element model to simulate propagation of rupture on the Léogâne fault, varying friction and background stress to determine the parameter set that best explains the observed earthquake sequence, in particular, the ground displacement. The two slip patches inferred from finite fault inversions are explained by the successive rupture of two fault segments oriented favorably with respect to the rupture propagation, while the geometry of the Enriquillo fault did not allow shear stress to reach failure.

  6. Exhumation history of an active fault to constrain a fault-based seismic hazard scenario: the Pizzalto fault (central Apennines, Italy) example.

    NASA Astrophysics Data System (ADS)

    Tesson, Jim; Pace, Bruno; Benedetti, Lucilla; Visini, Francesco; Delli Rocioli, Mattia; Didier, Bourles; Karim, keddadouche; Gorges, Aumaitre

    2016-04-01

    A prerequisite to constrain fault-based and time-dependent earthquake rupture forecast models is to acquire data on the past large earthquake frequency on an individual seismogenic source and to compare all the recorded occurrences in the active fault-system. We investigated the Holocene seismic history of the Pizzalto normal fault, a 13 km long fault segment belonging to the Pizzalto-Rotella-Aremogna fault system in the Apennines (Italy). We collected 44 samples on the Holocene exhumed Pizzalto fault plane and analyzed their 36Cl and rare earth elements content. Conjointly used, the 36Cl and REE concentrations show that at least 6 events have exhumed 4.4 m of the fault scarp between 3 and 1 ka BP, the slip per event ranging from 0.3 to 1.2 m. No major events have been detected over the last 1 ka. The Rotella-Aremogna-Pizzalto fault system has a clustered earthquake behaviour with a mean recurrence time of 1.2 ka and a low to moderate probability (ranging from 4% to 26%) of earthquake occurrence over the next 50 years. We observed similarities between seismic histories of several faults belonging to two adjacent fault systems. This could again attest that non-random processes occurring in the release of the strain accumulated on faults, commonly referred to as fault interactions and leading to apparent synchronization. If these processes were determined as being the main parameter controlling the occurrence of earthquakes, it would be crucial to take them into account in seismic hazard models.

  7. Late Holocene earthquake history of the Brigham City segment of the Wasatch fault zone at the Hansen Canyon, Kotter Canyon, and Pearsons Canyon trench sites, Box Elder County, Utah

    USGS Publications Warehouse

    DuRoss, Christopher B.; Personius, Stephen F.; Crone, Anthony J.; McDonald, Greg N.; Briggs, Richard W.

    2012-01-01

    Of the five central segments of the Wasatch fault zone (WFZ) having evidence of recurrent Holocene surface-faulting earthquakes, the Brigham City segment (BCS) has the longest elapsed time since its most recent surface-faulting event (~2.1 kyr) compared to its mean recurrence time between events (~1.3 kyr). Thus, the BCS has the highest time-dependent earthquake probability of the central WFZ. We excavated trenches at three sites––the Kotter Canyon and Hansen Canyon sites on the north-central BCS and Pearsons Canyon site on the southern BCS––to determine whether a surface-faulting earthquake younger than 2.1 ka occurred on the BCS. Paleoseismic data for Hansen Canyon and Kotter Canyon confirm that the youngest earthquake on the north-central BCS occurred before 2 ka, consistent with previous north-central BCS investigations at Bowden Canyon and Box Elder Canyon. At Hansen Canyon, the most recent earthquake is constrained to 2.1–4.2 ka and had 0.6–2.5 m of vertical displacement. At Kotter Canyon, we found evidence for two events at 2.5 ± 0.3 ka and 3.5 ± 0.3 ka, with an average displacement per event of 1.9–2.3 m. Paleoseismic data from Pearsons Canyon, on the previously unstudied southern BCS, indicate that a post-2 ka earthquake ruptured this part of the segment. The Pearsons Canyon earthquake occurred at 1.2 ± 0.04 ka and had 0.1–0.8 m of vertical displacement, consistent with our observation of continuous, youthful scarps on the southern 9 km of the BCS having 1–2 m of late Holocene(?) surface offset. The 1.2-ka earthquake on the southern BCS likely represents rupture across the Weber–Brigham City segment boundary from the penultimate Weber-segment earthquake at about 1.1 ka. The Pearsons Canyon data result in a revised length of the BCS that has not ruptured since 2 ka (with time-dependent probability implications), and provide compelling evidence of at least one segment-boundary failure and multi-segment rupture on the central WFZ. Our

  8. Interplay between magmatic accretion, spreading asymmetry and detachment faulting at a segment end: Crustal structure south of the Ascension Fracture Zone

    NASA Astrophysics Data System (ADS)

    Bialas, Jörg; Dannowski, Anke; Reston, Timothy J.

    2015-12-01

    A wide-angle seismic section across the Mid-Atlantic Ridge just south of the Ascension transform system reveals laterally varying crustal thickness, and to the east a strongly distorted Moho that appears to result from slip along a large-offset normal fault, termed an oceanic detachment fault. Gravity modelling supports the inferred crustal structure. We investigate the interplay between magmatism, detachment faulting and the changing asymmetry of crustal accretion, and consider several possible scenarios. The one that appears most likely is remarkably simple: an episode of detachment faulting which accommodates all plate divergence and results in the westward migration of the ridge axis, is interspersed with dominantly magmatic and moderately asymmetric (most on the western side) spreading which moves the spreading axis back towards the east. Following the runaway weakening of a normal fault and its development into an oceanic detachment fault, magma both intrudes the footwall to the fault, producing a layer of gabbro (subsequently partially exhumed).

  9. Late Cenozoic strike-slip faulting in the NE Mojave Block: Deformation at the southwest boundary of the Walker Lane belt

    SciTech Connect

    Schermer, E.R. . Geology Dept.)

    1993-04-01

    New structural and stratigraphy data from the NE Mojave Block (NEMB) establish the timing and style of Cenozoic deformation south of the Garlock fault and west of the Avawatz Mts. Unlike adjacent areas, most of the NEMB did not undergo early-mid Miocene extension. Major fault zones strike EW; offset markers and small-scale shear criteria indicate left-lateral strike slip with a small reverse component. Lateral offsets average ca. 1--6 km and vertical offset is locally >200m. Pre-Tertiary markers indicate minimum cumulative sinistral shear of ca. 15 km in the area between the Garlock and Coyote Lake faults. Tertiary strata are deformed together with the older rocks. Along the Ft. Irwin fault, alluvial fan deposits interpreted to be <11Ma appear to be displaced as much as Mesozoic igneous rocks. EW sinistral faults S. of the Garlock fault cut unconsolidated Quaternary deposits; geomorphologic features and trench exposures along segments of the McLean Lake fault and the Tiefort Mt. fault suggest Late Quaternary activity. The EW faults do not cut modern drainages and are not seismically active. NW-striking faults are largely absent within the NEMB; the largest faults bound the domain of EW-striking faults. Offset of Cretaceous and Miocene rocks suggests the W boundary (Goldstone Lake fault) has <2km right separation. Along the E boundary (Soda-Avawatz fault zone), the presence of distinctive clasts in mid-late Miocene conglomerates west of the Avawatz Mts. supports the suggestion of Brady (1984) of ca. 20 km dextral displacement. Other NW-striking faults are cut by EW faults, have unknown or minor dextral displacement (Desert King Spring Fault, Garlic Spring fault) or are low- to moderate-angle left-oblique thrust faults (Red Pass Lake fault zone).

  10. Tectonic controls on fault-zone permeability in a geothermal reservoir at Dixie Valley, Nevada

    USGS Publications Warehouse

    Hickman, Stephen; Zoback, Mark; Benoit, Richard

    1998-01-01

    To determine factors controlling permeability variations within and adjacent to a fault-hosted geothermal reservoir at Dixie Valley, Nevada, we conducted borehole televiewer observations of wellbore failure (breakouts and cooling cracks) together with hydraulic fracturing stress measurements in six wells drilled into the Stillwater fault zone at depths of 2 to 3 km. Measurements in highly permeable wells penetrating the main geothermal reservoir indicate that the local orientation of the least horizontal principal stress, Shmin, is nearly optimal for normal faulting on the Stillwater fault. Hydraulic fracturing tests from these wells further show that the magnitude of Shmin is low enough to lead to frictional failure on the Stillwater and nearby subparallel faults, suggesting that fault slip is responsible for the high reservoir productivity. Similar measurements were conducted in two wells penetrating a relatively impermeable segment of the Stillwater fault zone, located approx. 8 and 20 km southwest of the geothermal reservoir (wells 66-21 and 45-14, respectively). The orientation of Shmin in well 66-21 is near optimal for normal faulting on the nearby Stillwater fault, but the magnitude of Shmin is too high to result in incipient frictional failure. In contrast, although the magnitude of Shmin in well 45-14 is low enough to lead to normal faulting on optimally oriented faults, the orientation of the Stillwater fault near this well is rotated by approx. 40?? from the optimal orientation for normal faulting. This misorientation, coupled with an apparent increase in the magnitude of the greatest horizontal principal stress in going from the producing to nonproducing wells, acts to inhibit frictional failure on the Stillwater fault zone in proximity to well 45-14. Taken together, data from the nonproducing and producing wells thus suggest that a necessary condition for high reservoir permeability is that the Stillwater fault zone be critically stressed for

  11. Focal Mechanism Characterization of Microseismicity Near the Alpine Fault, Southern Alps, New Zealand

    NASA Astrophysics Data System (ADS)

    Rawles, C.; Thurber, C. H.; Roecker, S. W.; Feenstra, J. P.; Townend, J.; Bannister, S. C.

    2013-12-01

    Focal mechanisms are determined for earthquakes in the vicinity of the Alpine Fault in the South Island of New Zealand using the P-wave first motion method of Hardebeck and Shearer [2002] and the probabilistic (Bayesian) algorithm of Walsh et al. [2009]. Our results are obtained using data collected from about 40 temporary and permanent stations deployed in a region spanning over a 100 km along-strike portion of the Alpine Fault, roughly centered on the Deep Faulting Drilling Project DFDP-2 drill site near Whataroa. Focal mechanisms and the distribution of seismic activity enable us to address key hypotheses pertaining to the geometry and kinematics of the central Alpine Fault including: 1) the Alpine Fault dip remains close to 50° to the base of the seismogenic zone; 2) the complex surface fault trace, with alternating strike-slip and thrust segments, does not reflect a simpler oblique fault geometry at depth; and 3) the depth to the base of the seismogenic zone is shallower (<15 km) in the Whataroa region than to the northeast. Our focal mechanism results will also provide valuable inputs to stress inversion calculations to be used in determining the principal stress orientations adjacent to the Alpine Fault, which has important ramifications regarding the strength of the Alpine Fault. Such information has obvious implications for understanding the current mechanical state of the Alpine Fault and thereby further characterizing the hazard posed by future large earthquakes.

  12. Geodynamic significance of the TRM segment in the East African Rift: active tectonics and paleostress in western Tanzania

    NASA Astrophysics Data System (ADS)

    Delvaux, D.; Kervyn, F.; Macheyeki, A. S.; Temu, E. B.

    2012-04-01

    The Tanganyika-Rukwa-Malawi (TRM) rift segment in western Tanzania is a key sector for understanding the opening dynamics of the East African rift system (EARS). In an oblique opening model, it is considered as a dextral transfer fault zone that accommodates the general opening of the EARS in a NW-SE direction. In an orthogonal opening model, it accommodates pure dip-slip normal faulting with extension orthogonal to the rift segments and a general E-W extension for the entire EARS. We investigated the active tectonic architecture and paleostress evolution of the Ufipa plateau and adjacent Rukwa basin and in order to define their geodynamic role in the development of the EARS and highlight their pre-rift brittle tectonic history. The active fault architecture, fault-kinematic analysis and paleostress reconstruction show that the recent to active fault systems that control the rift structure develop in a pure extensional setting with extension direction orthogonal to the trend of the TRM segment. Two pre-rift brittle events are evidenced. An older brittle thrusting is related to the interaction between the Bangweulu block and the Tanzanian craton during the late Pan-African (early Paleozoic). It was followed by a transpressional inversion during the early Mesozoic. This inversion stage caused dextral strike-slip faulting along the fault systems that now control the major rift structures. It has been erroneously interpreted as related to the late Cenozoic EARS which instead is characterized by pure normal faulting.

  13. PROPAGATION AND LINKAGE OF OCEANIC RIDGE SEGMENTS.

    USGS Publications Warehouse

    Pollard, David D.; Aydin, Atilla

    1984-01-01

    An investigation was made of spreading ridges and the development of structures that link ridge segments using an analogy between ridges and cracks in elastic plates. The ridge-propagation force and a path factor that controls propagation direction were calculated for echelon ridge segments propagating toward each other. The ridge-propagation force increases as ridge ends approach but then declines sharply as the ends pass, so ridge segments may overlap somewhat. The sign of the path factor changes as ridge ends approach and pass, so the overlapping ridge ends may diverge and then converge following a hook-shaped path. The magnitudes of shear stresses in the plane of the plate and orientations of maximum shear planes between adjacent ridge segments were calculated to study transform faulting. For different loading conditions simulating ridge push, plate pull, and ridge suction, a zone of intense mechanical interaction between adjacent ridge ends in which stresses are concentrated was identified. The magnitudes of mean stresses in the plane of the plate and orientations of principal stress planes were also calculated.

  14. Aftershock source properties of events following the 2013 Craig Earthquake: new evidence for structural heterogeneity on the northern Queen Charlotte Fault

    NASA Astrophysics Data System (ADS)

    Roland, E. C.; Walton, M. A. L.; Ruppert, N. A.; Gulick, S. P. S.; Christeson, G. L.; Haeussler, P. J.

    2014-12-01

    In January 2013, a Mw 7.5 earthquake ruptured a segment of the Queen Charlotte Fault offshore the town of Craig in southeast Alaska. The region of the fault that slipped during the Craig earthquake is adjacent to and possibly overlapping with the northern extent of the 1949 M 8.1 Queen Charlotte earthquake rupture (Canada's largest recorded earthquake), and is just south of the rupture area of the 1972 M 7.6 earthquake near Sitka, Alaska. Here we present aftershock locations and focal mechanisms for events that occurred four months following the mainshock using data recorded on an Ocean Bottom Seismometer (OBS) array that was deployed offshore of Prince of Wales Island. This array consisted of 9 short period instruments surrounding the fault segment, and recorded hundreds of aftershocks during the months of April and May, 2013. In addition to highlighting the primary mainshock rupture plane, aftershocks also appear to be occurring along secondary fault structures adjacent to the main fault trace, illuminating complicated structure, particularly toward the northern extent of the Craig rupture. Focal mechanisms for the larger events recorded during the OBS deployment show both near-vertical strike slip motion consistent with the mainshock mechanism, as well as events with varying strike and a component of normal faulting. Although fault structure along this northern segment of the QCF appears to be considerably simpler than to the south, where a higher degree of oblique convergence leads to sub-parallel compressional deformation structures, secondary faulting structures apparent in legacy seismic reflection data near the Craig rupture may be consistent with the observed seismicity patterns. In combination, these data may help to characterize structural heterogeneity along the northern segment of the Queen Charlotte Fault that contributes to rupture segmentation during large strike slip events.

  15. Trishear for curved faults

    NASA Astrophysics Data System (ADS)

    Brandenburg, J. P.

    2013-08-01

    Fault-propagation folds form an important trapping element in both onshore and offshore fold-thrust belts, and as such benefit from reliable interpretation. Building an accurate geologic interpretation of such structures requires palinspastic restorations, which are made more challenging by the interplay between folding and faulting. Trishear (Erslev, 1991; Allmendinger, 1998) is a useful tool to unravel this relationship kinematically, but is limited by a restriction to planar fault geometries, or at least planar fault segments. Here, new methods are presented for trishear along continuously curved reverse faults defining a flat-ramp transition. In these methods, rotation of the hanging wall above a curved fault is coupled to translation along a horizontal detachment. Including hanging wall rotation allows for investigation of structures with progressive backlimb rotation. Application of the new algorithms are shown for two fault-propagation fold structures: the Turner Valley Anticline in Southwestern Alberta, and the Alpha Structure in the Niger Delta.

  16. Identifying buried segments of active faults in the northern Rio Grande Rift using aeromagnetic, LiDAR,and gravity data, south-central Colorado, USA

    USGS Publications Warehouse

    Ruleman, Cal; Grauch, V. J.

    2013-01-01

    Combined interpretation of aeromagnetic and LiDAR data builds on the strength of the aeromagnetic method to locate normal faults with significant offset under cover and the strength of LiDAR interpretation to identify the age and sense of motion of faults. Each data set helps resolve ambiguities in interpreting the other. In addition, gravity data can be used to infer the sense of motion for totally buried faults inferred solely from aeromagnetic data. Combined interpretation to identify active faults at the northern end of the San Luis Basin of the northern Rio Grande rift has confirmed general aspects of previous geologic mapping but has also provided significant improvements. The interpretation revises and extends mapped fault traces, confirms tectonic versus fluvial origins of steep stream banks, and gains additional information on the nature of active and potentially active partially and totally buried faults. Detailed morphology of surfaces mapped from the LiDAR data helps constrain ages of the faults that displace the deposits. The aeromagnetic data provide additional information about their extents in between discontinuous scarps and suggest that several totally buried, potentially active faults are present on both sides of the valley.

  17. Rupture History of the 1944 Bolu-Gerede Segment of the North Anatolian Fault: Gerede-Ardicli Trench Re-excavated

    NASA Astrophysics Data System (ADS)

    Okumura, K.; Awata, Y.; Duman, T. Y.; Tokay, F.; Kuscu, I.; Kondo, H.

    2002-12-01

    Though the intensive research on the North Anatolian fault after the 1999 Kocaeli earthquake brought a lot of information on the present and past activity of the fault, our knowledge about the rupture history and the past slips along the entire length of the North Anatolian fault is still very limited. More precise data on the timing and amount of past slips along the fault is indispensable to understand the fault behavior in the past and in the future. The Aridicli trench site, 15 km east of Gerede, is one of the most promising sites for this investigation, for abundant datable material and for ideal sedimentation history to record recent earthquakes. Okumura et al. (1990, 1993) opened a trench here in 1990 and concluded 8 earthquake events in 2000 years. However, the conclusion depended mostly on indirect evidence of coseismic deformation along the fault because few master fault strands repeatedly ruptured in pure strike-slip condition and dating was not enough. The Gerede 2002 trench was opened about 18 m east of the 1990 trench, cutting into a 10 m by 10 m light-toned area on an aerial photography. The light-toned area turned out to be a small pressure ridge or dome associated with an a-few-meter-wide restraining jog of the fault. The north side of the fault in the 3-metere-deep trench consists of an anticline of ca. 1000 B.P. to 2000 B.P. lacustrine deposits underlain by 1000 B.P. and younger flood and marsh deposits. Two distinct levels of overlap indicate the timing of events that accompanied the growth of the anticline. The south side of the faults consists of 0 to ca. 1000 B.P. flood and marsh deposits. A basement of a brick kiln is cutting into the deposits and tilted conformably with the dip of the sedimentary units. Steeply north dipping oblique-reverse faults bifurcates from vertical master fault zone. There are three discrete levels of upper terminations of these subsidiary faults, beside the flower structure at the top of the master fault. These four

  18. Tectonic origin for polygonal normal faults in pelagic limestones of the Cingoli anticline hinge (Italy)

    NASA Astrophysics Data System (ADS)

    Petracchini, Lorenzo; Antonellini, Marco; Billi, Andrea; Scrocca, Davide

    2016-04-01

    Polygonal faults are a relatively-recent new class of normal faults which are thought to be formed during early burial and diagenesis as a consequence of heterogeneous lateral volume changes. Polygonal faults are non-systematically oriented and, in map view, they form rhombus-, pentagon-, or hexagon-like pattern, suggesting a non-tectonic origin. Furthermore, polygonal faults are layer bound and they are restricted to particular stratigraphic level. Predicting the pattern of polygonal normal fault results crucial for geofluid exploration and exploitation, but, despite the large number of studies, the origin of these faults remains still largely controversial. One of the main reason for this uncertainty is that they are poorly known in outcrops. Polygonal faults have been identified in few localities within Mesozoic chalk (United Kingdom, France, and Egypt), in Paleogene claystone (Belgium), and in the Cretaceous Khoman Formation (Egypt) where polygonal faults have been observed in an extensive exposure of chalk. In this study, we describe an outcrop in the Cingoli anticline hinge, which is located at external front of the northern Apennines fold-thrust belt (Italy), showing normal faults that we interpreted as syn-tectonically (syn-thrusting) polygonal faults. The outcrop shows three vertical exposures of sub-horizontal fine-grained marly limestones with chert interlayers of Albian-Turonian age. Intraformational short normal faults affect the carbonate and chert beds. These faults are poorly-systematic and they cut through the carbonate beds whereas usually stop against the chert layers. The fault surfaces are often characterized by slickolites, clayey residue, and micro-breccias including clasts of chert and carbonate. Fault displacement is partly or largely accommodated by pressure solution. At the fault tips, the displacement is generally transferred, via a lateral step, to an adjacent similar fault segment. The aim of our study is to understand the nucleation

  19. Stress interaction between subduction earthquakes and forearc strike-slip faults: Modeling and application to the northern Caribbean plate boundary

    USGS Publications Warehouse

    ten Brink, U.; Lin, J.

    2004-01-01

    Strike-slip faults in the forearc region of a subduction zone often present significant seismic hazard because of their proximity to population centers. We explore the interaction between thrust events on the subduction interface and strike-slip faults within the forearc region using three-dimensional models of static Coulomb stress change. Model results reveal that subduction earthquakes with slip vectors subparallel to the trench axis enhance the Coulomb stress on strike-slip faults adjacent to the trench but reduce the stress on faults farther back in the forearc region. In contrast, subduction events with slip vectors perpendicular to the trench axis enhance the Coulomb stress on strike-slip faults farther back in the forearc, while reducing the stress adjacent to the trench. A significant contribution to Coulomb stress increase on strike-slip faults in the back region of the forearc comes from "unclamping" of the fault, i.e., reduction in normal stress due to thrust motion on the subduction interface. We argue that although Coulomb stress changes from individual subduction earthquakes are ephemeral, their cumulative effects on the pattern of lithosphere deformation in the forearc region are significant. We use the Coulomb stress models to explain the contrasting deformation pattern between two adjacent segments of the Caribbean subduction zone. Subduction earthquakes with slip vectors nearly perpendicular to the Caribbean trench axis is dominant in the Hispaniola segment, where the strike-slip faults are more than 60 km inland from the trench. In contrast, subduction slip motion is nearly parallel to the Caribbean trench axis along the Puerto Rico segment, where the strike-slip fault is less than 15 km from the trench. This observed jump from a strike-slip fault close to the trench axis in the Puerto Rico segment to the inland faults in Hispaniola is explained by different distributions of Coulomb stress in the forearc region of the two segments, as a result

  20. Seismic imaging of deformation zones associated with normal fault-related folding

    NASA Astrophysics Data System (ADS)

    Lapadat, Alexandru; Imber, Jonathan; Iacopini, David; Hobbs, Richard

    2016-04-01

    Folds associated with normal faulting, which are mainly the result of fault propagation and linkage of normal fault segments, can exhibit complex deformation patterns, with multiple synthetic splay faults, reverse faults and small antithetic Riedel structures accommodating flexure of the beds. Their identification is critical in evaluating connectivity of potential hydrocarbon reservoirs and sealing capacity of faults. Previous research showed that seismic attributes can be successfully used to image complex structures and deformation distribution in submarine thrust folds. We use seismic trace and coherency attributes, a combination of instantaneous phase, tensor discontinuity and semblance attributes to identify deformation structures at the limit of seismic resolution, which accommodate seismic scale folding associated with normal faulting from Inner Moray Firth Basin, offshore Scotland. We identify synthetic splay faults and reverse faults adjacent to the master normal faults, which are localized in areas with highest fold amplitudes. This zone of small scale faulting is the widest in areas with highest fault throw / fold amplitude, or where a bend is present in the main fault surface. We also explore the possibility that changes in elastic properties of the rocks due to deformation can contribute to amplitude reductions in the fault damage zones. We analyse a pre-stack time-migrated 3D seismic data-set, where seismic reflections corresponding to a regionally-continuous and homogeneous carbonate layer display a positive correlation between strain distribution and amplitude variations adjacent to the faults. Seismic amplitude values are homogeneously distributed within the undeformed area of the footwall, with a minimum deviation from a mean amplitude value calculated for each seismic line. Meanwhile, the amplitude dimming zone is more pronounced (negative deviation increases) and widens within the relay zone, where sub-seismic scale faults, which accommodate

  1. Laramide structure of the central Sangre de Cristo Mountains and adjacent Raton Basin, southern Colorado

    USGS Publications Warehouse

    Lindsey, D.A.

    1998-01-01

    Laramide structure of the central Sangre de Cristo Mountains (Culebra Range) is interpreted as a system of west-dipping, basement-involved thrusts and reverse faults. The Culebra thrust is the dominant structure in the central part of the range; it dips 30 -55?? west and brings Precambrian metamorphic base-ment rocks over unmetamorphosed Paleozoic rocks. East of the Culebra thrust, thrusts and reverse faults break the basement and overlying cover rocks into north-trending fault blocks; these boundary faults probably dip 40-60?? westward. The orientation of fault slickensides indicates oblique (northeast) slip on the Culebra thrust and dip-slip (ranging from eastward to northward) movement on adjacent faults. In sedimentary cover rocks, east-vergent anticlines overlie and merge with thrusts and reverse faults; these anticlines are interpreted as fault-propagation folds. Minor east-dipping thrusts and reverse faults (backthrusts) occur in both the hanging walls and footwalls of thrusts. The easternmost faults and folds of the Culebra Range form a continuous structural boundary between the Laramide Sangre de Cristo highland and the Raton Basin. Boundary structures consist of west-dipping frontal thrusts flanked on the basinward side by poorly exposed, east-dipping backthrusts. The backthrusts are interpreted to overlie structural wedges that have been emplaced above blind thrusts in the basin margin. West-dipping frontal thrusts and blind thrusts are interpreted to involve basement, but backthrusts are rooted in basin-margin cover rocks. At shallow structural levels where erosion has not exposed a frontal thrust, the structural boundary of the basin is represented by an anticline or monocline. Based on both regional and local stratigraphic evidence, Laramide deformation in the Culebra Range and accompanying synorogenic sedimentation in the western Raton Basin probably took place from latest Cretaceous through early Eocene time. The earliest evidence of uplift and

  2. Variation in aseismic slip and fault normal strain along the creeping section of the San Andreas fault from GPS, InSAR and trilateration data

    NASA Astrophysics Data System (ADS)

    Rolandone, F.; Johanson, I.; Bürgmann, R.; Agnew, D.

    2004-12-01

    In central California most of the relative motion between the Pacific and North American plates is accommodated by strike slip along the San Andreas fault system. However, a small amount of convergence is accommodated by compressional structures in the California Coast Ranges on both sides of the fault. Recent examples of such activity are the Coalinga and the 2003 San Simeon earthquakes. Along the central San Andreas fault (CSAF), from San Juan Bautista to Parkfield, almost all the slip along the CSAF in the brittle upper crust is accommodated aseismically. We use GPS, InSAR and trilateration data to resolve both the distribution of aseismic slip along the CSAF, and the deformation across adjacent, secondary fault structures. In 2003 and 2004, we conducted several GPS surveys along the CSAF. We resurveyed 15 stations of the San Benito triangulation and trilateration network, which extends 40 km to the northeast of the creeping segment. We combine these measurements with old EDM measurements and data from a GPS campaign in 1998. We also occupied 13 sites along the creeping segment, for which previous data exist in the SCEC archive. These dense GPS measurements, along with data from permanent GPS stations in the area, allow us to constrain the regional strain distribution and contributions from adjacent faults. With the addition of InSAR data, we can also better resolve active strain accumulation and aseismic slip along the CSAF. We use a stack of about 10 interferograms from ERS-1 and ERS-2 satellites spanning 8 years. InSAR is well suited to monitoring details of the shallow slip along the CSAF and, in concert with the broadly spaced GPS velocities, to resolving the distribution of deformation along and across the plate boundary. The results are the basis for determining the kinematics of spatially variable fault slip on the CSAF, and help to better constrain the fault's constitutive properties, and fault interaction processes.

  3. Three-dimensional seismic structure of a Mid-Atlantic Ridge segment characterized by active detachment faulting (TAG, 25°55’N-26°20’N)

    NASA Astrophysics Data System (ADS)

    Zhao, M.; Canales, J.

    2009-12-01

    The Trans-Atlantic Geotraverse (TAG) segment of the Mid-Atlantic Ridge (MAR) (25°55'N-26°20'N) is characterized by massive active and relict high-temperature hydrothermal deposits. Previous geological and geophysical studies indicate that the active TAG hydrothermal mound sits on the hanging wall of an active detachment fault. The STAG microseismicity study revealed that seismicity associated to detachment faulting extends deep into the crust/uppermost mantle (>6 km), forming an arcuate band (in plan view) extending along ~25 km of the rift valley floor (deMartin et al., Geology, 35, 711-714, 2007). Two-dimensional analysis of the STAG seismic refraction data acquired with ocean bottom seismometers (OBSs) showed that the eastern rift valley wall is associated with high P-wave velocities (>7 km/s) at shallow levels (>1 km depth), indicating uplift of lower crustal and/or upper mantle rocks along the detachment fault (Canales et al., Geochem., Geophys., Geosyst., 8, Q08004, doi:08010.01029/02007GC001629, 2008). Here we present a three-dimensional (3D) seismic tomography analysis of the complete STAG seismic refraction OBS dataset to illuminate the 3D crustal architecture of the TAG segment. Our new results provide, for the first time, a detailed picture of the complex, dome-shaped geometry and structure of a nascent oceanic core complex being exhumed by a detachment fault. Our results show a relatively low-velocity anomaly embedded within the high-velocity body forming the footwall of the detachment fault. The low velocity sits 2-3 km immediately beneath the active TAG hydrothermal mound. Although velocities within the low-velocity zone are too high (6 km/s) to represent partial melt, we speculate that this low velocity zone is intimately linked to hydrothermal processes taking place at TAG. We consider three possible scenarios for its origin: (1) a highly fissured zone produced by extensional stresses during footwall exhumation that may help localize fluid flow

  4. Cell boundary fault detection system

    DOEpatents

    Archer, Charles Jens; Pinnow, Kurt Walter; Ratterman, Joseph D.; Smith, Brian Edward

    2009-05-05

    A method determines a nodal fault along the boundary, or face, of a computing cell. Nodes on adjacent cell boundaries communicate with each other, and the communications are analyzed to determine if a node or connection is faulty.

  5. A Fault-based Crustal Deformation Model for UCERF3 and Its Implication to Seismic Hazard Analysis

    NASA Astrophysics Data System (ADS)

    Zeng, Y.; Shen, Z.

    2012-12-01

    We invert GPS data to determine slip rates on major California faults using a fault-based crustal deformation model with geological slip rate constraints. The model assumes buried elastic dislocations across the region using fault geometries defined by the Uniform California Earthquake Rupture Forecast version 3 (UCERF3) project with fault segments slipping beneath their locking depths. GPS observations across California and neighboring states were obtained from the UNAVCO western US GPS velocity model and edited by the SCEC UCERF3 geodetic deformation working group. The geologic slip rates and fault style constraints were compiled by the SCEC UCERF3 geologic deformation working group. Continuity constraints are imposed on slips among adjacent fault segments to regulate slip variability and to simulate block-like motion. Our least-squares inversion shows that slip rates along the northern San Andreas fault system agree well with the geologic estimates provided by UCERF3, and slip rates for the Calaveras-Hayward-Maacama fault branch and the Greenville-Great Valley fault branch are slightly higher than that of the UCERF3 geologic model. The total slip rates across transects of the three fault branches in Northern California amount to 39 mm/yr. Slip rates determined for the Garlock fault closely match geologic rates. Slip rates for the Coachella Valley and Brawley segment of the San Andreas are nearly twice that of the San Jacinto fault branch. For the off-coast faults along the San Gregorio, Hosgri, Catalina, and San Clemente faults, slip rates are near their geologic lower bounds. Comparing with the regional geologic slip rate estimates, the GPS based model shows a significant decrease of 6-14 mm/yr in slip rates along the San Andreas fault system from the central California creeping section through the Mojave to the San Bernardino Mountain segments, whereas the model indicates significant increase of 1-3 mm/yr in slip-rates for faults along the east California

  6. Structures associated with strike-slip faults that bound landslide elements

    USGS Publications Warehouse

    Fleming, R.W.; Johnson, A.M.

    1989-01-01

    Large landslides are bounded on their flanks and on elements within the landslides by structures analogous to strike-slip faults. We observed the formation of thwse strike-slip faults and associated structures at two large landslides in central Utah during 1983-1985. The strike-slip faults in landslides are nearly vertical but locally may dip a few degrees toward or away from the moving ground. Fault surfaces are slickensided, and striations are subparallel to the ground surface. Displacement along strike-slip faults commonly produces scarps; scarps occur where local relief of the failure surface or ground surface is displaced and becomes adjacent to higher or lower ground, or where the landslide is thickening or thinning as a result of internal deformation. Several types of structures are formed at the ground surface as a strike-slip fault, which is fully developed at some depth below the ground surface, propagates upward in response to displacement. The simplest structure is a tension crack oriented at 45?? clockwise or counterclockwise from the trend of an underlying right- or left-lateral strike-slip fault, respectively. The tension cracks are typically arranged en echelon with the row of cracks parallel to the trace of the underlying strike-slip fault. Another common structure that forms above a developing strike-slip fault is a fault segment. Fault segments are discontinuous strike-slip faults that contain the same sense of slip but are turned clockwise or counterclockwise from a few to perhaps 20?? from the underlying strike-slip fault. The fault segments are slickensided and striated a few centimeters below the ground surface; continued displacement of the landslide causes the fault segments to open and a short tension crack propagates out of one or both ends of the fault segments. These structures, open fault segments containing a short tension crack, are termed compound cracks; and the short tension crack that propagates from the tip of the fault segment

  7. Fault terminations, Seminoe Mountains, Wyoming

    SciTech Connect

    Dominic, J.B.; McConnell, D.A. . Dept. of Geology)

    1992-01-01

    Two basement-involved faults terminate in folds in the Seminoe Mountains. Mesoscopic and macroscopic structures in sedimentary rocks provide clues to the interrelationship of faults and folds in this region, and on the linkage between faulting and folding in general. The Hurt Creek fault trends 320[degree] and has maximum separation of 1.5 km measured at the basement/cover contact. Separation on the fault decreases upsection to zero within the Jurassic Sundance Formation. Unfaulted rock units form an anticline around the fault tip. The complementary syncline is angular with planar limbs and a narrow hinge zone. The syncline axial trace intersects the fault in the footwall at the basement/cover cut-off. Map patterns are interpreted to show thickening of Mesozoic units adjacent to the syncline hinge. In contrast, extensional structures are common in the faulted anticline within the Permian Goose Egg and Triassic Chugwater Formations. A hanging wall splay fault loses separation into the Goose Egg formation which is thinned by 50% at the fault tip. Mesoscopic normal faults are oriented 320--340[degree] and have an average inclination of 75[degree] SW. Megaboudins of Chugwater are present in the footwall of the Hurt Creek fault, immediately adjacent to the fault trace. The Black Canyon fault transported Precambrian-Pennsylvanian rocks over Pennsylvanian Tensleep sandstone. This fault is layer-parallel at the top of the Tensleep and loses separation along strike into an unfaulted syncline in the Goose Egg Formation. Shortening in the pre-Permian units is accommodated by slip on the basement-involved Black Canyon fault. Equivalent shortening in Permian-Cretaceous units occurs on a system of thin-skinned'' thrust faults.

  8. Petrography of volcaniclastic rocks in intra-arc volcano-bounded to fault-bounded basins of the Rosario segment of the Lower Cretaceous Alisitos oceanic arc, Baja California, Mexico

    NASA Astrophysics Data System (ADS)

    Marsaglia, K. M.; Barone, M.; Critelli, S.; Busby, C.; Fackler-Adams, B.

    2016-05-01

    The Rosario segment of the Early Cretaceous Alisitos oceanic magmatic arc in Baja California displays a record of arc-axis sedimentation and volcanism that is well preserved in outcrops within a southern volcano-bounded and a northern fault-bounded basin that flanked an intervening subaerial edifice. This record includes volcanic and volcaniclastic rocks that range from felsic to mafic in composition. Volcaniclastic/tuffaceous sandstone samples from two previously published measured sections are mainly composed of volcanic clasts with moderate plagioclase content. Locally quartz and/or potassium feldspar are present in trace to moderate amounts. The proportions of volcanic lithic types exhibiting vitric, microlitic, lathwork, and felsitic textures are highly variable with no distinct stratigraphic trends, likely as a function of the mixed styles of eruption and magma compositions that produced pyroclasts, as well as erosion-produced epiclastic debris. The volcaniclastic fill of the basins is consistent with an oceanic arc setting, except for the relatively high felsitic volcanic lithic content, likely associated with subaerial, as opposed to the more common submarine felsic magmatism associated with arc extension in oceanic settings. There are no major differences in compositional modes of tuff and sandstone between the fault-bounded and volcano-bounded basin strata, even though they exhibit distinctly different volcaniclastic facies. This suggests that proximal arc-axis basins of varying types around a single major subaerial edifice provide a faithful record of volcanic trends in the arc segment, regardless of variation in transport and depositional processes.

  9. Seismic Reflection Project Near the Southern Terminations of the Lost River and Lemhi Faults, Eastern Snake River Plain, Idaho

    SciTech Connect

    S. M. Jackson; G. S. Carpenter; R. P. Smith; J. L. Casper

    2006-10-01

    Thirteen seismic reflection lines were processed and interpreted to determine the southern terminations of the Lost River and Lemhi faults along the northwest boundary of the eastern Snake River Plain (ESRP). The southernmost terminations of the Arco and Howe segments were determined to support characterization of the Lost River and Lemhi fault sources, respectively, for the INL probabilistic seismic hazard analysis. Keywords:Keywords are required forExternal Release Review*Keywords  Keywords *Contacts (Type and Name are required for each row) Type ofContactContact Name  POC Editor RecordFour commercial seismic reflection lines (Arco lines 81-1 and 81-2; Howe lines 81-3 and 82-2) were obtained from the Montana Power Company. The seismic data were collected in the early 1980’s using a Vibroseis source with station and shot point locations that resulted in 12-fold data. Arco lines 81?1 and 81?2 and Howe lines 81?3 and 82?2 are located within the basins adjacent to the Arco and Howe segments, respectively. Seven seismic lines (Arco lines A1, A2, A3, and A4 and Howe lines H1, H2, and H3) were acquired by EG&G Idaho, Inc. Geosciences for this study using multiple impacts with an accelerated weight drop source. Station and shot point locations yielded 12-fold data. The seismic reflection lines are oriented perpendicular to and at locations along the projected extensions of the Arco and Howe fault segments within the ESRP. Two seismic lines (Arco line S2 and Howe line S4) were obtained from Sierra Geophysics. In 1984, they acquired seismic reflection data using an accelerated weight drop source with station and shot point locations that yielded 6-fold data. The two seismic reflection lines are oriented perpendicular to and at locations along the projected extensions of the Arco and Howe fault segments within the ESRP. In 1992 for this study, Geotrace Technologies Inc. processed all of the seismic reflection data using industry standard processing techniques. The

  10. Gas migration pathways in a complex faulted hangingwall in the western part of the Norwegian Danish Basin

    NASA Astrophysics Data System (ADS)

    Mauritzen, Emil K.; Clausen, Ole R.; Andresen, Katrine J.

    2013-04-01

    The studied fault is positioned in the westernmost Danish part of the Norwegian Danish Basin at the southern margin of the Northern Permian Basin. The dominating fault is the so called D-1 fault, which is part of a fault trend which follows the southern pinch-out line of the Zechstein salt and detach along the top Zechstein evaporites. Just north of the D-1 fault is the only Danish commercial HC producing area outside the Mesozoic Central Graben -the Siri Canyon- located The presence of gas within the Neogene sediments at the hanging-wall of the D-1 fault was reported in the D-1 well and the D-1 fault was analyzed in detail using 2-D seismic data in the early 90-ies. Due to the open seismic grid used then it was not possible to link the presence of possible gas occurrences and the faults as well as linking the small faults associated to the hanging-wall deformation. The area was subject to renewed interest due to the HC discoveries in the Siri Valley and industrial 3-D seismic data was acquired covering the D-1 fault.The 3D seismic data has enabled a very detailed mapping of the entire D-1 fault complex as well as seismic attribute analysis (courtesy OpendTect). The D-1 fault is in map-view characterized by segments approximately 10 km long striking E-W and NE-SW respectively. In the Cretaceous and Cenozoic part is the main fault coherent whereas the antithetic and secondary synthetic faults in the hanging-wall are smaller (both with respect to offset and length). The character of the internal hanging-wall faults varies along strike of the main fault. In areas adjacent to NE-SW striking segments is the number of faults much higher and they strike both parallel to the main fault and at an angle to it; whereas the faults are longer, less numerous and dominantly parallel to the main fault in the E-W striking central parts. Gas occurrences are observed as bright-spots associated to small faults in the hanging-wall next to the NE-SW striking segments, whereas

  11. Early Jurassic rift structures associated with the Soapaga and Boyacá faults of the Eastern Cordillera, Colombia: Sedimentological inferences and regional implications

    NASA Astrophysics Data System (ADS)

    Kammer, Andreas; Sánchez, Javier

    2006-09-01

    The NW-trending Bucaramanga fault links, at its southern termination, with the Soapaga and Boyacá faults, which by their NW trend define an ample horsetail structure. As a result of their Neogene reactivation as reverse faults, they bound fault-related anticlines that expose the sedimentary fill of two Early Jurassic rift basins. These sediments exhibit the wedge-like geometry of rift fills related to west-facing normal faults. Their structural setting was controlled further by segmentation of the bounding faults at approximately 10 km intervals, in which each segment is separated by a transverse basement high. Isopach contours and different facies associations suggest these transverse anticlines may have separated depocenters of their adjacent subbasins, which were shaped by a slightly different subsidence history and thereby decoupled. The basin fill of the relatively narrow basin associated with the Soapaga fault is dominated by fanglomeratic successions organized in two coarsening-upward cycles. In the larger basin linked to the Boyacá fault, the sedimentary fill consists of two coarsening-upward sequences that, when fully developed, vary from floodplain to alluvial fan deposits. These Early Jurassic rift fills temporally constrain the evolution of the Bucaramanga fault, which accommodated right-lateral displacement during the early Mesozoic rift event.

  12. Applying geophysical techniques to investigate a segment of a creeping fault in the urban area of San Gregorio di Catania, southern flank of Mt. Etna (Sicily - Italy)

    NASA Astrophysics Data System (ADS)

    Imposa, S.; De Guidi, G.; Grassi, S.; Scudero, S.; Barreca, G.; Patti, G.; Boso, D.

    2015-12-01

    In an especially built-up area, such as the lower slopes of Etna volcano, the effects of surface faulting, caused by coseismic ruptures and aseismic creep, contribute significantly to increase the risk to towns and villages and their related infrastructure. This study aims to couple the geophysical and structural characteristics of an active fault zone, joining surficial and deep information, in the area of San Gregorio di Catania (Sicily - Italy). The occurrence of this structure and its associated fracture field were related to variations in the physical and mechanical properties of the hosting rocks. Surface structural survey detected a fracture zone with maximum width of 40 m, characterized with fractures oriented consistently with the kinematics of the fault. The geophysical surveys (ground penetrating radar, seismic tomography, and refraction microtremor), enabled to detect highly fractured rock volumes at variable depth whose occurrence has been linked to the presence of the fault at surface. The integration of various techniques, with different spatial resolution and depth range, allowed to fully reconstruct the 3D geological structure of the site down to about 15 m.

  13. Stress state of the Baoxing segment of the southwestern Longmenshan Fault Zone before and after the Ms 7.0 Lushan earthquake

    NASA Astrophysics Data System (ADS)

    Wu, Manlu; Zhang, Chongyuan; Fan, Taoyuan

    2016-05-01

    In situ stress measurements were conducted with hydraulic fracturing and piezomagnetic overcoring method in a borehole at Qiaoqi of Baoxing region in the southwestern Longmenshan Fault Zone, to understand the current stress state and stress change after the Ms 7.0 Lushan earthquake. The stress regime of the Qiaoqi borehole is characterized by SH > Sh > Sv, indicating that the regional stress field is dominated by the maximum horizontal stress and this stress regime is prone to reverse faulting. Impression tests show that the orientations of the maximum horizontal principal stress are NW-NWW oriented. The magnitudes of the maximum horizontal principal stress at Qiaoqi are obviously higher than those before the Lushan earthquake, signifying that stress is still accumulating in this region. The real-time stress monitoring data shows that the stress in the NWW direction is increasing continuously before and after the earthquake. Authors have computed the frictional parameter, μm, using the derived stress data. The result demonstrates a high stress build-up level in the shallow crust before and after the Lushan earthquake. Adopting the Coulomb frictional-failure criteria, we conclude that Baoxing area, the southwestern section of the Longmenshan Fault Zone has already reached or exceeded a frictional limit equilibrium state. Evidence shows that the Lushan earthquake did not release the highly accumulated stress of the southwestern Longmenshan Fault Zone and the potential risk of earthquakes in this region still exists.

  14. Row fault detection system

    SciTech Connect

    Archer, Charles Jens; Pinnow, Kurt Walter; Ratterman, Joseph D.; Smith, Brian Edward

    2008-10-14

    An apparatus, program product and method checks for nodal faults in a row of nodes by causing each node in the row to concurrently communicate with its adjacent neighbor nodes in the row. The communications are analyzed to determine a presence of a faulty node or connection.

  15. Row fault detection system

    DOEpatents

    Archer, Charles Jens; Pinnow, Kurt Walter; Ratterman, Joseph D.; Smith, Brian Edward

    2010-02-23

    An apparatus and program product check for nodal faults in a row of nodes by causing each node in the row to concurrently communicate with its adjacent neighbor nodes in the row. The communications are analyzed to determine a presence of a faulty node or connection.

  16. Row fault detection system

    DOEpatents

    Archer, Charles Jens; Pinnow, Kurt Walter; Ratterman, Joseph D.; Smith, Brian Edward

    2012-02-07

    An apparatus, program product and method check for nodal faults in a row of nodes by causing each node in the row to concurrently communicate with its adjacent neighbor nodes in the row. The communications are analyzed to determine a presence of a faulty node or connection.

  17. Thermal structure of oceanic transform faults

    USGS Publications Warehouse

    Behn, M.D.; Boettcher, M.S.; Hirth, G.

    2007-01-01

    We use three-dimensional finite element simulations to investigate the temperature structure beneath oceanic transform faults. We show that using a rheology that incorporates brittle weakening of the lithosphere generates a region of enhanced mantle upwelling and elevated temperatures along the transform; the warmest temperatures and thinnest lithosphere are predicted to be near the center of the transform. Previous studies predicted that the mantle beneath oceanic transform faults is anomalously cold relative to adjacent intraplate regions, with the thickest lithosphere located at the center of the transform. These earlier studies used simplified rheologic laws to simulate the behavior of the lithosphere and underlying asthenosphere. We show that the warmer thermal structure predicted by our calculations is directly attributed to the inclusion of a more realistic brittle rheology. This temperature structure is consistent with a wide range of observations from ridge-transform environments, including the depth of seismicity, geochemical anomalies along adjacent ridge segments, and the tendency for long transforms to break into small intratransform spreading centers during changes in plate motion. ?? 2007 Geological Society of America.

  18. Polyscale, polymodal fault geometries: evolution and predictive capability

    NASA Astrophysics Data System (ADS)

    Blenkinsop, T. G.; Carvell, J.; Clarke, G.; Tonelli, M.

    2012-12-01

    The Late Permian Rangal coal measures on the edge of the Nebo synclinorium in the Bowen basin, NE Queensland, Australia, are cut by normal faults. Mining operations allow 13 faults to be mapped in some detail to depths of 200m. These faults cut Tertiary intrusions and a reverse fault as well as the coal seams, and show no obvious signs of reactivation. The steeply dipping faults are clustered into groups of two to four, separated by hundreds of meters. The faults trend ENE and NE; both trends of faults dip in both directions, defining a quadrimodal geometry. The odd axis construction for these faults suggests that vertical shortening was accompanied by horizontal extension along both principal directions of 153° and 063°. The mapped extents of the faults are limited by erosion and the depth to which the faults have been drilled, but displacement profiles along the lengths of the faults show maxima within the fault planes. The displacement profiles suggest that the currently mapped faults have similar lengths to the total preserved lengths of the faults, and that they will continue into the unmined ground to a limited, but predictable extent. The fault planes have a complex geometry, with segments of individual faults showing a similar variability in orientation to the ensemble of fault planes: the fault planes themselves are polymodal. Displacement profiles show a good correlation with segment orientation. An odd axis construction based on fault segments, rather than individual faults, gives principal extension directions within 4° of the above results. The variable orientation of fault segments, the correlation of the displacement profiles with fault orientation, and the similarity between the segment and ensemble fault kinematics suggest that the faults have evolved by propagation and linking of smaller polymodal faults in the same bulk strain field.ross section of polymodal fault at Hail Creek coal mine

  19. Principal fault zone width and permeability of the active Neodani fault, Nobi fault system, Southwest Japan

    NASA Astrophysics Data System (ADS)

    Tsutsumi, A.; Nishino, S.; Mizoguchi, K.; Hirose, T.; Uehara, S.; Sato, K.; Tanikawa, W.; Shimamoto, T.

    2004-02-01

    The internal structure and permeability of the Neodani fault, which was last activated at the time of the 1891 Nobi earthquake (M8.0), were examined through field survey and experiments. A new exposure of the fault at a road construction site reveals a highly localized feature of the past fault deformation within a narrow fault core zone. The fault of the area consists of three zone units towards the fault core: (a) protolith rocks; (b) 15 to 30 m of fault breccia, and (c) 200 mm green to black fault gouge. Within the fault breccia zone, cataclastic foliation oblique to the fault has developed in a fine-grained 2-m-wide zone adjacent to the fault. Foliation is defined by subparallel alignment of intact lozenge shaped clasts, or by elongated aggregates of fine-grained chert fragments. The mean angle of 20°, between the foliation and the fault plane suggests that the foliated breccia accommodated a shear strain of γ<5 assuming simple shear for the rotation of the cataclastic foliation. Previous trench surveys have revealed that the fault has undergone at least 70 m of fault displacement within the last 20,000 years in this locality. The observed fault geometry suggests that past fault displacements have been localized into the 200-mm-wide gouge zone. Gas permeability analysis of the gouges gives low values of the order of 10 -20 m 2. Water permeability as low as 10 -20 m 2 is therefore expected for the fault gouge zone, which is two orders of magnitude lower than the critical permeability suggested for a fault to cause thermal pressurization during a fault slip.

  20. Coulomb stress transfer and tectonic loading preceding the 2002 Denali fault earthquake

    USGS Publications Warehouse

    Bufe, C.G.

    2006-01-01

    Pre-2002 tectonic loading and Coulomb stress transfer are modeled along the rupture zone of the M 7.9 Denali fault earthquake (DFE) and on adjacent segments of the right-lateral Denali-Totschunda fault system in central Alaska, using a three-dimensional boundary-element program. The segments modeled closely follow, for about 95??, the arc of a circle of radius 375 km centered on an inferred asperity near the northeastern end of the intersection of the Patton Bay fault with the Alaskan megathrust under Prince William Sound. The loading model includes slip of 6 mm/yr below 12 km along the fault system, consistent with rotation of the Wrangell block about the asperity at a rate of about 1??/m.y. as well as slip of the Pacific plate at 5 cm/yr at depth along the Fairweather-Queen Charlotte transform fault system and on the Alaska megathrust. The model is consistent with most available pre-2002 Global Positioning System (GPS) displacement rate data. Coulomb stresses induced on the Denali-Totschunda fault system (locked above 12 km) by slip at depth and by transfer from the M 9.2 Prince William Sound earthquake of 1964 dominated the changing Coulomb stress distribution along the fault. The combination of loading (???70-85%) and coseismic stress transfer from the great 1964 earthquake (???15-30%) were the principal post-1900 stress factors building toward strike-slip failure of the northern Denali and Totschunda segments in the M 7.9 earthquake of November 2002. Postseismic stresses transferred from the 1964 earthquake may also have been a significant factor. The M 7.2-7.4 Delta River earthquake of 1912 (Carver et al., 2004) may have delayed or advanced the timing of the DFE, depending on the details and location of its rupture. The initial subevent of the 2002 DFE earthquake was on the 40-km Susitna Glacier thrust fault at the western end of the Denali fault rupture. The Coulomb stress transferred from the 1964 earthquake moved the Susitna Glacier thrust fault uniformly

  1. Structure and kinematics of the Livingstone Mountains border fault zone, Nyasa (Malawi) Rift, southwestern Tanzania

    NASA Astrophysics Data System (ADS)

    Wheeler, Walter H.; Karson, Jeffrey A.

    Reconnaissance mapping of the Livingstone Mountains border fault zone (LMBFZ) at the northern end of the Nyasa (Malawi) Rift in SW Tanzania constrains the geometry and movement history of this typical rift border fault. The fault is a narrow zone of complex brittle deformation, striking 320°, that overprints and reactivates an older ductile shear zone. Long, straight, NW-trending border fault segments are offset by minor NE-trending faults. These two orthogonal fault sets integrate along strike to produce an overall curved fault trace that is concave towards a major depositional basin in the rift. A typical section through the fault zone shows an E to W progression from gneissic country rock through ductilely deformed country rock, into a zone overprinted by closely spaced fractures and grading into an intensely fractured, massive, flinty, aphanitic mylonite band at the lakeshore. Pseudotachylite veins, probably generated during seismic movement on the border fault, are common within and near the aphanitic mylonite. Slickensides indicate dextral oblique-slip, whereas shear belts and rolled porphyroclasts with complex tails in the older ductile shear zone indicate sub-horizontal sinistral motion. The adjacent rift basin is typical of other East African Rift Basins, and contains at least 4 km of Recent to perhaps Mesozoic sediment. Whereas the minimum net slip on the LMBFZ, in the dominant slickenside direction, is on the order of 10 km, regional geologic considerations suggest that dominantly strike-slip motion preceded the oblique-slip phase that produced the LMBFZ and the adjacent rift basin.

  2. The Pingding segment of the Altyn Tagh Fault (91 °E): Holocene slip-rate determination from cosmogenic radionuclide dating of offset fluvial terraces

    DOE PAGES

    Meriaux, A. -S.; Van der Woerd, J.; Tapponnier, P.; Ryerson, F. J.; Finkel, R. C.; Lasserre, C.; Xu, X.

    2012-09-25

    Morphochronologic slip-rates on the Altyn Tagh Fault (ATF) along the southern front of the Pingding Shan at ~90.5°E are determined by cosmogenic radionuclide (CRN) dating of seven offset terraces at two sites. The terraces are defined based upon morphology, elevation and dating, together with fieldwork and high-resolution satellite analysis. The majority of the CRN model ages fall within narrow ranges (<2 ka) on the four main terraces (T1, T2, T3 and T3′), and allow a detailed terrace chronology. Bounds on the terrace ages and offsets of 5 independent terraces yield consistent slip-rate estimates. The long-term slip-rate of 13.9 ± 1.1more » mm/yr is defined at the 95% confidence level, as the joint rate probability distribution of the rate derived from each independent terrace. It falls within the bounds of all the rates defined on the central Altyn Tagh Fault between the Cherchen He (86.4°E) and Akato Tagh (~88°E) sites. This rate is ~10 mm/yr less than the upper rate determined near Tura at ~87°E, in keeping with the inference of an eastward decreasing rate due to progressive loss of slip to thrusts branching off the fault southwards but it is greater than the 9 ± 4 mm/yr rate determined at ~90°E by GPS surveys and other geodetic short-term rates defined elsewhere along the ATF. Furthermore, whether such disparate rates will ultimately be reconciled by a better understanding of fault mechanics, resolved transient deformations during the seismic cycle or by more accurate measurements made with either approach remains an important issue.« less

  3. The Pingding segment of the Altyn Tagh Fault (91 °E): Holocene slip-rate determination from cosmogenic radionuclide dating of offset fluvial terraces

    SciTech Connect

    Meriaux, A. -S.; Van der Woerd, J.; Tapponnier, P.; Ryerson, F. J.; Finkel, R. C.; Lasserre, C.; Xu, X.

    2012-09-25

    Morphochronologic slip-rates on the Altyn Tagh Fault (ATF) along the southern front of the Pingding Shan at ~90.5°E are determined by cosmogenic radionuclide (CRN) dating of seven offset terraces at two sites. The terraces are defined based upon morphology, elevation and dating, together with fieldwork and high-resolution satellite analysis. The majority of the CRN model ages fall within narrow ranges (<2 ka) on the four main terraces (T1, T2, T3 and T3′), and allow a detailed terrace chronology. Bounds on the terrace ages and offsets of 5 independent terraces yield consistent slip-rate estimates. The long-term slip-rate of 13.9 ± 1.1 mm/yr is defined at the 95% confidence level, as the joint rate probability distribution of the rate derived from each independent terrace. It falls within the bounds of all the rates defined on the central Altyn Tagh Fault between the Cherchen He (86.4°E) and Akato Tagh (~88°E) sites. This rate is ~10 mm/yr less than the upper rate determined near Tura at ~87°E, in keeping with the inference of an eastward decreasing rate due to progressive loss of slip to thrusts branching off the fault southwards but it is greater than the 9 ± 4 mm/yr rate determined at ~90°E by GPS surveys and other geodetic short-term rates defined elsewhere along the ATF. Furthermore, whether such disparate rates will ultimately be reconciled by a better understanding of fault mechanics, resolved transient deformations during the seismic cycle or by more accurate measurements made with either approach remains an important issue.

  4. Maximum Magnitude in Relation to Mapped Fault Length and Fault Rupture

    NASA Astrophysics Data System (ADS)

    Black, N.; Jackson, D.; Rockwell, T.

    2004-12-01

    Earthquake hazard zones are highlighted using known fault locations and an estimate of the fault's maximum magnitude earthquake. Magnitude limits are commonly determined from fault geometry, which is dependent on fault length. Over the past 30 years it has become apparent that fault length is often poorly constrained and that a single event can rupture across several individual fault segments. In this study fault geometries are analyzed before and after several moderate to large magnitude earthquakes to determine how well fault length can accurately assess seismic hazard. Estimates of future earthquake magnitudes are often inferred from prior determinations of fault length, but use magnitude regressions based on rupture length. However, rupture length is not always limited to the previously estimated fault length or contained on a single fault. Therefore, the maximum magnitude for a fault may be underestimated, unless the geometry and segmentation of faulting is completely understood. This study examines whether rupture/fault length can be used to accurately predict the maximum magnitude for a given fault. We examine earthquakes greater than 6.0 that occurred after 1970 in Southern California. Geologic maps, fault evaluation reports, and aerial photos that existed prior to these earthquakes are used to obtain the pre-earthquake fault lengths. Pre-earthquake fault lengths are compared with rupture lengths to determine: 1) if fault lengths are the same before and after the ruptures and 2) to constrain the geology and geometry of ruptures that propagated beyond the originally recognized endpoints of a mapped fault. The ruptures examined in this study typically follow one of the following models. The ruptures are either: 1) contained within the dimensions of the original fault trace, 2) break through one or both end points of the originally mapped fault trace, or 3) break through multiple faults, connecting segments into one large fault line. No rupture simply broke a

  5. Timing of large earthquakes during the past 500 years along the Santa Cruz Mountains segment of the San Andreas fault at Mill Canyon, near Watsonville, California

    USGS Publications Warehouse

    Fumal, Thomas E.

    2012-01-01

    A paleoseismic investigation across the Santa Cruz Mountains section of the San Andreas fault at Mill Canyon indicates that four surface‐rupturing earthquakes have occurred there during the past ~500  years. At this site, right‐lateral fault slip has moved a low shutter ridge across the mouth of the canyon, ponding latest Holocene sediments. These alluvial deposits are deformed along a narrow zone of faulting. There is excellent evidence for a 1906 (M 7.8) and three earlier earthquakes consisting of well‐developed fissures, scarps, and colluvial wedges. Deformation resulting from the earlier earthquakes is comparable to that from 1906, suggesting they also were large‐magnitude events. The earthquake prior to 1906 occurred either about A.D. 1750 (1711–1770) or A.D. 1855 (1789–1904), depending on assumptions incorporated into two alternative OxCal models. If the later age range is correct, then the earthquake may have been a historical early‐to‐mid‐nineteenth‐century earthquake, possibly the A.D. 1838 earthquake. Both models are viable, and there is no way to select one over the other with the available data. Two earlier earthquakes occurred about A.D. 1690 (1660–1720) and A.D. 1522 (1454–1605). Using OxCal, recalculation of the age of the reported penultimate earthquake reported from the Grizzly Flat site, located about 10 km northwest of Mill Canyon, indicates it occurred about A.D. 1105–1545, earlier than any of the past three earthquakes, and possibly correlates to the fourth earthquake at Mill Canyon.

  6. Structure Segmentation and Transfer Faults in the Marcellus Shale, Clearfield County, Pennsylvania: Implications for Gas Recovery Efficiency and Risk Assessment Using 3D Seismic Attribute Analysis

    NASA Astrophysics Data System (ADS)

    Roberts, Emily D.

    The Marcellus Shale has become an important unconventional gas reservoir in the oil and gas industry. Fractures within this organic-rich black shale serve as an important component of porosity and permeability useful in enhancing production. Horizontal drilling is the primary approach for extracting hydrocarbons in the Marcellus Shale. Typically, wells are drilled perpendicular to natural fractures in an attempt to intersect fractures for effective hydraulic stimulation. If the fractures are contained within the shale, then hydraulic fracturing can enhance permeability by further breaking the already weakened rock. However, natural fractures can affect hydraulic stimulations by absorbing and/or redirecting the energy away from the wellbore, causing a decreased efficiency in gas recovery, as has been the case for the Clearfield County, Pennsylvania study area. Estimating appropriate distances away from faults and fractures, which may limit hydrocarbon recovery, is essential to reducing the risk of injection fluid migration along these faults. In an attempt to mitigate the negative influences of natural fractures on hydrocarbon extraction within the Marcellus Shale, fractures were analyzed through the aid of both traditional and advanced seismic attributes including variance, curvature, ant tracking, and waveform model regression. Through the integration of well log interpretations and seismic data, a detailed assessment of structural discontinuities that may decrease the recovery efficiency of hydrocarbons was conducted. High-quality 3D seismic data in Central Pennsylvania show regional folds and thrusts above the major detachment interval of the Salina Salt. In addition to the regional detachment folds and thrusts, cross-regional, northwest-trending lineaments were mapped. These lineaments may pose a threat to hydrocarbon productivity and recovery efficiency due to faults and fractures acting as paths of least resistance for induced hydraulic stimulation fluids

  7. Fault displacement hazard for strike-slip faults

    USGS Publications Warehouse

    Petersen, M.D.; Dawson, T.E.; Chen, R.; Cao, T.; Wills, C.J.; Schwartz, D.P.; Frankel, A.D.

    2011-01-01

    In this paper we present a methodology, data, and regression equations for calculating the fault rupture hazard at sites near steeply dipping, strike-slip faults. We collected and digitized on-fault and off-fault displacement data for 9 global strikeslip earthquakes ranging from moment magnitude M 6.5 to M 7.6 and supplemented these with displacements from 13 global earthquakes compiled byWesnousky (2008), who considers events up to M 7.9. Displacements on the primary fault fall off at the rupture ends and are often measured in meters, while displacements on secondary (offfault) or distributed faults may measure a few centimeters up to more than a meter and decay with distance from the rupture. Probability of earthquake rupture is less than 15% for cells 200 m??200 m and is less than 2% for 25 m??25 m cells at distances greater than 200mfrom the primary-fault rupture. Therefore, the hazard for off-fault ruptures is much lower than the hazard near the fault. Our data indicate that rupture displacements up to 35cm can be triggered on adjacent faults at distances out to 10kmor more from the primary-fault rupture. An example calculation shows that, for an active fault which has repeated large earthquakes every few hundred years, fault rupture hazard analysis should be an important consideration in the design of structures or lifelines that are located near the principal fault, within about 150 m of well-mapped active faults with a simple trace and within 300 m of faults with poorly defined or complex traces.

  8. Off-fault tip splay networks: A genetic and generic property of faults indicative of their long-term propagation

    NASA Astrophysics Data System (ADS)

    Perrin, Clément; Manighetti, Isabelle; Gaudemer, Yves

    2016-01-01

    We use fault maps and fault propagation evidences available in the literature to examine geometrical relations between parent faults and off-fault splays. The population includes 47 worldwide crustal faults with lengths from millimetres to thousands of kilometres and of different slip modes. We show that fault splays form adjacent to any propagating fault tip, whereas they are absent at non-propagating fault ends. Independent of fault length, slip mode, context, etc., tip splay networks have a similar fan shape widening in direction of long-term propagation, a similar relative length and width (∼ 30 and ∼ 10% of parent fault length, respectively), and a similar range of mean angles to parent fault (10-20°). We infer that tip splay networks are a genetic and a generic property of faults indicative of their long-term propagation. Their generic geometrical properties suggest they result from generic off-fault stress distribution at propagating fault ends.

  9. The property of fault zone and fault activity of Shionohira Fault, Fukushima, Japan

    NASA Astrophysics Data System (ADS)

    Seshimo, K.; Aoki, K.; Tanaka, Y.; Niwa, M.; Kametaka, M.; Sakai, T.; Tanaka, Y.

    2015-12-01

    The April 11, 2011 Fukushima-ken Hamadori Earthquake (hereafter the 4.11 earthquake) formed co-seismic surface ruptures trending in the NNW-SSE direction in Iwaki City, Fukushima Prefecture, which were newly named as the Shionohira Fault by Ishiyama et al. (2011). This earthquake was characterized by a westward dipping normal slip faulting, with a maximum displacement of about 2 m (e.g., Kurosawa et al., 2012). To the south of the area, the same trending lineaments were recognized to exist even though no surface ruptures occurred by the earthquake. In an attempt to elucidate the differences of active and non-active segments of the fault, this report discusses the results of observation of fault outcrops along the Shionohira Fault as well as the Coulomb stress calculations. Only a few outcrops have basement rocks of both the hanging-wall and foot-wall of the fault plane. Three of these outcrops (Kyodo-gawa, Shionohira and Betto) were selected for investigation. In addition, a fault outcrop (Nameishi-minami) located about 300 m south of the southern tip of the surface ruptures was investigated. The authors carried out observations of outcrops, polished slabs and thin sections, and performed X-ray diffraction (XRD) to fault materials. As a result, the fault zones originating from schists were investigated at Kyodo-gawa and Betto. A thick fault gouge was cut by a fault plane of the 4.11 earthquake in each outcrop. The fault materials originating from schists were fault bounded with (possibly Neogene) weakly deformed sandstone at Shionohira. A thin fault gouge was found along the fault plane of 4.11 earthquake. A small-scale fault zone with thin fault gouge was observed in Nameishi-minami. According to XRD analysis, smectite was detected in the gouges from Kyodo-gawa, Shionohira and Betto, while not in the gouge from Nameishi-minami.

  10. Barriers to faulting in the Basin-Range province: evidence from the Sou Hills transverse block

    SciTech Connect

    Fonseca, J.E.

    1985-01-01

    Transverse structural blocks may inhibit the propagation of fault ruptures in the Basin-Range province. The Sou Hills, between Dixie and Pleasant Valleys, is a block of uplifted Tertiary bedrock transverse to the NNE-SSW trend of the central Nevada seismic belt. Three lines of evidence indicate that offset due to normal faulting is much less in the Sou Hills compared to adjacent segments of the seismic belt. First, estimates of total late Cenozoic offsets of pre-extension basalts show that the total offset is less in the Sou Hills. Second, analyses of landforms that reflect rates of relative uplift show that Quaternary tectonic activity on range-bounding faults declines where faults join the Sou Hills. Third, measurements of late Quaternary fault scarps show that individual rupture segments in the Sou Hills are shorter in length and have smaller displacements compared to the nearly continuous ruptures of several meters offset found along the Tobin and Stillwater Ranges to the north and south. The Sou Hills rupture pattern is distinctive: ruptures are dispersed over a wide zone rather than being concentrated along well-defined range fronts. Normal faulting patterns produced by the 1915 Pleasant Valley, Nevada and the 1983 Borah Peak, Idaho earthquakes indicate that a discontinuous, spatially dispersed faulting style typifies ruptures which die out in transverse bedrock features. These historic analogues support a model for prehistoric faulting in which ruptures have repeatedly died out in the Sou Hills. Transverse blocks such as the Sou Hills appear to present barriers to propagating ruptures.

  11. SEISMOLOGY: Watching the Hayward Fault.

    PubMed

    Simpson, R W

    2000-08-18

    The Hayward fault, located on the east side of the San Francisco Bay, represents a natural laboratory for seismologists, because it does not sleep silently between major earthquakes. In his Perspective, Simpson discusses the study by Bürgmann et al., who have used powerful new techniques to study the fault. The results indicate that major earthquakes cannot originate in the northern part of the fault. However, surface-rupturing earthquakes have occurred in the area, suggesting that they originated to the north or south of the segment studied by Bürgmann et al. Fundamental questions remain regarding the mechanism by which plate tectonic stresses are transferred to the Hayward fault.

  12. Earthquakes and fault creep on the northern San Andreas fault

    USGS Publications Warehouse

    Nason, R.

    1979-01-01

    At present there is an absence of both fault creep and small earthquakes on the northern San Andreas fault, which had a magnitude 8 earthquake with 5 m of slip in 1906. The fault has apparently been dormant after the 1906 earthquake. One possibility is that the fault is 'locked' in some way and only produces great earthquakes. An alternative possibility, presented here, is that the lack of current activity on the northern San Andreas fault is because of a lack of sufficient elastic strain after the 1906 earthquake. This is indicated by geodetic measurements at Fort Ross in 1874, 1906 (post-earthquake), and 1969, which show that the strain accumulation in 1969 (69 ?? 10-6 engineering strain) was only about one-third of the strain release (rebound) in the 1906 earthquake (200 ?? 10-6 engineering strain). The large difference in seismicity before and after 1906, with many strong local earthquakes from 1836 to 1906, but only a few strong earthquakes from 1906 to 1976, also indicates a difference of elastic strain. The geologic characteristics (serpentine, fault straightness) of most of the northern San Andreas fault are very similar to the characteristics of the fault south of Hollister, where fault creep is occurring. Thus, the current absence of fault creep on the northern fault segment is probably due to a lack of sufficient elastic strain at the present time. ?? 1979.

  13. Development of Relations of Stream Stage to Channel Geometry and Discharge for Stream Segments Simulated with Hydrologic Simulation Program-Fortran (HSPF), Chesapeake Bay Watershed and Adjacent Parts of Virginia, Maryland, and Delaware

    USGS Publications Warehouse

    Moyer, Douglas; Bennett, Mark

    2007-01-01

    The U.S. Geological Survey (USGS), U.S. Environmental Protection Agency (USEPA), Chesapeake Bay Program (CBP), Interstate Commission for the Potomac River Basin (ICPRB), Maryland Department of the Environment (MDE), Virginia Department of Conservation and Recreation (VADCR), and University of Maryland (UMD) are collaborating to improve the resolution of the Chesapeake Bay Regional Watershed Model (CBRWM). This watershed model uses the Hydrologic Simulation Program-Fortran (HSPF) to simulate the fate and transport of nutrients and sediment throughout the Chesapeake Bay watershed and extended areas of Virginia, Maryland, and Delaware. Information from the CBRWM is used by the CBP and other watershed managers to assess the effectiveness of water-quality improvement efforts as well as guide future management activities. A critical step in the improvement of the CBRWM framework was the development of an HSPF function table (FTABLE) for each represented stream channel. The FTABLE is used to relate stage (water depth) in a particular stream channel to associated channel surface area, channel volume, and discharge (streamflow). The primary tool used to generate an FTABLE for each stream channel is the XSECT program, a computer program that requires nine input variables used to represent channel morphology. These input variables are reach length, upstream and downstream elevation, channel bottom width, channel bankfull width, channel bankfull stage, slope of the floodplain, and Manning's roughness coefficient for the channel and floodplain. For the purpose of this study, the nine input variables were grouped into three categories: channel geometry, Manning's roughness coefficient, and channel and floodplain slope. Values of channel geometry for every stream segment represented in CBRWM were obtained by first developing regional regression models that relate basin drainage area to observed values of bankfull width, bankfull depth, and bottom width at each of the 290 USGS

  14. Fault interaction near Hollister, California

    NASA Astrophysics Data System (ADS)

    Mavko, Gerald M.

    1982-09-01

    A numerical model is used to study fault stress and slip near Hollister, California. The geometrically complex system of interacting faults, including the San Andreas, Calaveras, Sargent, and Busch faults, is approximated with a two-dimensional distribution of short planar fault segments in an elastic medium. The steady stress and slip rate are simulated by specifying frictional strength and stepping the remote stress ahead in time. The resulting computed fault stress is roughly proportional to the observed spatial density of small earthquakes, suggesting that the distinction between segments characterized by earthquakes and those with aseismic creep results, in part, from geometry. A nosteady simulation is made by introducing, in addition, stress drops for individual moderate earthquakes. A close fit of observed creep with calculated slip on the Calaveras and San Andreas faults suggests that many changes in creep rate (averaged over several months) are caused by local moderate earthquakes. In particular, a 3-year creep lag preceding the August 6, 1979, Coyote Lake earthquake on the Calaveras fault seems to have been a direct result of the November 28, 1974, Thanksgiving Day earthquake on the Busch fault. Computed lags in slip rate preceding some other moderate earthquakes in the area are also due to earlier earthquakes. Although the response of the upper 1 km of the fault zone may cause some individual creep events and introduce delays in others, the long-term rate appears to reflect deep slip.

  15. Fault interaction near Hollister, California

    SciTech Connect

    Mavko, G.M.

    1982-09-10

    A numerical model is used to study fault stress slip near Hollister, California. The geometrically complex system of interacting faults, including the San Andreas, Calaveras, Sargent, and Busch faults, is approximated with a two-dimensional distribution of short planar fault segments in an elastic medium. The steady stress and slip rate are simulated by specifying frictional strength and stepping the remote stress ahead in time. The resulting computed fault stress is roughly proportional to the observed spatial density of small earthquakes, suggesting that the distinction between segments characterized by earthquakes and those with aseismic creep results, in part, from geometry. A nonsteady simulation is made by introducing, in addition, stress drops for individual moderate earthquakes. A close fit of observed creep with calculated slip on the Calaveras and San Andreas faults suggests that many changes in creep rate (averaged over several months) are caused by local moderate earthquakes. In particular, a 3-year creep lag preceding the August 6, 1979, Coyote Lake earthquake on the Calaveras fault seems to have been a direct result of the November 28, 1974, Thanksgiving Day earthquake on the Busch fault. Computed lags in slip rate preceding some other moderate earthquakes in the area are also due to earlier earthquakes. Although the response of the upper 1 km of the fault zone may cause some individual creep events and introduce delays in others, the long-term rate appears to reflect deep slip.

  16. Geology and seismotectonics of the North-Anatolian Fault in the Sea of Marmara: implications for seismic hazards

    NASA Astrophysics Data System (ADS)

    Gasperini, Luca; Cedro, Vincenzo; Polonia, Alina; Cruise Party, Marmara

    2016-04-01

    Based on high-resolution multibeam and seismic reflection data recently collected and analysed in the frame of Marsite (New Directions in Seismic Hazard Assessment through Focused Earth Observation in the Marmara Supersite) EC FP7 Project, in conjunction with a large set of geophysical and geological data collected starting from 1999, we compiled a new morphotectonic map of the submerged part of the North-Anatolian Fault system (NAF) in the Sea of Marmara. Data analysis allowed us to recognize active fault segments and their activity at the scale of 10 ka, taking as stratigraphic reference the base of the latest marine ingression, which constitutes a clear marker in the sedimentary sequence of the Sea of Marmara. This is mainly due to the fact the Sea of Marmara was a fresh water lake during the Last Glacial Maximum, and switched to a marine environment when the global sea level reached to the -85 m relative to present day and crossed the Dardanelles sill during the transgression. The passage from lacustrine to marine environment is marked by a typical unconformity in high-resolution seismic profiles, which can be correlated over the entire Marmara basin. According to the average recurrence time for major earthquake along the NAF, the time interval of 10 ka should include several earthquake cycle and is representative of the seismotectonic behavior of the fault at geological time scales. Given the relatively high deformation rates relative to in relative to sediment supply, most active tectonic structures have a morphological expression at the seafloor. This allowed us to correlate deformations from a seismic section to the adjacent. Fault strands not affecting the Holocene sequence were considered inactive. Three types of deformation patterns were observed and classified: almost purely E-W oriented strike-slip segments; NE-SW oriented trans-pressional structures; NW-SE trending trans-tensional features. Segmentation of the so-called Main Marmara Fault in the Sea

  17. Geodynamic significance of the TRM segment in the East African Rift (W-Tanzania): Active tectonics and paleostress in the Ufipa plateau and Rukwa basin

    NASA Astrophysics Data System (ADS)

    Delvaux, D.; Kervyn, F.; Macheyeki, A. S.; Temu, E. B.

    2012-04-01

    The Tanganyika-Rukwa-Malawi (TRM) rift segment in western Tanzania is a key sector for understanding the opening dynamics of the East African rift system (EARS). In an oblique opening model, it is considered as a dextral transfer fault zone that accommodates the general opening of the EARS in an NW-SE direction. In an orthogonal opening model, it accommodates pure dip-slip normal faulting with extension orthogonal to the rift segments and a general E-W extension for the entire EARS. The central part of the TRM rift segment is well exposed in the Ufipa plateau and Rukwa basin, within the Paleoproterozoic Ubende belt. It is also one of the most seismically active regions of the EARS. We investigated the active tectonic architecture and paleostress evolution of the Ufipa plateau and adjacent Rukwa basin and in order to define their geodynamic role in the development of the EARS and highlight their pre-rift brittle tectonic history. The active fault architecture, fault-kinematic analysis and paleostress reconstruction show that the recent to active fault systems that control the rift structure develop in a pure extensional setting with extension direction orthogonal to the trend of the TRM segment. Two pre-rift brittle events are evidenced. An older brittle thrusting is related to the interaction between the Bangweulu block and the Tanzanian craton during the late Pan-African (early Paleozoic). It was followed by a transpressional inversion during the early Mesozoic. This inversion stage is the best expressed in the field and caused dextral strike-slip faulting along the fault systems that now control the major rift structures. It has been erroneously interpreted as related to the late Cenozoic EARS which instead is characterized by pure normal faulting (our third and last stress stage).

  18. Electro-Optic Segment-Segment Sensors for Radio and Optical Telescopes

    NASA Technical Reports Server (NTRS)

    Abramovici, Alex

    2012-01-01

    A document discusses an electro-optic sensor that consists of a collimator, attached to one segment, and a quad diode, attached to an adjacent segment. Relative segment-segment motion causes the beam from the collimator to move across the quad diode, thus generating a measureable electric signal. This sensor type, which is relatively inexpensive, can be configured as an edge sensor, or as a remote segment-segment motion sensor.

  19. Block model of western US kinematics from inversion of geodetic, fault slip, and earthquake data

    NASA Astrophysics Data System (ADS)

    McCaffrey, R.

    2003-12-01

    The active deformation of the southwestern US (30° to 41° N) is represented by a finite number of rotating, elastic spherical caps. Horizontal GPS velocities (1583), fault slip rates (94), and earthquake slip vectors (116) are inverted for block angular velocities, locking on block-bounding faults, and the rotation of individual GPS velocity fields relative to North America. GPS velocities are modeled as a combination of rigid block rotations and elastic strain rates resulting from interactions of adjacent blocks across bounding faults. The resulting Pacific - North America pole is indistinguishable from that of Beavan et al. (2001) and satisfies spreading in the Gulf of California and earthquake slip vectors in addition to GPS. The largest blocks, the Sierra Nevada - Great Valley and the eastern Basin and Range, show internal strain rates, after removing the elastic component, of only a few nanostrain/a, demonstrating long term approximately rigid behavior. Most fault slip data are satisfied except that the San Jacinto fault appears to be significantly faster than inferred from geology while the Coachella and San Bernardino segments of the San Andreas fault are slower, suggesting the San Andreas system is straightening out in Southern California. Vertical axis rotation rates for most blocks are clockwise and in magnitude more like the Pacific than North America. One exception is the eastern Basin and Range (242° E to 248° E) which rotates slowly anticlockwise about a pole offshore Baja.

  20. Fault geometry and slip distribution of the 1891 Nobi great earthquake (M = 8.0) with the oldest survey data sets in Japan

    NASA Astrophysics Data System (ADS)

    Takano, K.; Kimata, F.

    2010-12-01

    This study reexamines the ground deformation and fault slip model of the 1891 Nobi great earthquake (M = 8.0), central Japan. At the earthquake, three faults of Nukumi, Neodani and Umehara ruptured the ground surface with maximum of 8 m in the horizontal direction and 6 m in the vertical direction along the 80 km length [Koto, 1893; Matsuda, 1974]. Additionally, the Gifu-Ichinomiya line stretching toward south from Gifu is discussed as the buried fault of the Nobi earthquake, because of the vertical deformation and the high collapse rates along the line and wave propagation [Mikumo and Ando, 1976; Nakano et al., 2007]. We reevaluate two geodetic data sets of triangulation and leveling around the Umehara fault in 1885-1890 and 1894-1908 that were obtained from the Japanese Imperial Land Survey in the General Staff Office of the Imperial Army (the present Geospatial Information Authority of Japan); these data sets consist of displacements calculated from the net adjustment of triangulation and leveling surveys carried out before and after the Nobi earthquake. Co-seismic displacements are detected as southeastward displacements and uplifts are detected in the southwest block the Umehara fault. The maximum displacements and uplifts are up to 1.7 m and 0.74 m, respectively. We estimated the coseismic slip distribution of the faults by analyzing our data set. The geometry of the fault planes was adopted from the earthquake fault of this area. The remaining parameters are determined using a quasi-Newton nonlinear optimization algorithm. The best fit to the data is obtained from seven segments of the faults along the sections running Nukumi, Neodani and Umehara faults. The estimated uniform-slip elastic dislocation model consists of seven adjacent planes. The fault slips are up to 3.8 m. Because it can suitably explain the coseismic deformation due to seven earthquake source faults, the earthquake source fault is not admitted under the Gifu-Ichinomiya line.

  1. Evidence for slip partitioning and bimodal slip behavior on a single fault: Surface slip characteristics of the 2013 Mw7.7 Balochistan, Pakistan earthquake

    NASA Astrophysics Data System (ADS)

    Barnhart, W. D.; Briggs, R. W.; Reitman, N. G.; Gold, R. D.; Hayes, G. P.

    2015-06-01

    Deformation is commonly accommodated by strain partitioning on multiple, independent strike-slip and dip-slip faults in continental settings of oblique plate convergence. As a corollary, individual faults tend to exhibit one sense of slip - normal, reverse, or strike-slip - until whole-scale changes in boundary conditions reactivate preexisting faults in a new deformation regime. In this study, we show that a single continental fault may instead partition oblique strain by alternatively slipping in a strike-slip or a dip-slip sense during independent fault slip events. We use 0.5 m resolution optical imagery and sub-pixel correlation analysis of the 200 + km 2013 Mw7.7 Balochistan, Pakistan earthquake to document co-seismic surface slip characteristics and Quaternary tectonic geomorphology along the causative Hoshab fault. We find that the 2013 earthquake, which involved a ∼6:1 strike-slip to dip-slip ratio, ruptured a structurally segmented fault. Quaternary geomorphic indicators of gross fault-zone morphology reveal both reverse-slip and strike-slip deformation in the rupture area of the 2013 earthquake that varies systematically along fault strike despite nearly pure strike-slip motion in 2013. Observations of along-strike variations in range front relief and geomorphic offsets suggest that the Hoshab fault accommodates a substantial reverse component of fault slip in the Quaternary, especially along the southern section of the 2013 rupture. We surmise that Quaternary bimodal slip along the Hoshab fault is promoted by a combination of the arcuate geometry of the Hoshab fault, the frictional weakness of the Makran accretionary prism, and time variable loading conditions from adjacent earthquakes and plate interactions.

  2. Evidence for Late Oligocene-Early Miocene episode of transtension along San Andreas Fault system in central California

    SciTech Connect

    Stanley, R.G.

    1986-04-01

    The San Andreas is one of the most intensely studied fault systems in the world, but many aspects of its kinematic history remain controversial. For example, the period from the late Eocene to early Miocene is widely believed to have been a time of negligible strike-slip movement along the San Andreas fault proper, based on the rough similarity of offset of the Eocene Butano-Point of rocks Submarine Fan, the early Miocene Pinnacles-Neenach volcanic center, and an early Miocene shoreline in the northern Gabilan Range and San Emigdio Mountains. Nonetheless, evidence indicates that a late Oligocene-early Miocene episode of transtension, or strike-slip motion with a component of extension, occurred within the San Andreas fault system. The evidence includes: (1) about 22-24 Ma, widespread, synchronous volcanic activity occurred at about 12 volcanic centers along a 400-km long segment of the central California coast; (2) most of these volcanic centers are located along faults of the San Andreas system, including the San Andreas fault proper, the San Gregorio-Hosgri fault, and the Zayante-Vergeles fault, suggesting that these and other faults were active and served as conduits for magmas rising from below; (3) during the late Oligocene and early Miocene, a pull-apart basin developed adjacent to the San Andreas fault proper in the La Honda basin near Santa Cruz; and (4) during the late Oligocene and early Miocene, active faulting, rapid subsidence, and marine transgression occurred in the La Honda and other sedimentary basins in central California. The amount of right-lateral displacement along the San Andreas fault proper during this transtentional episode is unknown but was probably about 7.5-35 km, based on model studies of pull-apart basin formation. This small amount of movement is well within the range of error in published estimates of the offset of the Eocene to early Miocene geologic features noted.

  3. Coulomb stress change on surrounding faults by the January 12, 2010, Haiti earthquake

    NASA Astrophysics Data System (ADS)

    Symithe, S. J.; Calais, E.; Freed, A. M.; Haase, J. S.

    2011-12-01

    assumed. For average values of the coefficient of friction (0.4) we find a large CFS decrease in the segment of the Enriquillo Fault that is adjacent to the 2010 rupture. For the Trois Baies fault, located to the northwest of the rupture between the Gonâve island and the Southern Peninsula and striking N120°, we find a modest CFS increase (~0.1 bar) on the shallow portion of the segment and a ~0.5 bar CFS increase on the deeper portion. There are no significant CFS changes on most other nearby faults, such as the Neiba-Matheux fault to the north.

  4. Segmented rail linear induction motor

    DOEpatents

    Cowan, Jr., Maynard; Marder, Barry M.

    1996-01-01

    A segmented rail linear induction motor has a segmented rail consisting of a plurality of nonferrous electrically conductive segments aligned along a guideway. The motor further includes a carriage including at least one pair of opposed coils fastened to the carriage for moving the carriage. A power source applies an electric current to the coils to induce currents in the conductive surfaces to repel the coils from adjacent edges of the conductive surfaces.

  5. Segmented rail linear induction motor

    DOEpatents

    Cowan, M. Jr.; Marder, B.M.

    1996-09-03

    A segmented rail linear induction motor has a segmented rail consisting of a plurality of nonferrous electrically conductive segments aligned along a guideway. The motor further includes a carriage including at least one pair of opposed coils fastened to the carriage for moving the carriage. A power source applies an electric current to the coils to induce currents in the conductive surfaces to repel the coils from adjacent edges of the conductive surfaces. 6 figs.

  6. Deformation rates across the San Andreas Fault system, central California determined by geology and geodesy

    NASA Astrophysics Data System (ADS)

    Titus, Sarah J.

    The San Andreas fault system is a transpressional plate boundary characterized by sub-parallel dextral strike-slip faults separating internally deformed crustal blocks in central California. Both geodetic and geologic tools were used to understand the short- and long-term partitioning of deformation in both the crust and the lithospheric mantle across the plate boundary system. GPS data indicate that the short-term discrete deformation rate is ˜28 mm/yr for the central creeping segment of the San Andreas fault and increases to 33 mm/yr at +/-35 km from the fault. This gradient in deformation rates is interpreted to reflect elastic locking of the creeping segment at depth, distributed off-fault deformation, or some combination of these two mechanisms. These short-term fault-parallel deformation rates are slower than the expected geologic slip rate and the relative plate motion rate. Structural analysis of folds and transpressional kinematic modeling were used to quantify long-term distributed deformation adjacent to the Rinconada fault. Folding accommodates approximately 5 km of wrench deformation, which translates to a deformation rate of ˜1 mm/yr since the start of the Pliocene. Integration with discrete offset on the Rinconada fault indicates that this portion of the San Andreas fault system is approximately 80% strike-slip partitioned. This kinematic fold model can be applied to the entire San Andreas fault system and may explain some of the across-fault gradient in deformation rates recorded by the geodetic data. Petrologic examination of mantle xenoliths from the Coyote Lake basalt near the Calaveras fault was used to link crustal plate boundary deformation at the surface with models for the accommodation of deformation in the lithospheric mantle. Seismic anisotropy calculations based on xenolith petrofabrics suggest that an anisotropic mantle layer thickness of 35-85 km is required to explain the observed shear wave splitting delay times in central

  7. Slip-Rate on the Haiyuan Fault (Gansu, China), Over Time Scales of 10 yr to 10 kyr

    NASA Astrophysics Data System (ADS)

    Lasserre, C.; Cavalié, O.; Doin, M.; Peltzer, G.; Sun, J.; Shen, Z.; Wang, Q.; Xu, X.

    2006-12-01

    The tectonics of the northern Tibetan plateau is characterized by large strike-slip and thrust faults, accommodating the deformation induced by the collision between India and Asia. Estimating and comparing slip-rates on these faults over different time scales is important to better understand the strain accumulation and release processes along faults, as well as the mechanisms involved in the deformation of the lithosphere. We use SAR interferometry to measure the current, interseismic strain along the Haiyuan fault. Located at the northeastern edge of the Tibetan plateau, this left-lateral fault and an associated thrust system have been the locus of two M~8 earthquakes in 1920 and 1927, respectively. Our data cover the Tianzhu seismic gap segment along the central part of the Haiyuan fault between the 1920 and 1927 rupture zones. The Holocene slip rate along the gap has been estimated to 12±4 mm/yr, from offset terraces and carbon dating (Lasserre et al., 1999). We processed 28 ERS radar scenes, acquired between 1993 and 1998 along two adjacent tracks on descending orbits, between longitudes 102.6°E and 105.3°E, into interferograms. The phase coherence is good over most of the imaged area, except in the Maomao Shan and Hasi Shan, and in the Gobi desert to the north. We corrected for orbital errors by removing a linear form in range and azimuth from the phase. An empirical correction based on the local phase-elevation correlation was used to remove tropospheric propagation delays. The corrected interferograms from the two adjacent satellite tracks were stacked to form two line-of-sight average velocity maps. These independent observations show a consistent deformation signal across the Haiyuan fault. The two stacks are subsequently combined into a fault-parallel velocity map covering the overlapping section of the two tracks, assuming a purely horizontal motion along the fault. The resulting fault-parallel velocity field shows a sharp concentration of

  8. Tool for Viewing Faults Under Terrain

    NASA Technical Reports Server (NTRS)

    Siegel, Herbert, L.; Li, P. Peggy

    2005-01-01

    Multi Surface Light Table (MSLT) is an interactive software tool that was developed in support of the QuakeSim project, which has created an earthquake- fault database and a set of earthquake- simulation software tools. MSLT visualizes the three-dimensional geometries of faults embedded below the terrain and animates time-varying simulations of stress and slip. The fault segments, represented as rectangular surfaces at dip angles, are organized into collections, that is, faults. An interface built into MSLT queries and retrieves fault definitions from the QuakeSim fault database. MSLT also reads time-varying output from one of the QuakeSim simulation tools, called "Virtual California." Stress intensity is represented by variations in color. Slips are represented by directional indicators on the fault segments. The magnitudes of the slips are represented by the duration of the directional indicators in time. The interactive controls in MSLT provide a virtual track-ball, pan and zoom, translucency adjustment, simulation playback, and simulation movie capture. In addition, geographical information on the fault segments and faults is displayed on text windows. Because of the extensive viewing controls, faults can be seen in relation to one another, and to the terrain. These relations can be realized in simulations. Correlated slips in parallel faults are visible in the playback of Virtual California simulations.

  9. Surface expressed subduction earthquake segment boundary and its verification in seismological data

    NASA Astrophysics Data System (ADS)

    Sobiesiak, M.; Victor, P.; Oncken, O.; Eggert, S.

    2008-12-01

    One of the key questions in seismotectonics is what determines the size of an earthquake rupture and whether the geological and tectonic structure has an influence on rupture dynamics. We have found evidence for a subduction segment boundary on Mejillones Peninsula in Northern Chile expressed in topographic features which form an E-W transect over the peninsula in the area around 23.3°S. This transect subdivides the peninsula in a northern and southern part exhibiting differences in geological and tectonic parameters. Stratigraphic data, morphotectonic structures, fault patterns and age of deformation as well as the coastal uplift on both parts have been examined and showed that the transect might act as a "hinge" line or segment boundary provided that it is a persistent feature over various seismic cycles. Confirmation for this interpretation is coming from seismological data particularly from the intensive study of the aftershock sequence of the M8.0, 1995, Antofagasta earthquake. The main shock hypocenter calculations reflecting the start of the rupture are all located in the area of the proposed segment boundary. Several E-W aligned aftershock hypocentres with strike slip focal mechanism are also congruent with the "hinge"-line over Mejillones Peninsula. Furthermore, a number of seismological parameters, like the seimic b-value, do change at the segment boundary. A very strong support for our hypothesis is coming from the recent M7.8, 2007, Tocopilla earthquake which ruptured the adjacent part of the seismogenic interface north of the Antofagasta earthquake fault plane. Preliminary hypocenter determinations of some aftershocks suggest that the Tocopilla fault plane ends where the Antofagasta fault plane starts, which is again congruent with the proposed segment boundary. In our presentation we would like to summarize the geological evidences and give some new results from the seismological studies of the Tocopilla earthquake.

  10. Deep reaching versus vertically restricted Quaternary normal faults: Implications on seismic potential assessment in tectonically active regions: Lessons from the middle Aterno valley fault system, central Italy

    NASA Astrophysics Data System (ADS)

    Falcucci, E.; Gori, S.; Moro, M.; Fubelli, G.; Saroli, M.; Chiarabba, C.; Galadini, F.

    2015-05-01

    We investigate the Middle Aterno Valley fault system (MAVF), a poorly investigated seismic gap in the central Apennines, adjacent to the 2009 L'Aquila earthquake epicentral area. Geological and paleoseismological analyses revealed that the MAVF evolved through hanging wall splay nucleation, its main segment moving at 0.23-0.34 mm/year since the Middle Pleistocene; the penultimate activation event occurred between 5388-5310 B.C. and 1934-1744 B.C., the last event after 2036-1768 B.C. and just before 1st-2nd century AD. These data define hard linkage (sensu Walsh and Watterson, 1991; Peacock et al., 2000; Walsh et al., 2003, and references therein) with the contiguous Subequana Valley fault segment, able to rupture in large magnitude earthquakes (up to 6.8), that did not rupture since about two millennia. By the joint analysis of geological observations and seismological data acquired during to the 2009 seismic sequence, we derive a picture of the complex structural framework of the area comprised between the MAVF, the Paganica fault (the 2009 earthquake causative fault) and the Gran Sasso Range. This sector is affected by a dense array of few-km long, closely and regularly spaced Quaternary normal fault strands, that are considered as branches of the MAVF northern segment. Our analysis reveals that these structures are downdip confined by a decollement represented by to the presently inactive thrust sheet above the Gran Sasso front limiting their seismogenic potential. Our study highlights the advantage of combining Quaternary geological field analysis with high resolution seismological data to fully unravel the structural setting of regions where subsequent tectonic phases took place and where structural interference plays a key role in influencing the seismotectonic context; this has also inevitably implications for accurately assessing seismic hazard of such structurally complex regions.

  11. Geometry Guided Segmentation

    NASA Astrophysics Data System (ADS)

    Dunn, Stanley M.; Liang, Tajen

    1989-03-01

    Our overall goal is to develop an image understanding system for automatically interpreting dental radiographs. This paper describes the module that integrates the intrinsic image data to form the region adjacency graph that represents the image. The specific problem is to develop a robust method for segmenting the image into small regions that do not overlap anatomical boundaries. Classical algorithms for finding homogeneous regions (i.e., 2 class segmentation or connected components) will not always yield correct results since blurred edges can cause adjacent anatomical regions to be labeled as one region. This defect is a problem in this and other applications where an object count is necessary. Our solution to the problem is to guide the segmentation by intrinsic properties of the constituent objects. The module takes a set of intrinsic images as arguments. A connected components-like algorithm is performed, but the connectivity relation is not 4- or 8-neighbor connectivity in binary images; the connectivity is defined in terms of the intrinsic image data. We shall describe both the classical method and the modified segmentation procedures, and present experiments using both algorithms. Our experiments show that for the dental radiographs a segmentation using gray level data in conjunction with edges of the surfaces of teeth give a robust and reliable segmentation.

  12. Sequential and incremental formation of conjugate sets of faults

    NASA Astrophysics Data System (ADS)

    Zhao, Guozhu; Johnson, Arvid M.

    The evolution of a system of strike-slip faults in porous Entrada Sandstone of Arches National Park, Utah, is investigated here. The area includes domains of parallel faults, oriented either N30E or N60E, and domains of conjugate sets. The age relations indicate that conjugate faults do not form simultaneously, but that a few members of one set form and then are offset by a few members of a second set. Then, new members of the first set form and offset some members of the second set. In this way, a conjugate pattern is built up. Cross-cutting relations also indicate that individual faults do not form simultaneously along their lengths. The traces of individual faults are segmented, with individual segments ranging from 10 cm to 60 m. The cross-cutting age relations indicate that the individual faults form sequentially by longitudinal growth and coalescence of segments. In an area of two sets of conjugate faults, segments in the sets form alternately, so a segment in one set is older than some segments and younger than other segments in the other set. The field observations of temporal and geometrical relations among conjugate faults in porous sandstone are consistent with experimental observations of growing faults in clay. Domains of a single set of faults, the sequential growth of fault segments, and the alternating growth of two sets all have been observed in carefully controlled experiments by Reches. Members of one set of conjugate faults interfering with members of another set, recognized by Oertel, is reflected in multiple fault splays in the vicinity of intersecting faults. The similarity between the field and experimental observations suggests that the processes controlling these relations are not restricted to faulting in porous rocks.

  13. Geologic structure of Middle Mountain within the San Andreas Fault zone near Parkfield, California

    NASA Astrophysics Data System (ADS)

    Thayer, M. R.; Arrowsmith, R.; Young, J.; Fayon, A.; Rymer, M.

    2004-12-01

    Knowledge of the geometry and history of motion of rock bodies within fault zones such as the San Andreas fault (SAF) is essential input into mechanical models of earthquake rupture dynamics and fault evolution. The Parkfield segment of the SAF is the focus of significant geophysical characterization and borehole studies. In order to enhance the geologic information about the SAF structure in this area, we undertook an intensive high-resolution geologic mapping effort (1:6000 scale) of the Middle Mountain area (about 40 km^2). The geologic structure differs dramatically across the San Andreas fault zone. The northeast side contains numerous sub-parallel faults that likely accommodated significant strike slip motion. These high-angle faults bound granite, marble, and sedimentary rock slivers. The density and complexity of these faults increases toward the center of the fault zone. The Gold Hill reverse fault on the northeast side of the SAF is a low-angle southwest-dipping fault that locally displaces the older Tertiary Monterey Formation over the younger Tertiary Etchegoin Formation. Folds with axes trending parallel to the strike of the Gold Hill reverse fault are present within the hanging wall. The Plio-Pleistocene Paso Robles Formation dominates the southwest side of the SAF and is a formidable cover. Fault-bounded granitoid slivers are also present within the southwest terrain. One fault striking nearly normal to the SAF cuts rock units near the mid-section of Middle Mountain. To the northwest of this fault, older Tertiary formations are present. The folds within the hanging wall of the Gold Hill reverse fault and the reverse fault itself indicate SAF-normal shortening near the SAF zone. The Gold Hill fault most likely cuts the numerous high-angle sub-parallel faults at depth. With the northeastward-verging nature of this fault, the cross-section on the northeast side is a roughly hewn half-flower structure. The sedimentary basin into which the Paso Robles

  14. Fault finder

    DOEpatents

    Bunch, Richard H.

    1986-01-01

    A fault finder for locating faults along a high voltage electrical transmission line. Real time monitoring of background noise and improved filtering of input signals is used to identify the occurrence of a fault. A fault is detected at both a master and remote unit spaced along the line. A master clock synchronizes operation of a similar clock at the remote unit. Both units include modulator and demodulator circuits for transmission of clock signals and data. All data is received at the master unit for processing to determine an accurate fault distance calculation.

  15. All row, planar fault detection system

    DOEpatents

    Archer, Charles Jens; Pinnow, Kurt Walter; Ratterman, Joseph D; Smith, Brian Edward

    2013-07-23

    An apparatus, program product and method for detecting nodal faults may simultaneously cause designated nodes of a cell to communicate with all nodes adjacent to each of the designated nodes. Furthermore, all nodes along the axes of the designated nodes are made to communicate with their adjacent nodes, and the communications are analyzed to determine if a node or connection is faulty.

  16. Multi-directional fault detection system

    DOEpatents

    Archer, Charles Jens; Pinnow, Kurt Walter; Ratterman, Joseph D.; Smith, Brian Edward

    2010-11-23

    An apparatus, program product and method checks for nodal faults in a group of nodes comprising a center node and all adjacent nodes. The center node concurrently communicates with the immediately adjacent nodes in three dimensions. The communications are analyzed to determine a presence of a faulty node or connection.

  17. Multi-directional fault detection system

    DOEpatents

    Archer, Charles Jens; Pinnow, Kurt Walter; Ratterman, Joseph D.; Smith, Brian Edward

    2010-06-29

    An apparatus, program product and method checks for nodal faults in a group of nodes comprising a center node and all adjacent nodes. The center node concurrently communicates with the immediately adjacent nodes in three dimensions. The communications are analyzed to determine a presence of a faulty node or connection.

  18. Multi-directional fault detection system

    DOEpatents

    Archer, Charles Jens; Pinnow, Kurt Walter; Ratterman, Joseph D.; Smith, Brian Edward

    2009-03-17

    An apparatus, program product and method checks for nodal faults in a group of nodes comprising a center node and all adjacent nodes. The center node concurrently communicates with the immediately adjacent nodes in three dimensions. The communications are analyzed to determine a presence of a faulty node or connection.

  19. Paleomagnetic Definition of Crustal Segmentation, Quaternary Block Rotations and Limits on Earthquake Magnitudes in Northwestern Metropolitan Los Angeles

    NASA Astrophysics Data System (ADS)

    Levi, S.; Yeats, R. S.; Nabelek, J.

    2004-12-01

    Paleomagnetic studies of the Pliocene-Quaternary Saugus Formation, in the San Fernando Valley and east Ventura Basin, show that the crust is segmented into small domains, 10-20 km in linear dimension, identified by rotation of reverse-fault blocks. Two domains, southwest and adjacent to the San Gabriel fault, are rotated clockwise: 1) The Magic Mountain domain, 30 +/- 5 degrees, and 2) the Merrick syncline domain, 34 +/- 6 degrees. The Magic Mountain domain has rotated since 1 Ma. Both rotated sections occur in hangingwalls of active reverse faults: the Santa Susana and San Fernando faults, respectively. Two additional domains are unrotated: 1) The Van Norman Lake domain, directly south of the Santa Susana fault, and 2) the Soledad Canyon domain in the San Gabriel block immediately across the San Gabriel fault from Magic Mountain, suggesting that the San Gabriel fault might be a domain boundary. Plio-Pleistocene fragmentation and clockwise rotations continue at present, based on geodetic data, and represent crustal response to diffuse, oblique dextral shearing within the San Andreas fault system. The horizontal dimensions of the blocks are similar to the thickness of the seismogenic layer. The maximum magnitude of an earthquake based on this size of blocks is Mw = 6.7, comparable to the 1971 San Fernando and 1994 Northridge earthquakes and consistent with paleoseismic trenching and surface ruptures of the 1971 earthquake. The paleomagnetic results suggest that the blocks have retained their configuration for the past \\~ 0.8 million years. It is unlikely that multiple blocks in the study area combined to trigger much larger shocks during this period, in contrast to adjacent regions where events with magnitudes greater than 7 have been postulated based on paleoseismic excavations.

  20. Cell boundary fault detection system

    DOEpatents

    Archer, Charles Jens; Pinnow, Kurt Walter; Ratterman, Joseph D.; Smith, Brian Edward

    2011-04-19

    An apparatus and program product determine a nodal fault along the boundary, or face, of a computing cell. Nodes on adjacent cell boundaries communicate with each other, and the communications are analyzed to determine if a node or connection is faulty.

  1. Unraveling polyphase brittle tectonics through fault-slip analysis in the Voltri Massif, Western Alps (Italy)

    NASA Astrophysics Data System (ADS)

    Federico, Laura; Crispini, Laura; Vigo, Andrea; Malatesta, Cristina; Capponi, Giovanni

    2014-05-01

    crosscutting relationships we reconstructed the following sequence of stress/strain tensors: T1: strike-slip, with NNW-SSE to NW-SE striking σ1/Z axis; T2: strike-slip (locally oblique), with E-W to NE-SW striking σ1/Z axis; T3: extensional/transtensional, with NW-SE or NE-SW striking σ3/X axis in the different fault segments. As all faults with a complete fault-slip datum have been measured in bedrock lithologies, no age constraints are available. We therefore used the results of the paleostress investigations, the orientation and kinematics of the faults and the studies in adjacent areas with dated structures to unravel the sequence of events. The T1 tensor fits the orientation of structures described by Maino et al. (Tectonics, 32, 1-27, 2013) related to a Rupelian-lower Chattian tectonic event: it is possibly linked to the far-field incipient rifting in the future Liguro-Provençal basin. The σ1/Z axis of T2 tensor fits the NE-SW shortening of Oligo-Miocene thrusts well-known in this area: the studied faults thus may belong to a left-hand strike-slip zone that accomodated the oblique component of deformation during the rotation of Corsica-Sardinia block. Late-stage extension/transtension (T3) can be referred to a Pliocene or neotectonic stage of activity of these faults. Therefore this fault system had a prolonged activity in different tectonic settings, linked to changing geodynamic constraints.

  2. Distributed Plate Boundary Deformation Across the San Andreas Fault System, Central California

    NASA Astrophysics Data System (ADS)

    Dyson, M.; Titus, S. J.; Demets, C.; Tikoff, B.

    2007-12-01

    Plate boundaries are now recognized as broad zones of complex deformation as opposed to narrow zones with discrete offsets. When assessing how plate boundary deformation is accommodated, both spatially and temporally, it is therefore crucial to understand the relative contribution of the discrete and distributed components of deformation. The creeping segment of the San Andreas fault is an ideal location to study the distribution of plate boundary deformation for several reasons. First, the geometry of the fault system in central California is relatively simple. Plate motion is dominated by slip along the relatively linear strike-slip San Andreas fault, but also includes lesser slip along the adjacent and parallel Hosgri-San Gregorio and Rinconada faults, as well as within the borderlands between the three fault strands. Second, the aseismic character of the San Andreas fault in this region allows for the application of modern geodetic techniques to assess creep rates along the fault and across the region. Third, geologic structures within the borderlands are relatively well-preserved allowing comparison between modern and ancient rates and styles of deformation. Continuous GPS stations, alignment arrays surveys, and other geodetic methods demonstrate that approximately 5 mm/yr of distributed slip is accumulated (on top of the fault slip rate) across a 70-100 km wide region centered on the San Andreas fault. New campaign GPS data also suggest 2-5 mm/yr of deformation in the borderlands. These rates depend on the magnitude of the coseismic and postseismic corrections that must be made to our GPS time series to compensate for the 2003 San Simeon and 2004 Parkfield earthquakes, which rupture faults outside, but near the edges of our GPS network. The off-fault deformation pattern can be compared to the style of permanent deformation recorded in the geologic record. Fold and thrust belts in the borderlands are better developed in the Tertiary sedimentary rocks west of

  3. Paleoseismology of the imbricate fault array in the Sierra Cucapah, northern Baja California, Mexico

    NASA Astrophysics Data System (ADS)

    Hernández, A. P.; Fletcher, J. M.; Spelz, R.; Rockwell, T. K.; Teran, O. J.

    2013-05-01

    The Mw 7.2 Mayor-Cucapah earthquake produced cascading slip along six distinct faults that extend 120 km and is regarded as the most complex surface rupture ever recorded on the Pacific North American plate margin. In general master faults do not control local topography and many are blind structures buried beneath several kilometers of sediments, suggesting the overall slip rates are very slow on this newly recognized system of faults. We have performed a detailed paleo-seismic study along the Borrego Graben, which forms a key segment of the 2010 rupture. We report the first determinations of the distribution, magnitude and recurrence intervals of the past three surface ruptures. The Borrego Valley is an asymmetric graben controlled by the east-dipping Borrego fault and here a telescopic sequence of six distinct alluvial fan surfaces that range in age to latest Pleistocene (20 ka) form important structural markers for determining cross cutting relationships and cumulative slip of the past three ruptures. In addition to systematic mapping of the fan deposits and surface ruptures, 49 topographic profiles were generated using LiDAR DEM's to document the absolute vertical displacement accumulated in multiple surface ruptures along the fault. Vertical offset ranges up to 8 m and older fan surface show systematically greater offset than adjacent younger fan surfaces. We document at least three major surface ruptures including the 2010 event and their distribution demonstrates the existence of two fault segments with contrasting rupture histories. Vertical displacement along the northern segment accumulated in the oldest and youngest 2010 surface ruptures, whereas, that on the southern segment is controlled by a rupture intermediate in age. All three events overlap for a distance of 1.5 km in the northern extreme of the southern segment and here the telescopic fan configuration observed along the length of the Borrego graben converts locally to a nested sequence with

  4. Correlation between deep fluids, tremor and creep along the central San Andreas fault.

    PubMed

    Becken, Michael; Ritter, Oliver; Bedrosian, Paul A; Weckmann, Ute

    2011-12-01

    The seismicity pattern along the San Andreas fault near Parkfield and Cholame, California, varies distinctly over a length of only fifty kilometres. Within the brittle crust, the presence of frictionally weak minerals, fault-weakening high fluid pressures and chemical weakening are considered possible causes of an anomalously weak fault northwest of Parkfield. Non-volcanic tremor from lower-crustal and upper-mantle depths is most pronounced about thirty kilometres southeast of Parkfield and is thought to be associated with high pore-fluid pressures at depth. Here we present geophysical evidence of fluids migrating into the creeping section of the San Andreas fault that seem to originate in the region of the uppermost mantle that also stimulates tremor, and evidence that along-strike variations in tremor activity and amplitude are related to strength variations in the lower crust and upper mantle. Interconnected fluids can explain a deep zone of anomalously low electrical resistivity that has been imaged by magnetotelluric data southwest of the Parkfield-Cholame segment. Near Cholame, where fluids seem to be trapped below a high-resistivity cap, tremor concentrates adjacent to the inferred fluids within a mechanically strong zone of high resistivity. By contrast, subvertical zones of low resistivity breach the entire crust near the drill hole of the San Andreas Fault Observatory at Depth, northwest of Parkfield, and imply pathways for deep fluids into the eastern fault block, coincident with a mechanically weak crust and the lower tremor amplitudes in the lower crust. Fluid influx to the fault system is consistent with hypotheses of fault-weakening high fluid pressures in the brittle crust. PMID:22129729

  5. Correlation between deep fluids, tremor and creep along the central San Andreas fault

    USGS Publications Warehouse

    Becken, M.; Ritter, O.; Bedrosian, P.A.; Weckmann, U.

    2011-01-01

    The seismicity pattern along the San Andreas fault near Parkfield and Cholame, California, varies distinctly over a length of only fifty kilometres. Within the brittle crust, the presence of frictionally weak minerals, fault-weakening high fluid pressures and chemical weakening are considered possible causes of an anomalously weak fault northwest of Parkfield. Non-volcanic tremor from lower-crustal and upper-mantle depths is most pronounced about thirty kilometres southeast of Parkfield and is thought to be associated with high pore-fluid pressures at depth. Here we present geophysical evidence of fluids migrating into the creeping section of the San Andreas fault that seem to originate in the region of the uppermost mantle that also stimulates tremor, and evidence that along-strike variations in tremor activity and amplitude are related to strength variations in the lower crust and upper mantle. Interconnected fluids can explain a deep zone of anomalously low electrical resistivity that has been imaged by magnetotelluric data southwest of the Parkfield-Cholame segment. Near Cholame, where fluids seem to be trapped below a high-resistivity cap, tremor concentrates adjacent to the inferred fluids within a mechanically strong zone of high resistivity. By contrast, subvertical zones of low resistivity breach the entire crust near the drill hole of the San Andreas Fault Observatory at Depth, northwest of Parkfield, and imply pathways for deep fluids into the eastern fault block, coincident with a mechanically weak crust and the lower tremor amplitudes in the lower crust. Fluid influx to the fault system is consistent with hypotheses of fault-weakening high fluid pressures in the brittle crust. ?? 2011 Macmillan Publishers Limited. All rights reserved.

  6. Transform Faults and Lithospheric Structure: Insights from Numerical Models and Shipboard and Geodetic Observations

    NASA Astrophysics Data System (ADS)

    Takeuchi, Christopher S.

    In this dissertation, I study the influence of transform faults on the structure and deformation of the lithosphere, using shipboard and geodetic observations as well as numerical experiments. I use marine topography, gravity, and magnetics to examine the effects of the large age-offset Andrew Bain transform fault on accretionary processes within two adjacent segments of the Southwest Indian Ridge. I infer from morphology, high gravity, and low magnetization that the extremely cold and thick lithosphere associated with the Andrew Bain strongly suppresses melt production and crustal emplacement to the west of the transform fault. These effects are counteracted by enhanced temperature and melt production near the Marion Hotspot, east of the transform fault. I use numerical models to study the development of lithospheric shear zones underneath continental transform faults (e.g. the San Andreas Fault in California), with a particular focus on thermomechanical coupling and shear heating produced by long-term fault slip. I find that these processes may give rise to long-lived localized shear zones, and that such shear zones may in part control the magnitude of stress in the lithosphere. Localized ductile shear participates in both interseismic loading and postseismic relaxation, and predictions of models including shear zones are within observational constraints provided by geodetic and surface heat flow data. I numerically investigate the effects of shear zones on three-dimensional postseismic deformation. I conclude that the presence of a thermally-activated shear zone minimally impacts postseismic deformation, and that thermomechanical coupling alone is unable to generate sufficient localization for postseismic relaxation within a ductile shear zone to kinematically resemble that by aseismic fault creep (afterslip). I find that the current record geodetic observations of postseismic deformation do not provide robust discriminating power between candidate linear and

  7. Correlation between deep fluids, tremor and creep along the central San Andreas fault.

    PubMed

    Becken, Michael; Ritter, Oliver; Bedrosian, Paul A; Weckmann, Ute

    2011-11-30

    The seismicity pattern along the San Andreas fault near Parkfield and Cholame, California, varies distinctly over a length of only fifty kilometres. Within the brittle crust, the presence of frictionally weak minerals, fault-weakening high fluid pressures and chemical weakening are considered possible causes of an anomalously weak fault northwest of Parkfield. Non-volcanic tremor from lower-crustal and upper-mantle depths is most pronounced about thirty kilometres southeast of Parkfield and is thought to be associated with high pore-fluid pressures at depth. Here we present geophysical evidence of fluids migrating into the creeping section of the San Andreas fault that seem to originate in the region of the uppermost mantle that also stimulates tremor, and evidence that along-strike variations in tremor activity and amplitude are related to strength variations in the lower crust and upper mantle. Interconnected fluids can explain a deep zone of anomalously low electrical resistivity that has been imaged by magnetotelluric data southwest of the Parkfield-Cholame segment. Near Cholame, where fluids seem to be trapped below a high-resistivity cap, tremor concentrates adjacent to the inferred fluids within a mechanically strong zone of high resistivity. By contrast, subvertical zones of low resistivity breach the entire crust near the drill hole of the San Andreas Fault Observatory at Depth, northwest of Parkfield, and imply pathways for deep fluids into the eastern fault block, coincident with a mechanically weak crust and the lower tremor amplitudes in the lower crust. Fluid influx to the fault system is consistent with hypotheses of fault-weakening high fluid pressures in the brittle crust.

  8. Archaeoseismological Study of Prehistoric Earthquakes in Anhui Province, China and Adjacent Areas

    NASA Astrophysics Data System (ADS)

    Yao, D.; Shen, X.; Gong, X.; Wu, W.; Hu, Z.; Zheng, H.; Chen, A.; Zhao, P.; Yang, Y.

    2014-12-01

    Damaging earthquakes on faults typically recur at intervals of centuries to millennia but the seismographs that record them have only been around for about hundred years. Complete records of earthquakes of Ms5 or above for Anhui Province of China and its adjacent areas began in 1336 and most previous records were lost. To reduce the hazard from earthquakes we need a longer record of them than can be provided from such instruments. Archaeoseismological evidence has the potential to determine earthquake activity over millennial time spans, especially when integrated with historical documents and geological evidence. In recent years, taking advantage of large-scale civil excavations, our research team including earthquake and archaeological scientists have cataloged, identified, and analyzed deformation relics of the late-Quaternary period, especially the Neolithic Age. Prehistoric earthquake traces were found in the cultural layers of the Western Zhou Dynasty and the Spring and Autumn Period in Southwest Anhui, the late Dawenkou cultural period in North Anhui, and the Eastern Zhou in South Henan. Along the segment of the Tanlu Fault Zone on the border of Jiangsu-Anhui Provinces, several rapid deformation events mainly in the form of oblique translational thrust had occurred since Late Pleistocene, which was confirmed by microscopic studies. The research findings have partly filled the gap of earthquake records in the area and enriched research methodologies in archaeology, prehistoric earthquakes and earthquake prediction. The project was sponsored by China Earthquake Science Special Research Funding Program (#201308012)

  9. Towards "realistic" fault zones in a 3D structure model of the Thuringian Basin, Germany

    NASA Astrophysics Data System (ADS)

    Kley, J.; Malz, A.; Donndorf, S.; Fischer, T.; Zehner, B.

    2012-04-01

    3D computer models of geological architecture are evolving into a standard tool for visualization and analysis. Such models typically comprise the bounding surfaces of stratigraphic layers and faults. Faults affect the continuity of aquifers and can themselves act as fluid conduits or barriers. This is one reason why a "realistic" representation of faults in 3D models is desirable. Still so, many existing models treat faults in a simplistic fashion, e.g. as vertical downward projections of fault traces observed at the surface. Besides being geologically and mechanically unreasonable, this also causes technical difficulties in the modelling workflow. Most natural faults are inclined and may change dips according to rock type or flatten into mechanically weak layers. Boreholes located close to a fault can therefore cross it at depth, resulting in stratigraphic control points allocated to the wrong block. Also, faults tend to split up into several branches, forming fault zones. Obtaining a more accurate representation of faults and fault zones is therefore challenging. We present work-in-progress from the Thuringian Basin in central Germany. The fault zone geometries are never fully constrained by data and must be extrapolated to depth. We use balancing of serial, parallel cross-sections to constrain subsurface extrapolations. The structure sections are checked for consistency by restoring them to an undeformed state. If this is possible without producing gaps or overlaps, the interpretation is considered valid (but not unique) for a single cross-section. Additional constraints are provided by comparison of adjacent cross-sections. Structures should change continuously from one section to another. Also, from the deformed and restored cross-sections we can measure the strain incurred during deformation. Strain should be compatible among the cross-sections: If at all, it should vary smoothly and systematically along a given fault zone. The stratigraphic contacts and

  10. THE TRUSS BRIDGE SEGMENT OF THE TRIBOROUGH BRIDGE IN FOREGROUND ...

    Library of Congress Historic Buildings Survey, Historic Engineering Record, Historic Landscapes Survey

    THE TRUSS BRIDGE SEGMENT OF THE TRIBOROUGH BRIDGE IN FOREGROUND AND THE HELL GATE BRIDGE IN THE BACKGROUND ADJACENT TO THE SUSPENSION SEGMENT OF THE TRIBOROUGH BRIDGE. - Triborough Bridge, Passing through Queens, Manhattan & the Bronx, Queens (subdivision), Queens County, NY

  11. A three-dimensional mechanical analysis of normal fault evolution and joint development in perturbed stress fields around normal faults

    NASA Astrophysics Data System (ADS)

    Kattenhorn, Simon Allen

    1998-09-01

    This thesis investigates the role of three dimensionality in the evolution of normal fault systems and joint development in perturbed stress fields induced by slipping normal faults. This is accomplished using: (1) 3D numerical models; (2) field observations of fault and joint characteristics; and (3) seismic data interpretations of 3D normal fault geometries. Numerical models that incorporate the contribution of an increasing lithostatic load with increasing depth on fault slip behavior indicate that normal faults are more prone to slip near the top than the bottom. Energy release rates are maximized at the upper tip, suggesting that faults should grow preferentially in an up-dip direction. For the case of laterally segmented faults, mechanical interaction promotes propagation of segments towards each other, which may result in composite fault surfaces that are longer than they are tall, in agreement with documented natural examples. Slipping faults perturb the surrounding stress field. Field relationships in Arches National Park, Utah, suggest that joints grew in the perturbed stress field around the faults. Numerical analyses indicate that joint orientations depend on the location along the fault tipline in 3D, and may range from fault-parallel to fault-perpendicular. In addition, as the ratio of fault-parallel to fault-perpendicular remote stress increases, so too does the distance away from the fault affected by the perturbed field. In relay zones, joints forming at high angles to fault strike are likely to continue propagating away from the fault if the fault-parallel stress approaches, or slightly exceeds, the fault-perpendicular remote stress during fault slip. Multiple slip maxima at the same stratigraphic level on apparently continuous fault surfaces in 3D seismic data attest to initial lateral segmentation. Mechanical interaction and lateral propagation led to linkage of fault segments and the formation of composite faults that are longer than they are

  12. Splay fault surface rupture triggered by the 2010 Chile earthquake

    NASA Astrophysics Data System (ADS)

    Melnick, D.; Moreno, M.; Motagh, M.; Cisternas, M.

    2010-12-01

    Faults that splay from megathrusts have been imaged at several active plate boundaries and observed on exposed fossil sections. Due to their steep dip, slip along such structures triggered by a megathrust earthquake may enhance near-field tsunami waves and shorten arrival times. However, motion of splay faults and their role on seismotectonic segmentation has remained elusive due to their predominant offshore location and few historical accounts. Though splay fault slip has been inferred during the 2004 Sumatra and other events, surface ruptures triggered by the 1964 M9.2 Alaska earthquake have been the only documented so far. Here we use field, geodetic and InSAR data to document surface fault rupture and coastal tilting at Isla Santa Maria (ISM; 37S) during the M8.8 earthquake of February 27, 2010. We integrate the observed deformation with previous knowledge of the regional structure to propose triggering of a splay fault. ISM is 75 km inland from the trench, at the intersection of the Arauco Bay and Santa María fault systems (SMFS), both consisting of blind reverse faults that propagate folds. The SMFS is associated to a cluster of microseismicity extending from the plate interface at 15 km to 2 km depth. An offshore seismic reflection profile across this cluster images a main reverse fault with a flat-ramp-flat structure shortcutting to the footwall. The 2010 surface breaks extend across the entire northern part of the island for 900 m, divided in two domains of ENE-WSW oriented structures separated by an E-W striking transfer zone. Each domain consists of faults and fractures with en echelon patterns, with a maximum normal vertical displacement of 80 cm. The geometry of surface ruptures is consistent with dextral transtensional kinematics. We associate the surface breaks to transpressional growth of the fault-cored anticline northeast of ISM; transtension at the surface relates to fold bending. Surface rupture was accompanied by 1.6-2.2 m of coastal uplift

  13. Cervical facet dislocation adjacent to the fused motion segment.

    PubMed

    Yokoyama, Kunio; Kawanishi, Masahiro; Yamada, Makoto; Tanaka, Hidekazu; Ito, Yutaka; Kuroiwa, Toshihiko

    2016-01-01

    This study reports on a case that forces re-examination of merits and demerits of anterior cervical fusion. A 79-year-old male was brought to the emergency room (ER) of our hospital after he fell and struck the occipital region of his head following excessive alcohol consumption. Four years prior, he had undergone anterior cervical discectomy and fusion of C5/6 and a magnetic resonance imaging (MRI) performed 3 years after this surgery indicated that he was suffering from degeneration of C6/7 intervertebral discs. After arriving at the ER, he presented motor impairment at level C7 and lower of manual muscle testing grade 1 as well as moderate loss of physical sensation from the trunk and peripheries of both upper limbs to the peripheries of both lower limbs (Frankel B). Cervical computed tomography (CT) indicated anterior dislocation of C6/7, and MRI indicated severe spinal cord edema. We performed manipulative reduction of C6/7 with the patient under general anesthesia. Next, we performed laminectomy on C5-T1 and posterior fusion on C6/7. Postoperative CT indicated that cervical alignment had improved, and MRI indicated that the spinal cord edema observed prior to surgery had been mitigated. Three months after surgery, motor function and sensory impairment of the lower limbs had improved, and the patient was ambulatory upon discharge from the hospital (Frankel D). In the present case, although C5 and 6 were rigidly fused, degeneration of the C6/7 intervertebral disc occurred and stability was compromised. As a result, even slight trauma placed a severe dynamic burden on the facet joint of C6/7, which led to dislocation.

  14. Fault-related clay authigenesis along the Moab Fault: Implications for calculations of fault rock composition and mechanical and hydrologic fault zone properties

    USGS Publications Warehouse

    Solum, J.G.; Davatzes, N.C.; Lockner, D.A.

    2010-01-01

    The presence of clays in fault rocks influences both the mechanical and hydrologic properties of clay-bearing faults, and therefore it is critical to understand the origin of clays in fault rocks and their distributions is of great importance for defining fundamental properties of faults in the shallow crust. Field mapping shows that layers of clay gouge and shale smear are common along the Moab Fault, from exposures with throws ranging from 10 to ???1000 m. Elemental analyses of four locations along the Moab Fault show that fault rocks are enriched in clays at R191 and Bartlett Wash, but that this clay enrichment occurred at different times and was associated with different fluids. Fault rocks at Corral and Courthouse Canyons show little difference in elemental composition from adjacent protolith, suggesting that formation of fault rocks at those locations is governed by mechanical processes. Friction tests show that these authigenic clays result in fault zone weakening, and potentially influence the style of failure along the fault (seismogenic vs. aseismic) and potentially influence the amount of fluid loss associated with coseismic dilation. Scanning electron microscopy shows that authigenesis promotes that continuity of slip surfaces, thereby enhancing seal capacity. The occurrence of the authigenesis, and its influence on the sealing properties of faults, highlights the importance of determining the processes that control this phenomenon. ?? 2010 Elsevier Ltd.

  15. Fault-related clay authigenesis along the Moab Fault: Implications for calculations of fault rock composition and mechanical and hydrologic fault zone properties

    NASA Astrophysics Data System (ADS)

    Solum, John G.; Davatzes, Nicholas C.; Lockner, David A.

    2010-12-01

    The presence of clays in fault rocks influences both the mechanical and hydrologic properties of clay-bearing faults, and therefore it is critical to understand the origin of clays in fault rocks and their distributions is of great importance for defining fundamental properties of faults in the shallow crust. Field mapping shows that layers of clay gouge and shale smear are common along the Moab Fault, from exposures with throws ranging from 10 to ˜1000 m. Elemental analyses of four locations along the Moab Fault show that fault rocks are enriched in clays at R191 and Bartlett Wash, but that this clay enrichment occurred at different times and was associated with different fluids. Fault rocks at Corral and Courthouse Canyons show little difference in elemental composition from adjacent protolith, suggesting that formation of fault rocks at those locations is governed by mechanical processes. Friction tests show that these authigenic clays result in fault zone weakening, and potentially influence the style of failure along the fault (seismogenic vs. aseismic) and potentially influence the amount of fluid loss associated with coseismic dilation. Scanning electron microscopy shows that authigenesis promotes that continuity of slip surfaces, thereby enhancing seal capacity. The occurrence of the authigenesis, and its influence on the sealing properties of faults, highlights the importance of determining the processes that control this phenomenon.

  16. A “mesh” of crossing faults: Fault networks of southern California

    NASA Astrophysics Data System (ADS)

    Janecke, S. U.

    2009-12-01

    hypocenters) that the master dextral faults zones pass beneath shallower crossing fault arrays above them and this mechanism may transfer strain through the blocking zones. 3) The curvature of strands of the Coyote Creek fault and the Elsinore fault are similar along their SE 60 km. The scale, locations and concavity of bends are so similar that their shape appears to be coordinated. The matching contractional and extensional bends suggests that originally straighter dextral fault zones may be deforming in response of coeval sinistral deformation between, beneath, and around them. 4) Deformation is strongly domainal with one style or geometry of structure dominating in one area then another in an adjacent area. Boundaries may be abrupt. 5) There are drastic lateral changes in the width of damage zones adjacent to master faults. Outlines of the deformation related to some dextral fault zones resemble a snake that has ingested a squirming cat or soccer ball. 6) A mesh of interconnected faults seems to transfer slip back and forth between structures. 7) Scarps are not necessarily more abundant on the long master faults than on connector or crossing faults. Much remains to be learned upon completion the fault map.

  17. Identification of a major segment boundary between two megathrust subduction zone earthquakes from aftershock seismicity

    NASA Astrophysics Data System (ADS)

    Sobiesiak, M.; Victor, P.; Eggert, S.

    2009-04-01

    Aftershock seismicity is commonly used to characterize the extent of rupture planes of megathrust earthquakes. From unique datasets, covering the two adjacent fault planes of the Mw 8.0, 1995, Antofagasta and the Mw 7.7, 2007, Tocopilla earthquakes, we were able to identify a segment boundary (SB), located beneath Mejillones Peninsula. This segment boundary hosted the onset of the Antofagasta rupture and constituted the end of the Tocopilla rupture plane. The data recorded during the mission of the German Task Force for Earthquakes after the 2007 Tocopilla earthquake is supporting our observations regarding the northern part of the SB. 34 seismological stations registered the aftershocks from November 2007 until May 2008. First hypocenter determinations show that the aftershock sequences of both events meet along this E-W oriented segment boundary. The segment boundary is furthermore conformed by the historic record of megathrust events. Evidence for long term persistency of this SB comes from geological observations as differential uplift rates across the boundary and different fault patterns. Geomorpholocical analysis defines a topographic anomaly ~ 20 km wide and oriented along strike the SB..The main shock hypocenter determinations (NEIC, local network, ISC) which are related to the start of the rupture are all located in this zone. The SB is further characterized by intermediate b-values derived from a spatial b-value study of the Antofagasta fault plane and hosts several elongated clusters of aftershock seismicity. A detailed study of the focal mechanism solutions in one of these clusters showed a number of aligned strike slip events with one E-W striking nodal plane having a strike angle which is similar to the angle of subduction obliquity of the oceanic Nazca plate in this area. In further investigations we will search for detailed information on the nature and dynamics of processes along such a segment boundary, their meaning for the initiation of large

  18. Mechanical controls on the spatial and temporal variability of faulting mechanisms in sandstone along the Moab normal fault, Utah

    NASA Astrophysics Data System (ADS)

    Davatzes, N. C.; Aydin, A.

    2003-12-01

    Segmentation is a fundamental characteristic of faults. However, the effect of segmentation on the process of fault development, the architecture of the fault zone, and the properties of faults are poorly understood. Along the Moab fault, a basin scale normal fault with ~1 km of throw in SE Utah, segmentation is associated with localized changes in the density and types of structures associated with faulting in sandstone. Changes in the types of structural elements are associated with fault development by two different mechanisms in sandstone: (1) cataclastic shear failure that produces deformation bands and (2) the repeated formation and subsequent shearing of joints that leads to the formation of a brecciated fault zone. Deformation bands are prevalent along the entire length of the fault system and band density is greatest within relays between normal fault segments that are subjected to a component of strike-parallel contraction. The joints and sheared joints only occur at intersections between normal fault segments and relays that are subjected to strike-parallel extension where they overprint deformation bands. We contend that spatial variation of the faulting mechanisms in sandstone is associated with the stress perturbation around the fault. We used the geometry and kinematics of the fault segments and an estimated burial depth of 2 km to simulate the mechanical behavior of the fault system in linear elastic boundary element models using Poly3D. We looked specifically for changes in the stress state that would cause a transition from deformation band formation to joint formation because joints are the youngest structural elements wherever they occur. Joints form normal to the least compressive principal stress when this stress exceeds the tensile strength of the rock. We also note that cataclasis in deformation bands represent a loss of volume, whereas jointing and breccia formation are dilatant processes. Consequently the mean stress can act as an

  19. Diachronous fault array growth within continental rift basins: Quantitative analyses from the East Shetland Basin, northern North Sea

    NASA Astrophysics Data System (ADS)

    Claringbould, Johan; Bell, Rebecca; Jackson, Christopher; Gawthorpe, Robert; Odinsen, Tore

    2016-04-01

    The evolution of rift basins has been the subject of many studies, however, these studies have been mainly restricted to investigating the geometry of rift-related fault arrays. The relative timing of development of individual faults that make up the fault array is not yet well constrained. First-order tectono-stratigraphic models for rifts predict that normal faults develop broadly synchronously throughout the basin during a temporally distinct 'syn-rift' episode. However, largely due to the mechanical interaction between adjacent structures, distinctly diachronous activity is known to occur on the scale of individual fault segments and systems. Our limited understanding of how individual segments and systems contribute to array-scale strain largely reflects the limited dimension and resolution of the data available and methods applied. Here we utilize a regional extensive subsurface dataset comprising multiple 3D seismic MegaSurveys (10,000 km2), long (>75km) 2D seismic profiles, and exploration wells, to investigate the evolution of the fault array in the East Shetland Basin, North Viking Graben, northern North Sea. Previous studies propose this basin formed in response to multiphase rifting during two temporally distinct extensional phases in the Permian-Triassic and Middle-to-Late Jurassic, separated by a period of tectonic quiescence and thermal subsidence in the Early Jurassic. We document the timing of growth of individual structures within the rift-related fault array across the East Shetland Basin, constraining the progressive migration of strain from pre-Triassic-to-Late Jurassic. The methods used include (i) qualitative isochron map analysis, (ii) quantitative syn-kinematic deposit thickness difference across fault & expansion index calculations, and (iii) along fault throw-depth & backstripped displacement-length analyses. In contrast to established models, we demonstrate that the initiation, growth, and cessation of individual fault segments and

  20. Strain localization versus distributed deformation along strike-slip faults in eastern Tibet (Invited)

    NASA Astrophysics Data System (ADS)

    Kirby, E.; Harkins, N. W.

    2010-12-01

    Thirty-five years after the recognition of the tectonic significance of Eurasian strike-slip faults, the mechanical implications of these structures and how they accommodate ongoing Indo-Asian convergence continues to engender vigorous debate. Do the rules of plate tectonics, where strike-slip faults bound quasi-rigid blocks, govern intracontinental deformation? Or does strain localization simply occur along pre-existing heterogeneities in an otherwise continuously medium? Despite improved estimates of slip-rates along nearly all of the major fault systems over the past decade, we have not yet reached consensus on these questions. One possible reason is that most studies have been focused along portions of these fault systems adjacent to rigid blocks, where slip-rates are expected to be relatively high and spatially uniform, irrespective of mechanical behavior. In these regions, slip-rates alone may not be sufficient to distinguish between competing modes of deformation. In contrast, where these major fault systems are embedded within deforming regions, slip-rates, and how they vary along strike, may yield insight into the relationship between fault-slip and deformation of the surrounding crust. Within the Indo-Asian collision zone, such conditions exist in several places: at the eastern and western terminations of the Kunlun fault, along the western segments of the Yushu-Ganzi-Xianshuihe fault, and perhaps along much of the Karakorum fault. Here, we focus on recent results along the eastern Kunlun fault. In the region east of the Qaidam Basin, the Kunlun fault transects high topography in the Anyemaqen Shan for ~250 km along strike. Late Quaternary slip-rates determined at 9 localities reveal a systematic decrease along this section of the fault, from >10 mm/yr to <2 mm/yr, a result corroborated by existing geodetic data. Moreover, the high relief within the Anyemaqen Shan appears to reflect internal deformation of a broad region surrounding the fault tip

  1. 1. OVERVIEW SHOWING FIRING CONTROL BLOCKHOUSE 0502 AND ADJACENT OBSERVATION ...

    Library of Congress Historic Buildings Survey, Historic Engineering Record, Historic Landscapes Survey

    1. OVERVIEW SHOWING FIRING CONTROL BLOCKHOUSE 0502 AND ADJACENT OBSERVATION TOWER. WATER BRAKE TROUGH SEGMENT AT LOWER RIGHT. Looking north northeast. - Edwards Air Force Base, South Base Sled Track, Firing & Control Blockhouse for 10,000-foot Track, South of Sled Track at midpoint of 20,000-foot track, Lancaster, Los Angeles County, CA

  2. Fault diagnosis

    NASA Technical Reports Server (NTRS)

    Abbott, Kathy

    1990-01-01

    The objective of the research in this area of fault management is to develop and implement a decision aiding concept for diagnosing faults, especially faults which are difficult for pilots to identify, and to develop methods for presenting the diagnosis information to the flight crew in a timely and comprehensible manner. The requirements for the diagnosis concept were identified by interviewing pilots, analyzing actual incident and accident cases, and examining psychology literature on how humans perform diagnosis. The diagnosis decision aiding concept developed based on those requirements takes abnormal sensor readings as input, as identified by a fault monitor. Based on these abnormal sensor readings, the diagnosis concept identifies the cause or source of the fault and all components affected by the fault. This concept was implemented for diagnosis of aircraft propulsion and hydraulic subsystems in a computer program called Draphys (Diagnostic Reasoning About Physical Systems). Draphys is unique in two important ways. First, it uses models of both functional and physical relationships in the subsystems. Using both models enables the diagnostic reasoning to identify the fault propagation as the faulted system continues to operate, and to diagnose physical damage. Draphys also reasons about behavior of the faulted system over time, to eliminate possibilities as more information becomes available, and to update the system status as more components are affected by the fault. The crew interface research is examining display issues associated with presenting diagnosis information to the flight crew. One study examined issues for presenting system status information. One lesson learned from that study was that pilots found fault situations to be more complex if they involved multiple subsystems. Another was pilots could identify the faulted systems more quickly if the system status was presented in pictorial or text format. Another study is currently under way to

  3. Fault and anthropogenic processes in central California constrained by satellite and airborne InSAR and in-situ observations

    NASA Astrophysics Data System (ADS)

    Liu, Zhen; Lundgren, Paul

    2016-07-01

    The San Andreas Fault (SAF) system is the primary plate boundary in California, with the central SAF (CSAF) lying adjacent to the San Joaquin Valley (SJV), a vast structural trough that accounts for about one-sixth of the United Sates' irrigated land and one-fifth of its extracted groundwater. The CSAF displays a range of fault slip behavior with creeping in its central segment that decreases towards its northwest and southeast ends, where the fault transitions to being fully locked. At least six Mw ~6.0 events since 1857 have occurred near the Parkfield transition, most recently in 2004. Large earthquakes also occurred on secondary faults parallel to the SAF, the result of distributed deformation across the plate boundary zone. Recent studies have revealed the complex interaction between anthropogenic related groundwater depletion and the seismic activity on adjacent faults through stress interaction. Despite recent progress, many questions regarding fault and anthropogenic processes in the region still remain. For example, how is the relative plate motion accommodated between the CSAF and off-fault deformation? What is the distribution of fault creep and slip deficit at shallow depths? What are the spatiotemporal variations of fault slip? What are the spatiotemporal characteristics of anthropogenic and lithospheric processes and how do they interact with each other? To address these, we combine satellite InSAR and NASA airborne UAVSAR data to image on and off-fault deformation. The UAVSAR data cover fault perpendicular swaths imaged from opposing look directions and fault parallel swaths since 2009. The much finer spatial resolution and optimized viewing geometry provide important constraints on near fault deformation and fault slip at very shallow depth. We performed a synoptic InSAR time series analysis using ERS-1/2, Envisat, ALOS and UAVSAR interferograms. The combined C-band ERS-1/2 and Envisat data provide a long time interval of SAR data over the region

  4. Predictive Upper Cretaceous to Early Miocene Paleogeography of the San Andreas Fault System

    NASA Astrophysics Data System (ADS)

    Burnham, K.

    2006-12-01

    Paleogeographic reconstruction of the region of the San Andreas fault was hampered for more than twenty years by the apparent incompatibility of authoritative lithologic correlations. These led to disparate estimates of dextral strike-slip offsets, notably 315 km between Pinnacles and Neenach Volcanics (Matthews, 1976), versus 563 km between Anchor Bay and Eagle Rest Peak (Ross et al., 1973). In addition, estimates of total dextral slip on the San Gregorio fault have ranged from 5 km to 185 km. Sixteen upper Cretaceous and Paleogene conglomerates of the California Coast Ranges, from Anchor Bay to Simi Valley, have been included in a multidisciplinary study. Detailed analysis, including microscopic petrography and microprobe geochemistry, verified Seiders and Cox's (1992) and Wentworth's (1996) correlation of the upper Cretaceous Strata of Anchor Bay with an unnamed conglomerate east of Half Moon Bay. Similar detailed study, with the addition of SHRIMP U/Pb zircon dating, verified that the Paleocene or Eocene Point Reyes Conglomerate at Point Reyes is a tectonically displaced segment of the Carmelo Formation of Point Lobos. These studies centered on identification of matching unique clast varieties, rather than on simply counting general clast types, and included analyses of matrices, fossils, paleocurrents, diagenesis, adjacent rocks, and stratigraphy. The work also led to three new correlations: the Point Reyes Conglomerate with granitic source rock at Point Lobos; a magnetic anomaly at Black Point with a magnetic anomaly near San Gregorio; and the Strata of Anchor Bay with previously established source rock, the potassium-poor Logan Gabbro (Ross et al., 1973) at a more recently recognized location (Brabb and Hanna, 1981; McLaughlin et al., 1996) just east of the San Gregorio fault, south of San Gregorio. From these correlations, an upper Cretaceous early Oligocene paleogeography of the San Andreas fault system was constructed that honors both the Anchor Bay

  5. A hybrid hard- and soft-linked fault model for the development of Australian extensional basin systems: Reconciling observations from seismic, aeromagnetic and analogue modelling data

    SciTech Connect

    O'Brien, G.W.; Symonds, P.; Blevin, J. ); Higgins, R.

    1996-01-01

    A series of rift models has been developed for basin systems around Australia, via the interpretation of newly acquired deep crustal seismic and high resolution aeromagnetic data. These models, which incorporate observations on rift architecture, fault geometries, fault orientation, basement fabric/grain, extensional transport direction and reactivation history, have then been iteratively tested by over twenty-five sophisticated analogue modelling experiments. This work has led to the development of a hybrid hard-linked/soft-linked fault model for the Australian margin. In this model, basement grain is the principal control on the rift architecture that develops, with pre-existing fractures acting to establish discrete offsets (hard-linkages) between adjacent extensional faults and rift segments. It is these basement features which produce the rectilinear features which are so common on aeromagnetic data around the Australian margin. With progressively greater extension, the basement-involved, hard-linked system exerts virtually no influence over the type or intensity of faulting within the syn-rift phase, though they do control the fault location. Syn-rift faulting is dominated by [open quotes]soft-linked[close quotes] fault systems, with relay ramps/zones accommodating jumps in the position of the basin margin faults. During basin reactivation (particularly inversion), it is the location and geometry of the underpinning, hard-linked basement features which ultimately control the locations of the traps that develop in the syn- and post-rift section, whereas it is the soft-linked fault system which is the primary control on the fluid migration pathways. Reconciling these concepts provides a set of powerful predictive tools for exploring both frontier and mature basins.

  6. A hybrid hard- and soft-linked fault model for the development of Australian extensional basin systems: Reconciling observations from seismic, aeromagnetic and analogue modelling data

    SciTech Connect

    O`Brien, G.W.; Symonds, P.; Blevin, J.; Higgins, R.

    1996-12-31

    A series of rift models has been developed for basin systems around Australia, via the interpretation of newly acquired deep crustal seismic and high resolution aeromagnetic data. These models, which incorporate observations on rift architecture, fault geometries, fault orientation, basement fabric/grain, extensional transport direction and reactivation history, have then been iteratively tested by over twenty-five sophisticated analogue modelling experiments. This work has led to the development of a hybrid hard-linked/soft-linked fault model for the Australian margin. In this model, basement grain is the principal control on the rift architecture that develops, with pre-existing fractures acting to establish discrete offsets (hard-linkages) between adjacent extensional faults and rift segments. It is these basement features which produce the rectilinear features which are so common on aeromagnetic data around the Australian margin. With progressively greater extension, the basement-involved, hard-linked system exerts virtually no influence over the type or intensity of faulting within the syn-rift phase, though they do control the fault location. Syn-rift faulting is dominated by {open_quotes}soft-linked{close_quotes} fault systems, with relay ramps/zones accommodating jumps in the position of the basin margin faults. During basin reactivation (particularly inversion), it is the location and geometry of the underpinning, hard-linked basement features which ultimately control the locations of the traps that develop in the syn- and post-rift section, whereas it is the soft-linked fault system which is the primary control on the fluid migration pathways. Reconciling these concepts provides a set of powerful predictive tools for exploring both frontier and mature basins.

  7. Fault mechanics

    SciTech Connect

    Segall, P. )

    1991-01-01

    Recent observational, experimental, and theoretical modeling studies of fault mechanics are discussed in a critical review of U.S. research from the period 1987-1990. Topics examined include interseismic strain accumulation, coseismic deformation, postseismic deformation, and the earthquake cycle; long-term deformation; fault friction and the instability mechanism; pore pressure and normal stress effects; instability models; strain measurements prior to earthquakes; stochastic modeling of earthquakes; and deep-focus earthquakes. Maps, graphs, and a comprehensive bibliography are provided. 220 refs.

  8. Vibration damping for the Segmented Mirror Telescope

    NASA Astrophysics Data System (ADS)

    Maly, Joseph R.; Yingling, Adam J.; Griffin, Steven F.; Agrawal, Brij N.; Cobb, Richard G.; Chambers, Trevor S.

    2012-09-01

    The Segmented Mirror Telescope (SMT) at the Naval Postgraduate School (NPS) in Monterey is a next-generation deployable telescope, featuring a 3-meter 6-segment primary mirror and advanced wavefront sensing and correction capabilities. In its stowed configuration, the SMT primary mirror segments collapse into a small volume; once on location, these segments open to the full 3-meter diameter. The segments must be very accurately aligned after deployment and the segment surfaces are actively controlled using numerous small, embedded actuators. The SMT employs a passive damping system to complement the actuators and mitigate the effects of low-frequency (<40 Hz) vibration modes of the primary mirror segments. Each of the six segments has three or more modes in this bandwidth, and resonant vibration excited by acoustics or small disturbances on the structure can result in phase mismatches between adjacent segments thereby degrading image quality. The damping system consists of two tuned mass dampers (TMDs) for each of the mirror segments. An adjustable TMD with passive magnetic damping was selected to minimize sensitivity to changes in temperature; both frequency and damping characteristics can be tuned for optimal vibration mitigation. Modal testing was performed with a laser vibrometry system to characterize the SMT segments with and without the TMDs. Objectives of this test were to determine operating deflection shapes of the mirror and to quantify segment edge displacements; relative alignment of λ/4 or better was desired. The TMDs attenuated the vibration amplitudes by 80% and reduced adjacent segment phase mismatches to acceptable levels.

  9. Evolution of faults in sandstone and their permeability

    SciTech Connect

    Antonellini, M.; Du, Yijun; Aydin, At.; Pollard, D.D. )

    1992-01-01

    In many porous sandstones world over, major fault types initiate and propagate as localized bands of deformation. Individual bands have shear displacements up to a few cm, and compaction perpendicular to the bands. Although the initiation and propagation of faults are problematic, the authors here propose that the maximum distortional strain energy density (D-criterion) can be used successfully to simulate a band fault propagation as well as the interaction and linkage of the adjacent segments. Deformation bands tend to localize into zones that have distinct patterns repeating in a broad range of scale. Some zones are associated with slip surfaces that mark the loss of cohesion between two surfaces. The authors demonstrate the particulars of individual zones and slip surfaces including their patterns and distribution for several well-known sandstones in extensional and compressional settings within Colorado Plateau. They investigate also the relationship between mappable fault patterns and the geometry and kinematics of a major detachment at Cache Valley in Arches National Park, southeastern Utah, using a Discrete Element Model. Zones of bands have permeabilities 3 to 5 order of magnitude smaller than that of parent rocks making them highly effective barriers against fluid flow. In contrast, slip surfaces are likely to be conduits with high permeability along the surface. In light of the fact that a majority of energy resources are in sandstones and that the structures described above occur also in unconsolidated sediments as potential aquifers and contamination sites, these structures and their geometries as well as the deformation processes responsible for their formation have significant implications for societal problems.

  10. Seismicity and fault geometry of the San Andreas fault around Parkfield, California and their implications

    NASA Astrophysics Data System (ADS)

    Kim, Woohan; Hong, Tae-Kyung; Lee, Junhyung; Taira, Taka'aki

    2016-05-01

    Fault geometry is a consequence of tectonic evolution, and it provides important information on potential seismic hazards. We investigated fault geometry and its properties in Parkfield, California on the basis of local seismicity and seismic velocity residuals refined by an adaptive-velocity hypocentral-parameter inversion method. The station correction terms from the hypocentral-parameter inversion present characteristic seismic velocity changes around the fault, suggesting low seismic velocities in the region east of the fault and high seismic velocities in the region to the west. Large seismic velocity anomalies are observed at shallow depths along the whole fault zone. At depths of 3-8 km, seismic velocity anomalies are small in the central fault zone, but are large in the northern and southern fault zones. At depths > 8 km, low seismic velocities are observed in the northern fault zone. High seismicity is observed in the Southwest Fracture Zone, which has developed beside the creeping segment of the San Andreas fault. The vertical distribution of seismicity suggests that the fault has spiral geometry, dipping NE in the northern region, nearly vertical in the central region, and SW in the southern region. The rapid twisting of the fault plane occurs in a short distance of approximately 50 km. The seismic velocity anomalies and fault geometry suggest location-dependent piecewise faulting, which may cause the periodic M6 events in the Parkfield region.

  11. BEHAVIOR OF THE NORTH ANATOLIAN FAULT, TURKEY, INSIGHTS FROM AN INTEGRATED PALEOSEISMIC DATASET

    NASA Astrophysics Data System (ADS)

    Fraser, J. G.; Vanneste, K.; Hubert-Ferrari, A.

    2009-12-01

    The North Anatolian Fault (NAF) is a right-lateral strike-slip plate boundary fault that arcs across northern Turkey for ~1500km. Almost the entire fault progressively ruptured in the 20th century, its cascading style indicating that stress from one fault rupture triggers fault rupture of adjacent segments. Using published, and soon to be published, paleoseismic investigations this study integrates all of the existing information about the timing of earthquakes on the NAF using a standardised procedure. Paleoseismic investigation data is compiled into a database and by taking into account uncertainties we determine the timing of paleoearthquakes. The timing data, when considered in a spatial context, reveals the temporal pattern of surface-rupturing seismicity over the last few thousand years, within the limitations of uncertainty. Based on our observations the migrating 20th century sequence of earthquakes may have occurred in the past, but probably does not occur during every seismic cycle. Based on our interpretation, the clearest pattern in the earthquake timing model is, three types of fault behaviour that correspond to the tectonic provinces within the Anatolian plate. By relating the expected fault-normal stress variation between the 3 tectonic provinces, in terms of Mohr-Coulomb failure criterion (which relates normal and shear stresses), we explain the differences in fault behavior along the NAF. The Anatolian plate drifts west at around 21mm/yr and in doing so elastic strain is stored along the NAF creating, and over time accumulating, shear stress on the fault plane. But because the fault-normal stress is not constant along the fault, it causes different patterns of seismicity. In the west, shear stress along the NAF interplays with the tensile stress associated with the Aegean extensional province; we call this the western transtensional section of the NAF. The lower normal stress means that less shear stress is required to cause fault rupture

  12. Geometry and earthquake potential of the shoreline fault, central California

    USGS Publications Warehouse

    Hardebeck, Jeanne L.

    2013-01-01

    The Shoreline fault is a vertical strike‐slip fault running along the coastline near San Luis Obispo, California. Much is unknown about the Shoreline fault, including its slip rate and the details of its geometry. Here, I study the geometry of the Shoreline fault at seismogenic depth, as well as the adjacent section of the offshore Hosgri fault, using seismicity relocations and earthquake focal mechanisms. The Optimal Anisotropic Dynamic Clustering (OADC) algorithm (Ouillon et al., 2008) is used to objectively identify the simplest planar fault geometry that fits all of the earthquakes to within their location uncertainty. The OADC results show that the Shoreline fault is a single continuous structure that connects to the Hosgri fault. Discontinuities smaller than about 1 km may be undetected, but would be too small to be barriers to earthquake rupture. The Hosgri fault dips steeply to the east, while the Shoreline fault is essentially vertical, so the Hosgri fault dips towards and under the Shoreline fault as the two faults approach their intersection. The focal mechanisms generally agree with pure right‐lateral strike‐slip on the OADC planes, but suggest a non‐planar Hosgri fault or another structure underlying the northern Shoreline fault. The Shoreline fault most likely transfers strike‐slip motion between the Hosgri fault and other faults of the Pacific–North America plate boundary system to the east. A hypothetical earthquake rupturing the entire known length of the Shoreline fault would have a moment magnitude of 6.4–6.8. A hypothetical earthquake rupturing the Shoreline fault and the section of the Hosgri fault north of the Hosgri–Shoreline junction would have a moment magnitude of 7.2–7.5.

  13. Imaging the structural style of an active normal fault through multidisciplinary geophysical investigation: a case study from the Mw 6.1, 2009 L'Aquila earthquake region (central Italy)

    NASA Astrophysics Data System (ADS)

    Villani, Fabio; Pucci, Stefano; Civico, Riccardo; De Martini, Paolo Marco; Nicolosi, Iacopo; D'Ajello Caracciolo, Francesca; Carluccio, Roberto; Di Giulio, Giuseppe; Vassallo, Maurizio; Smedile, Alessandra; Pantosti, Daniela

    2015-03-01

    The normal fault-system responsible of the 2009 Mw 6.1 L'Aquila earthquake (Paganica-San Demetrio fault-system) comprises several narrow, fault-parallel valleys of controversial origin. We investigated a key section of the southeastern portion of this fault network along the small Verupola Valley. In order to characterize its nature and possible tectonic activity, we applied multiple-geosciences techniques able to image at depth the structure associated to this peculiar landform. We integrated magnetometry, 2-D P wave and resistivity tomography, surface waves and seismic noise analysis coupled with field mapping, shallow boreholes and trenching. According to our results, the Verupola Valley is a ˜30-40-m-deep graben controlled by a SW-dipping master fault and synthetic splays paired with an antithetic NE-dipping fault. The SW-dipping splays are active and cut very shallow (<2 m deep) Late Pleistocene sediments. The small amount of cumulated vertical offset (˜15 m) across the conjugated system may indicate a young fault inception or very low Quaternary slip-rates. Due to its structural continuity with the adjacent mapped strands of the Paganica-San Demetrio fault network, we relate the Verupola Valley to the recent activity of the southeastern segment of this fault system. We also suggest that other fault-parallel valleys can have the same tectonic origin and setting of the Verupola Valley. This latter represents a scale-independent analogue from metric scale (exposed in the palaeoseismological trenches) to the Middle Aterno Basin scale (seen from seismic profiles and fault mapping). Overall, the imaged structural style is coherent with the regional tectonic setting due to Quaternary crustal extension.

  14. Fault models

    NASA Astrophysics Data System (ADS)

    Sayah, H. R.; Buehler, M. G.

    1985-06-01

    A major problem in the qualification of integrated circuit cells and in the development of adequate tests for the circuits is to lack of information on the nature and density of fault models. Some of this information is being obtained from the test structures. In particular, the Pinhole Array Capacitor is providing values for the resistance of gate oxide shorts, and the Addressable Inverter Matrix is providing values for parameter distributions such as noise margins. Another CMOS fault mode, that of the open-gated transistor, is examined and the state of the transistors assessed. Preliminary results are described for a number of open-gated structures such as transistors, inverters, and NAND gates. Resistor faults are applied to various CMOS gates and the time responses are noted. The critical value for the resistive short to upset the gate response was determined.

  15. Hayward Fault: A 50-km-long Locked Patch Regulates Its Large Earthquake Cycle (Invited)

    NASA Astrophysics Data System (ADS)

    Lienkaemper, J. J.; Simpson, R. W.; Williams, P. L.; McFarland, F. S.; Caskey, S. J.

    2010-12-01

    has a lower failure threshold on a smaller locked area. A preliminary record of north-coast SAF paleoearthquakes at the Vedanta site indicates ruptures there are probably less frequent than on the HS and any possible synchrony between these segments is presently undetectable within the uncertainties. The more proximal peninsula segment of the SAF lacks any paleoearthquake record. Occurrence of large earthquakes on adjacent faults, such as the HS and SAF can cause modest retardation of net stress accumulation and thus of time to failure by several years to a few decades, as calibrated by effects of the 1989, Mw6.9 Loma Prieta earthquake and Mw7.8,1906 earthquake on Hayward fault creep rates. The regular HS failure process appears to be dominated by a single large locked patch, tending to limit its seismic moment release to regular Mw~6.8 earthquakes. Preliminary and possibly incomplete results for other regional faults, presently appear to indicate less regularity .

  16. 3D fault drag characterization: an import tool in a fault description

    NASA Astrophysics Data System (ADS)

    Spahić, Darko; Exner, Ulrike; Grasemann, Bernhard

    2010-05-01

    Using an industrial 3D seismic dataset from the central part of the Vienna Basin (Austria), we investigate marker horizons in the hanging wall and footwall of a large-scale normal fault. The throw of individual horizons shows a remarkable variability, both along strike and along dip of the fault. Since fault drag is a direct function of the displacement gradient quantification of this large scale fault drag allows identification of linked individual fault segments constraining the fault evolution. The investigated Markgrafneusiedl fault, crosscutting the Miocene sedimentary succession deposited from Carpathian up to the Pannonian age, represents the southeastern border of the Matzen oilfield. At depth, the Markgrafneusiedl fault displaces seismic horizons up to the decollement level, with a maximum throw of ~300 m. In order to visualize the three-dimensional distribution of fault drag throughout the seismic volume, six stratigraphic horizons were mapped in detail using the software package Seisvision (Landmark). An accurate stratigraphic correlation was achieved by integration of exploration well data located within the 3D seismic block. In order to document a greater number of marker horizons for the analysis of fault drag, the most distinctive seismic reflectors have been mapped throughout the entire cube in addition to the six well-documented formation tops. All horizons were mapped in TWT. Using the 3D modeling software Gocad (Paradigm), the mapped horizons tops were depth-converted, applying a generalized equation assuming an exponential increase of seismic velocity with depth. This conversion should ensure a better geometric representation of the fault drag geometries, which cannot be extracted from time-sections. The additional documentation of fault drag permits a more detailed identification of individual fault segments, which cannot be achieved by using conventional parameters, such as fault dip, azimuth and throw.

  17. Earthquake epicenters and fault intersections in central and southern California

    NASA Technical Reports Server (NTRS)

    Abdel-Gawad, M. (Principal Investigator); Silverstein, J.

    1972-01-01

    The author has identifed the following significant results. ERTS-1 imagery provided evidence for the existence of short transverse fault segments lodged between faults of the San Andreas system in the Coast Ranges, California. They indicate that an early episode of transverse shear has affected the Coast Ranges prior to the establishment of the present San Andreas fault. The fault has been offset by transverse faults of the Transverse Ranges. It appears feasible to identify from ERTS-1 imagery geomorphic criteria of recent fault movements. Plots of historic earthquakes in the Coast Ranges and western Transverse Ranges show clusters in areas where structures are complicated by interaction of tow active fault systems. A fault lineament apparently not previously mapped was identified in the Uinta Mountains, Utah. Part of the lineament show evidence of recent faulting which corresponds to a moderate earthquake cluster.

  18. Active Fault Deformation Along the South Boundary of the Western Transverse Ranges Province, Point Dume to the Northern Channel Islands, Southern California

    NASA Astrophysics Data System (ADS)

    Fisher, M. A.; Langenheim, V. E.; Sorlien, C. C.; Nicholson, C.; Sliter, R. W.

    2005-12-01

    The regional fault system forming the south boundary of the Western Transverse Ranges Province (WTRP) extends for about 200 km, from near the city of Los Angeles westward along the south flank of the Santa Monica Mountains and through the northern Channel Islands. Multichannel seismic-reflection data show that fault strands within the province-bounding system are active, and some have dip-slip displacements measured in kilometers. The left-oblique Dume fault is active and shows large displacement as far west as Sycamore knoll, but farther west, the fault tip and a superjacent fold are deeply buried. Thus during future earthquakes, the structural transition near the knoll could represent a boundary between earthquake-rupture segments. The east-west province-bounding fault system strikes at a high angle across and terminates the northwest-trending faults, basins and ridges of the California Continental Borderland. Borderland structures considered here form the western limit of intense middle Miocene oblique extension that accompanied rotation of the WTRP. The transition between extended and intact crust lies along the northwest-trending Santa Cruz-Catalina and Santa Rosa-Cortes Ridges. After the Miocene rotation, structures within these ridges became involved in regional transpression, such that northwestward along the Santa Cruz-Catalina Ridge, thrust faulting becomes increasingly more intense, and adjacent to the province boundary, thrust-faulted rocks completely override Miocene extensional structures. In contrast, rocks making up the Santa Rosa-Cortez Ridge are little deformed. The difference in deformation of the two ridges could result from a combination of: 1) eastward crustal thinning and consequent weakening that developed during the Miocene extension; 2) a difference in horizontal strain across the right-slip San Clemente fault near its termination at the WTRP boundary; 3) strain partitioning along this boundary; and 4) a contrast in bulk rheological

  19. Quaternary crustal deformation along a major branch of the San Andreas fault in central California

    USGS Publications Warehouse

    Weber, G.E.; Lajoie, K.R.; Wehmiller, J. F.

    1979-01-01

    Deformed marine terraces and alluvial deposits record Quaternary crustal deformation along segments of a major, seismically active branch of the San Andreas fault which extends 190 km SSE roughly parallel to the California coastline from Bolinas Lagoon to the Point Sur area. Most of this complex fault zone lies offshore (mapped by others using acoustical techniques), but a 4-km segment (Seal Cove fault) near Half Moon Bay and a 26-km segment (San Gregorio fault) between San Gregorio and Point Ano Nuevo lie onshore. At Half Moon Bay, right-lateral slip and N-S horizontal compression are expressed by a broad, synclinal warp in the first (lowest: 125 ka?) and second marine terraces on the NE side of the Seal Cove fault. This structure plunges to the west at an oblique angle into the fault plane. Linear, joint0controlled stream courses draining the coastal uplands are deflected toward the topographic depression along the synclinal axis where they emerge from the hills to cross the lowest terrace. Streams crossing the downwarped part of this terrace adjacent to Half Moon Bay are depositing alluvial fans, whereas streams crossing the uplifted southern limb of the syncline southwest of the bay are deeply incised. Minimum crustal shortening across this syncline parallel to the fault is 0.7% over the past 125 ka, based on deformation of the shoreline angle of the first terrace. Between San Gregorio and Point Ano Nuevo the entire fault zone is 2.5-3.0 km wide and has three primary traces or zones of faulting consisting of numerous en-echelon and anastomozing secondary fault traces. Lateral discontinuities and variable deformation of well-preserved marine terrace sequences help define major structural blocks and document differential motions in this area and south to Santa Cruz. Vertical displacement occurs on all of the fault traces, but is small compared to horizontal displacement. Some blocks within the fault zone are intensely faulted and steeply tilted. One major block 0

  20. Characterising the Alpine Fault Damage Zone using Fault Zone Guided Waves, South Westland, New Zealand

    NASA Astrophysics Data System (ADS)

    Eccles, J. D.; Gulley, A.; Boese, C. M.; Malin, P. E.; Townend, J.; Thurber, C. H.; Guo, B.; Sutherland, R.

    2015-12-01

    Fault Zone Guided Waves (FZGWs) are observed within New Zealand's transpressional continental plate boundary, the Alpine Fault, which is late in its typical seismic cycle. Distinctive dispersive seismic coda waves (~7-35 Hz), trapped within the low-velocity fault damage zone, have been recorded on three component 2 Hz borehole seismometers installed within 20 m of the principal slip zone in the shallow (< 150 m deep) DFDP-1 boreholes. Near the central Alpine Fault, known for low background seismicity, FZGW-generating microseismic events are located beyond the catchment-scale strike-slip and thrust segment partitioning of the fault indicating lateral connectivity of the low-velocity zone immediately below the near-surface segmentation. Double-difference earthquake relocation of events using the dense SAMBA and WIZARD seismometer arrays allows spatio-temporal patterns of 2013 events to be analysed and the segmentation and low velocity zone depth extent further explored. Three layer, dispersion modeling of the low-velocity zone indicates a waveguide width of 60-200 m with a 10-40% reduction in S-wave velocity, similar to that inferred for the fault core of other mature plate boundary faults such as the San Andreas and North Anatolian Faults.

  1. Tracing the Geomorphic Signature of Lateral Faulting

    NASA Astrophysics Data System (ADS)

    Duvall, A. R.; Tucker, G. E.

    2012-12-01

    Active strike-slip faults are among the most dangerous geologic features on Earth. Unfortunately, it is challenging to estimate their slip rates, seismic hazard, and evolution over a range of timescales. An under-exploited tool in strike-slip fault characterization is quantitative analysis of the geomorphic response to lateral fault motion to extract tectonic information directly from the landscape. Past geomorphic work of this kind has focused almost exclusively on vertical motion, despite the ubiquity of horizontal motion in crustal deformation and mountain building. We seek to address this problem by investigating the landscape response to strike-slip faulting in two ways: 1) examining the geomorphology of the Marlborough Fault System (MFS), a suite of parallel strike-slip faults within the actively deforming South Island of New Zealand, and 2) conducting controlled experiments in strike-slip landscape evolution using the CHILD landscape evolution model. The MFS offers an excellent natural experiment site because fault initiation ages and cumulative displacements decrease from north to south, whereas slip rates increase over four fold across a region underlain by a single bedrock unit (Torlesse Greywacke). Comparison of planform and longitudinal profiles of rivers draining the MFS reveals strong disequilibrium within tributaries that drain to active fault strands, and suggests that river capture related to fault activity may be a regular process in strike-slip fault zones. Simple model experiments support this view. Model calculations that include horizontal motion as well as vertical uplift demonstrate river lengthening and shortening due to stream capture in response to shutter ridges sliding in front of stream outlets. These results suggest that systematic variability in fluvial knickpoint location, drainage area, and incision rates along different faults or fault segments may be expected in catchments upstream of strike-slip faults and could act as useful

  2. Evolution of the Puente Hills Thrust Fault

    NASA Astrophysics Data System (ADS)

    Bergen, K. J.; Shaw, J. H.; Dolan, J. F.

    2013-12-01

    This study aims to assess the evolution of the blind Puente Hills thrust fault system (PHT) by determining its age of initiation, lateral propagation history, and changes in slip rate over time. The PHT presents one of the largest seismic hazards in the United States, given its location beneath downtown Los Angeles. The PHT is comprised of three fault segments: the Los Angeles (LA), Santa Fe Springs (SFS), and Coyote Hills (CH). The LA and SFS segments are characterized by growth stratigraphy where folds formed by uplift on the fault segments have been continually buried by sediment from the Los Angeles and San Gabriel rivers. The CH segment has developed topography and is characterized by onlapping growth stratigraphy. This depositional setting gives us the unique opportunity to measure uplift on the LA and SFS fault segments, and minimum uplift on the CH fault segment, as the difference in sediment thicknesses across the buried folds. We utilize depth converted oil industry seismic reflection data to image the fold geometries. Identifying time-correlative stratigraphic markers for slip rate determination in the basin has been a problem for researchers in the past, however, as the faunal assemblages observed in wells are time-transgressive by nature. To overcome this, we utilize the sequence stratigraphic model and well picks of Ponti et al. (2007) as a basis for mapping time-correlative sequence boundaries throughout our industry seismic reflection data from the present to the Pleistocene. From the Pleistocene to Miocene we identify additional sequence boundaries in our seismic reflection data from imaged sequence geometries and by correlating industry well formation tops. The sequence and formation top picks are then used to build 3-dimensional surfaces in the modeling program Gocad. From these surfaces we measure the change in thicknesses across the folds to obtain uplift rates between each sequence boundary. Our results show three distinct phases of

  3. Loading of the San Andreas fault by flood-induced rupture of faults beneath the Salton Sea

    USGS Publications Warehouse

    Brothers, Daniel; Kilb, Debi; Luttrell, Karen; Driscoll, Neal W.; Kent, Graham

    2011-01-01

    The southern San Andreas fault has not experienced a large earthquake for approximately 300 years, yet the previous five earthquakes occurred at ~180-year intervals. Large strike-slip faults are often segmented by lateral stepover zones. Movement on smaller faults within a stepover zone could perturb the main fault segments and potentially trigger a large earthquake. The southern San Andreas fault terminates in an extensional stepover zone beneath the Salton Sea—a lake that has experienced periodic flooding and desiccation since the late Holocene. Here we reconstruct the magnitude and timing of fault activity beneath the Salton Sea over several earthquake cycles. We observe coincident timing between flooding events, stepover fault displacement and ruptures on the San Andreas fault. Using Coulomb stress models, we show that the combined effect of lake loading, stepover fault movement and increased pore pressure could increase stress on the southern San Andreas fault to levels sufficient to induce failure. We conclude that rupture of the stepover faults, caused by periodic flooding of the palaeo-Salton Sea and by tectonic forcing, had the potential to trigger earthquake rupture on the southern San Andreas fault. Extensional stepover zones are highly susceptible to rapid stress loading and thus the Salton Sea may be a nucleation point for large ruptures on the southern San Andreas fault.

  4. A Quaternary Fault Database for Central Asia

    NASA Astrophysics Data System (ADS)

    Mohadjer, S.; Ehlers, T. A.; Bendick, R.; Stübner, K.; Strube, T.

    2015-09-01

    Earthquakes represent the highest risk in terms of potential loss of lives and economic damage for Central Asian countries. Knowledge of fault location and behavior is essential in calculating and mapping seismic hazard. Previous efforts in compiling fault information for Central Asia have generated a large amount of data that are published in limited-access journals with no digital maps publicly available, or are limited in their description of important fault parameters such as slip rates. This study builds on previous work by improving access to fault information through a web-based interactive map and an online database with search capabilities that allow users to organize data by different fields. The data presented in this compilation include fault location, its geographic, seismic and structural characteristics, short descriptions, narrative comments and references to peer-reviewed publications. The interactive map displays 1196 fault segments and 34 000 earthquake locations on a shaded-relief map. The online database contains attributes for 122 faults mentioned in the literature, with Quaternary and geodetic slip rates reported for 38 and 26 faults respectively, and earthquake history reported for 39 faults. This work has implications for seismic hazard studies in Central Asia as it summarizes important fault parameters, and can reduce earthquake risk by enhancing public access to information. It also allows scientists and hazard assessment teams to identify structures and regions where data gaps exist and future investigations are needed.

  5. Investigation of fault interaction and growth in Mygdonia basin (Greece) fault system

    NASA Astrophysics Data System (ADS)

    Gkarlaouni, Charikleia; Kilias, Adamantios; Papadimitriou, Eleftheria; Lasocki, Stanislaw; Karakostas, Vasileios

    2013-04-01

    Nowadays there is a scientific debate upon the strong correlation that exists between the earthquake clusters and the active seismogenic fault systems since they both constitute populations that participate in processes that include different states of initiation, interaction and coalescence. Since faults grow by the increase in their displacement and their length, the degree of fault interaction between two neighbour segments is expressed by scaling laws describing the fault dimensions, such as the displacement and the length. The distribution of the displacement along the fault trace, follows a bell-shaped pattern according to Dugdale model and is often a key to quantify the degree of interaction between two different fault segments since it gives an insight to the stage of growth and linkage between faults. In our case the fault attributes of Mygdonia basin that is located in the northern part of the Greek mainland are investigated under the prism of the scaling properties of its major active faults. Important seismogenic fault segments such as Lagina - Agios Vasilios, Gerakarou - Stivos and Sohos fault that define the boundaries of the basin and have generated important earthquakes in the past are investigated. Displacement - length profiles were constrained for the major fault segments, using digital elevation models (DEMs) since intense tectonics is etched upon the topography of the area such as to provide valuable seismotectonic information. In our case scarp heights are used for the approximation of fault displacement. Structural information, concerning displacement measurements on active fault scarps, and slip lineaments onto fault expressions are collected in-situ from field surveys. The information based on the field observations, justify the results coming out from the D.E.M. analysis. The final results are compared to conclusions derived from the investigation of different fault systems and the influence on the hazard assessment is discussed. This work

  6. Deformation associated with continental normal faults

    NASA Astrophysics Data System (ADS)

    Resor, Phillip G.

    Deformation associated with normal fault earthquakes and geologic structures provide insights into the seismic cycle as it unfolds over time scales from seconds to millions of years. Improved understanding of normal faulting will lead to more accurate seismic hazard assessments and prediction of associated structures. High-precision aftershock locations for the 1995 Kozani-Grevena earthquake (Mw 6.5), Greece image a segmented master fault and antithetic faults. This three-dimensional fault geometry is typical of normal fault systems mapped from outcrop or interpreted from reflection seismic data and illustrates the importance of incorporating three-dimensional fault geometry in mechanical models. Subsurface fault slip associated with the Kozani-Grevena and 1999 Hector Mine (Mw 7.1) earthquakes is modeled using a new method for slip inversion on three-dimensional fault surfaces. Incorporation of three-dimensional fault geometry improves the fit to the geodetic data while honoring aftershock distributions and surface ruptures. GPS Surveying of deformed bedding surfaces associated with normal faulting in the western Grand Canyon reveals patterns of deformation that are similar to those observed by interferometric satellite radar interferometry (InSAR) for the Kozani Grevena earthquake with a prominent down-warp in the hanging wall and a lesser up-warp in the footwall. However, deformation associated with the Kozani-Grevena earthquake extends ˜20 km from the fault surface trace, while the folds in the western Grand Canyon only extend 500 m into the footwall and 1500 m into the hanging wall. A comparison of mechanical and kinematic models illustrates advantages of mechanical models in exploring normal faulting processes including incorporation of both deformation and causative forces, and the opportunity to incorporate more complex fault geometry and constitutive properties. Elastic models with antithetic or synthetic faults or joints in association with a master

  7. Apparatus For Laminating Segmented Core For Electric Machine

    DOEpatents

    Lawrence, Robert Anthony; Stabel, Gerald R

    2003-06-17

    A segmented core for an electric machine includes segments stamped from coated electric steel. The segments each have a first end, a second end, and winding openings. A predetermined number of segments are placed end-to-end to form layers. The layers are stacked such that each of the layers is staggered from adjacent layers by a predetermined rotation angle. The winding openings of each of the layers are in vertical alignment with the winding openings of the adjacent layers. The stack of layers is secured to form the segmented core.

  8. Investigation of the Hosgri Fault, offshore Southern California, Point Sal to Point Conception

    USGS Publications Warehouse

    Payne, C.M.; Swanson, O.E.; Schell, B.A.

    1979-01-01

    A high-resolution seismic reflection survey of the inner continental shelf between Point Sal and Point Conception has revealed faults that displace post-Wisconsin strata (less than 17,000-20,000 years). These faults are the Hosgri fault, the Offshore Lompoc fault, and smaller unnamed faults. Faults trending offshore from the adjacent shoreline such as the Pezzoni, Lions Head, Honda, and Pacifico faults, do not show post-Wisconsin activity. The Hosgri fault trends directly toward the coastline between Purisima Point and Point Arguello where it appears to merge with folds and smaller faults in the western Transverse Ranges. This trend of offshore structures toward the Point Arguello-Point Conception area is consistent with a hypothesis that the regional structural fabric of the southern California Coast Ranges and its adjacent offshore area merge with the Transverse Ranges.

  9. Quaternary faults of west Texas

    SciTech Connect

    Collins, E.W.; Raney, J.A. . Bureau of Economic Geology)

    1993-04-01

    North- and northwest-striking intermontane basins and associated normal faults in West Texas and adjacent Chihuahua, Mexico, formed in response to Basin and Range tectonism that began about 24 Ma ago. Data on the precise ages of faulted and unfaulted Quaternary deposits are sparse. However, age estimates made on the basis of field stratigraphic relationships and the degree of calcic soil development have helped determine that many of the faults that bound the basin margins ruptured since the middle Pleistocene and that some faults probably ruptured during the Holocene. Average recurrence intervals between surface ruptures since the middle Pleistocene appear to be relatively long, about 10,000 to 100,000 yr. Maximum throw during single rupture events have been between 1 and 3 m. Historic seismicity in West Texas is low compared to seismicity in many parts of the Basin and Range province. The largest historic earthquake, the 1931 Valentine earthquake in Ryan Flat/Lobo Valley, had a magnitude of 6.4 and no reported surface rupture. The most active Quaternary faults occur within the 120-km-long Hueco Bolson, the 70-km-long Red Light Bolson, and the > 200-km-long Salt Basins/Wild Horse Flat/Lobo Valley/Ryan Flat.

  10. Spatial analysis of hypocenter to fault relationships for determining fault process zone width in Japan.

    SciTech Connect

    Arnold, Bill Walter; Roberts, Barry L.; McKenna, Sean Andrew; Coburn, Timothy C. (Abilene Christian University, Abilene, TX)

    2004-09-01

    Preliminary investigation areas (PIA) for a potential repository of high-level radioactive waste must be evaluated by NUMO with regard to a number of qualifying factors. One of these factors is related to earthquakes and fault activity. This study develops a spatial statistical assessment method that can be applied to the active faults in Japan to perform such screening evaluations. This analysis uses the distribution of seismicity near faults to define the width of the associated process zone. This concept is based on previous observations of aftershock earthquakes clustered near active faults and on the assumption that such seismic activity is indicative of fracturing and associated impacts on bedrock integrity. Preliminary analyses of aggregate data for all of Japan confirmed that the frequency of earthquakes is higher near active faults. Data used in the analysis were obtained from NUMO and consist of three primary sources: (1) active fault attributes compiled in a spreadsheet, (2) earthquake hypocenter data, and (3) active fault locations. Examination of these data revealed several limitations with regard to the ability to associate fault attributes from the spreadsheet to locations of individual fault trace segments. In particular, there was no direct link between attributes of the active faults in the spreadsheet and the active fault locations in the GIS database. In addition, the hypocenter location resolution in the pre-1983 data was less accurate than for later data. These pre-1983 hypocenters were eliminated from further analysis.

  11. Paleoseismic investigations in the Santa Cruz mountains, California: Implications for recurrence of large-magnitude earthquakes on the San Andreas Fault

    NASA Astrophysics Data System (ADS)

    Schwartz, D. P.; Pantosti, D.; Okumura, K.; Powers, T. J.; Hamilton, J. C.

    1998-08-01

    Trenching, microgeomorphic mapping, and tree ring analysis provide information on timing of paleoearthquakes and behavior of the San Andreas fault in the Santa Cruz mountains. At the Grizzly Flat site alluvial units dated at 1640-1659 A.D., 1679-1894 A.D., 1668-1893 A.D., and the present ground surface are displaced by a single event. This was the 1906 surface rupture. Combined trench dates and tree ring analysis suggest that the penultimate event occurred in the mid-1600 s, possibly in an interval as narrow as 1632-1659 A.D. There is no direct evidence in the trenches for the 1838 or 1865 earthquakes, which have been proposed as occurring on this part of the fault zone. In a minimum time of about 340 years only one large surface faulting event (1906) occurred at Grizzly Flat, in contrast to previous recurrence estimates of 95-110 years for the Santa Cruz mountains segment. Comparison with dates of the penultimate San Andreas earthquake at sites north of San Francisco suggests that the San Andreas fault between Point Arena and the Santa Cruz mountains may have failed either as a sequence of closely timed earthquakes on adjacent segments or as a single long rupture similar in length to the 1906 rupture around the mid-1600 s. The 1906 coseismic geodetic slip and the late Holocene geologic slip rate on the San Francisco peninsula and southward are about 50-70% and 70% of their values north of San Francisco, respectively. The slip gradient along the 1906 rupture section of the San Andreas reflects partitioning of plate boundary slip onto the San Gregorio, Sargent, and other faults south of the Golden Gate. If a mid-1600 s event ruptured the same section of the fault that failed in 1906, it supports the concept that long strike-slip faults can contain master rupture segments that repeat in both length and slip distribution. Recognition of a persistent slip rate gradient along the northern San Andreas fault and the concept of a master segment remove the requirement that

  12. Paleoseismic investigations in the Santa Cruz mountains, California: Implications for recurrence of large-magnitude earthquakes on the San Andreas fault

    USGS Publications Warehouse

    Schwartz, D.P.; Pantosti, D.; Okumura, K.; Powers, T.J.; Hamilton, J.C.

    1998-01-01

    Trenching, microgeomorphic mapping, and tree ring analysis provide information on timing of paleoearthquakes and behavior of the San Andreas fault in the Santa Cruz mountains. At the Grizzly Flat site alluvial units dated at 1640-1659 A.D., 1679-1894 A.D., 1668-1893 A.D., and the present ground surface are displaced by a single event. This was the 1906 surface rupture. Combined trench dates and tree ring analysis suggest that the penultimate event occurred in the mid-1600s, possibly in an interval as narrow as 1632-1659 A.D. There is no direct evidence in the trenches for the 1838 or 1865 earthquakes, which have been proposed as occurring on this part of the fault zone. In a minimum time of about 340 years only one large surface faulting event (1906) occurred at Grizzly Flat, in contrast to previous recurrence estimates of 95-110 years for the Santa Cruz mountains segment. Comparison with dates of the penultimate San Andreas earthquake at sites north of San Francisco suggests that the San Andreas fault between Point Arena and the Santa Cruz mountains may have failed either as a sequence of closely timed earthquakes on adjacent segments or as a single long rupture similar in length to the 1906 rupture around the mid-1600s. The 1906 coseismic geodetic slip and the late Holocene geologic slip rate on the San Francisco peninsula and southward are about 50-70% and 70% of their values north of San Francisco, respectively. The slip gradient along the 1906 rupture section of the San Andreas reflects partitioning of plate boundary slip onto the San Gregorio, Sargent, and other faults south of the Golden Gate. If a mid-1600s event ruptured the same section of the fault that failed in 1906, it supports the concept that long strike-slip faults can contain master rupture segments that repeat in both length and slip distribution. Recognition of a persistent slip rate gradient along the northern San Andreas fault and the concept of a master segment remove the requirement that

  13. Miocene extension and fault-related folding in the Highland Range, southern Nevada: A three-dimensional perspective

    USGS Publications Warehouse

    Faulds, J.E.; Olson, E.L.; Harlan, S.S.; McIntosh, W.C.

    2002-01-01

    The Highland Range of southern Nevada contains a major anticline and syncline that constitute the westernmost segments of the Black Mountains accommodation zone in the highly extended Colorado River extensional corridor. The folds are defined by thick tilted sections of Miocene volcanic and sedimentary strata that accumulated immediately prior to and during regional extension. The folds are generally symmetrical, with interlimb angles that exceed 90??, subhorizontal hingelines, and steeply inclined axial surfaces. East- and west-dipping normal faults dominate the west- and east-tilted limbs of the folds, respectively. The limbs of the folds are parts of major half grabens. Tilt fanning within these half grabens and 15 new 40Ar/39Ar dates bracket major extension between about 16.5 and 11 Ma. Tilting of the opposing fold limbs occurred simultaneously and was contemporaneous with extension. The anticline and syncline are therefore interpreted as fault-related extensional folds produced by the partial, along-strike overlap of oppositely dipping normal-fault systems and attendant tilt-block domains. The anticline developed between overlapping listric normal faults that dip toward one another, including the east-dipping McCullough Range and west-dipping Keyhole Canyon faults. Each limb of the anticline is a rollover fold developed in the hanging wall of the inwardly dipping listric normal faults. The syncline formed between overlapping outwardly dipping listric faults, as adjacent fault blocks were tilted toward one another. The dominant folding style was fault-bend folding, with drag-folding and displacement-gradient folding playing subsidiary roles. The anticline and syncline significantly affected depositional patterns, with synextensional units, including two major ash-flow tuffs, thinning toward the anticlinal hinge and thickening toward the synclinal hinge. The Black Mountains accommodation zone is largely composed of intersecting northwest-trending anticlines and

  14. Seismotectonic domains of northeastern India and adjacent areas

    NASA Astrophysics Data System (ADS)

    Nandy, D. R.; Dasgupta, Sujit

    Eastern Himalaya, Meghalaya plateau, upper Assam valley, northern part of the Indo-Burmese arc and the Mishmi block constitute major tectonostratigraphic domains in northeastern India. Many lineaments of faults, both parallel and oblique to the Himalayan trend, are already known. Interpretation of satellite images combined with surface geological studies suggest that many such oblique lineaments transgress the boundary of individual tectonic domains and some continue from the Tethyan Himalaya to the foredeep or cut across both Himalayan and Burmese arcs. The entire area is highly seismic; seismicity pattern, focal mechanism solutions, geological set up and fault/lineament fabric when studied together clearly defines several seismotectonic domains. In east Nepal-Sikkim, the northward push of India is accommodated through conjugate shear failure wherein seismic strike-slip movement occurs mostly along NE faults. Further east NW/WNW Kopili-Bomdila faults are associated with many large earthquakes and lateral motion along them allows a bulk southeastward movement of this segment of Himalaya towards the Burmese arc. The Mishmi block, structurally oblique to both the Himalayan and Burmese arcs, also indicates a net southeast tectonic transportation. The upper Assam valley is aseismic and arguably does not represent an area of seismic gap. Seismicity in both Meghalaya plateau and Sylhet plains is unrelated to movements along the Dauki fault.

  15. The North Maladeta Fault (Spanish Central Pyrenees) as the Vielha 1923 earthquake seismic source: Recent activity revealed by geomorphological and geophysical research

    NASA Astrophysics Data System (ADS)

    Ortuño, M.; Queralt, P.; Martí, A.; Ledo, J.; Masana, E.; Perea, H.; Santanach, P.

    2008-06-01

    The Spanish Central Pyrenees have been the scenario of at least two damaging earthquakes in the last 800 years. Analysis of macroseismic data of the most recent one, the Vielha earthquake (19 November 1923), has led to the identification of the North Maladeta Fault (NMF) as the seismic source of the event. This E-W trending fault defines the northern boundary of the Maladeta Batholith and corresponds to a segment of the Alpine Gavarnie thrust fault. Our study shows that the NMF offsets a reference Neogene peneplain. The maximum observed vertical displacement is ˜ 730 m, with the northern downthrown sector slightly tilting towards the South. This offset provides evidence of normal faulting and together with the presence of tectonic faceted spurs allowed us to geomorphically identify a fault trace of 17.5 km. This length suggests that a maximum earthquake of Mw = 6.5 ± 0.66 could occur in the area. The geomorphological study was improved with a resistivity model obtained at Prüedo, where a unique detritic Late Miocene sequence crops out adjacent to the NMF. The section is made up of 13 audiomagnetotelluric soundings along a 1.5 km transect perpendicular to the fault trace at Prüedo and reveals the structure in depth, allowing us to interpret the Late Miocene deposits as tectonically trapped basin deposits associated with normal faulting of the NMF. The indirect age of these deposits has been constrained between 11.1 and 8.7 Ma, which represents a minimum age for the elevated Pyrenean peneplain in this part of the Pyrenees. Therefore, we propose the maximum vertical dip-slip rate for the NMF to be between 0.06 and 0.08 mm/a. Normal faulting in this area is attributed to the vertical lithospheric stress associated with the thickened Pyrenean crust.

  16. Segmented amplifier configurations for laser amplifier

    DOEpatents

    Hagen, Wilhelm F.

    1979-01-01

    An amplifier system for high power lasers, the system comprising a compact array of segments which (1) preserves high, large signal gain with improved pumping efficiency and (2) allows the total amplifier length to be shortened by as much as one order of magnitude. The system uses a three dimensional array of segments, with the plane of each segment being oriented at substantially the amplifier medium Brewster angle relative to the incident laser beam and with one or more linear arrays of flashlamps positioned between adjacent rows of amplifier segments, with the plane of the linear array of flashlamps being substantially parallel to the beam propagation direction.

  17. Seismic velocity structure in the Hot Springs and Trifurcation areas of the San Jacinto fault zone, California, from double-difference tomography

    NASA Astrophysics Data System (ADS)

    Allam, A. A.; Ben-Zion, Y.; Kurzon, I.; Vernon, F.

    2014-08-01

    We present tomographic images of crustal velocity structures in the complex Hot Springs and Trifurcation areas of the San Jacinto Fault Zone (SJFZ) based on double-difference inversions of earthquake arrival times. We invert for VP, VS and hypocentre location within 50 × 50 × 20 km3 volumes, using 266 969 P and 148 249 S arrival times. We obtain high-fidelity images of seismic velocities with resolution on the order of a few kilometres from 2 to 12 km depth and validate the results using checkerboard tests. Due to the relatively large proportion of S-wave arrival times, we also obtain stable maps of VP/VS ratios in both regions. The velocity of the Trifurcation Area as a whole is lower than adjacent unfaulted material. We interpret a 4-km-wide low velocity zone with high VP/VS ratio in the trifurcation itself as related to fault zone damage. We also observe clear velocity contrasts across the Buck Ridge, Clark and Coyote Creek segments of the SJFZ. The Anza segment of the SJFZ, to the NW of the trifurcation area, displays a strong (up to 27 per cent) contrast of VS from 2 to 9 km depth. In the Hot Springs area, a low velocity zone between the Claremont and Casa Loma Strands narrows with depth, with clear velocity contrasts observed across both segments. A roughly 10-km-wide zone of low velocity and low VP/VS ratio at the NW tip of the Hot Springs fault is indicative of either unconsolidated sediments associated with the San Jacinto basin, or fluid-filled cracks within a broad deformation zone. High VP/VS ratios along the Anza segment could indicate a preferred nucleation location for future large earthquakes, while the across-fault velocity contrast suggests a preferred northwest rupture propagation direction for such events.

  18. Different styles of faulting deformation along the Dead Sea Transform and possible consequences for the recurrence of major earthquakes

    NASA Astrophysics Data System (ADS)

    Janssen, C.; Hoffmann-Rothe, A.; Bohnhoff, M.; Wetzel, H.-U.; Matar, A.; Khatib, M.; Desert Research Group

    2007-08-01

    We compare fault-related deformation of three segments of the major transform plate boundary between Africa and the Arabian plate, the Dead Sea Transform (DST), namely the Arava/Araba fault (Jordan/Israel), the Serghaya fault and the Ghab fault (both Syria). These segments show both similarities and marked differences in faulting deformation and fluid-rock interactions. In the case of the Arava fault, fault damage occurs across a zone up to 300 m wide. A fault core/gouge zone is not exhibited. Along the Serghaya fault, the typical fault zone architecture with a main gouge zone and a damage zone of up to 100 m thickness is exposed. Effects of faulting in the Ghab segment are shown by subsidiary faults and the formation of fault breccias. As in the Arava fault segment, a fault core is not exposed. Fluid-rock interactions are not equally distributed. At the Arava fault segment, the small amount of veins and the lack of alteration and dissolution processes in limestones suggest reduced fluid-rock interactions and limited fluid flow. The fault likely did not act as an important fluid conduit and hydrothermal reactions (cementation, dissolution) did not affect the strength of the fault zone. Contrary to the Arava fault, fluid-assisted fault zone healing processes (i.e. veining and cementation) were active along Serghaya fault and Ghab fault, where fault rock cementation led to porosity reduction and lower permeability. Such low permeability could create domains of higher pore fluid pressure, which reduce the effective shear stress required for slip on the fault. These differences in fluid-rock interactions may have played an important role with respect to the occurrence of earthquakes. We suggest that the recurrence interval on a fault segment that recovers after an earthquake without fluid assisted healing (e.g. Arava fault) should be longer than on segments with strong fluid-assisted healing (cementation; e.g. Serghaya fault, Ghab fault), given that the regional stress

  19. Surface Creep Along the East Anatolian Fault (Turkey) Revealed by InSAR Time Series: Implications for Seismic Hazard and Mechanism of Creep

    NASA Astrophysics Data System (ADS)

    Senturk, S.; Cakir, Z.; Ergintav, S.; Dogan, U.; Cetin, S.; Akoglu, A. M.; Meghraoui, M.; Karabulut, H.

    2015-12-01

    Forming the boundary between the Anatolian and Arabian plates in Turkey, the East Anatolian Fault (EAF) is a major tectonic structure in the Eastern Mediterranean region. Together with its conjugate, the North Anatolian Fault (NAF), it accommodates the westward motion of the Anatolian plate with respect to Eurasia. Although it has been associated only with small-to-moderate sized earthquakes in the instrumental period and relatively quiet compared to the North Anatolian Fault, the EAF produced devastating large (M > 7) earthquakes in the historical time (Ambraseys et al., 1998). Analysis of historical seismicity (Nalbant et al., 2001) suggests that a seismic gap exists between the Lake of Hazar and Bingöl, referred here as to Palu seismic gap (PSG) We estimate the interseismic velocity field along the BSG using the Persistent Scatterer InSAR technique (Hooper, 2008). ENVISAT ASAR data acquired between 2003 and 2010 on three adjacent descending and overlapping tracks (T035, T264 and T493) are use to map the interseismic strain accumulation. The results reveal that the 100-km-long section of the Palu segment is exhibiting aseismic creep at the surface. The creep rate varies along the fault reaching, at some places, to the far field GPS-based plate velocity (i.e., 10 ± 0.3 mm/y; Reilinger et al., 2006), implying that significant portion of the elastic strain has been released aseismically. Preliminary modelling with elastic dislocations suggests that some sections of the fault may be creeping from surface down to the entire seismogenic crust. Geology of the fault zone is dominated by ophiolitic and volcanic rocks characterized by weak phyllosilicate minerals, suggesting that aseismic slip is promoted by minerals with low frictional properties. Furthermore, to monitor the surface creep, a GPS network has been established along the Palu segment. One survey has so far been realized and we expect the reliable results in 2 years (supported by TUBITAK no: 114Y250 project).

  20. Ground-motion signature of dynamic ruptures on rough faults

    NASA Astrophysics Data System (ADS)

    Mai, P. Martin; Galis, Martin; Thingbaijam, Kiran K. S.; Vyas, Jagdish C.

    2016-04-01

    Natural earthquakes occur on faults characterized by large-scale segmentation and small-scale roughness. This multi-scale geometrical complexity controls the dynamic rupture process, and hence strongly affects the radiated seismic waves and near-field shaking. For a fault system with given segmentation, the question arises what are the conditions for producing large-magnitude multi-segment ruptures, as opposed to smaller single-segment events. Similarly, for variable degrees of roughness, ruptures may be arrested prematurely or may break the entire fault. In addition, fault roughness induces rupture incoherence that determines the level of high-frequency radiation. Using HPC-enabled dynamic-rupture simulations, we generate physically self-consistent rough-fault earthquake scenarios (M~6.8) and their associated near-source seismic radiation. Because these computations are too expensive to be conducted routinely for simulation-based seismic hazard assessment, we thrive to develop an effective pseudo-dynamic source characterization that produces (almost) the same ground-motion characteristics. Therefore, we examine how variable degrees of fault roughness affect rupture properties and the seismic wavefield, and develop a planar-fault kinematic source representation that emulates the observed dynamic behaviour. We propose an effective workflow for improved pseudo-dynamic source modelling that incorporates rough-fault effects and its associated high-frequency radiation in broadband ground-motion computation for simulation-based seismic hazard assessment.

  1. Do transform faults parallel plate motion?

    NASA Astrophysics Data System (ADS)

    Mishra, J. K.; Gordon, R. G.; Demets, C.; Argus, D.

    2009-12-01

    A central principle of plate tectonics is that relative plate motion is parallel to transform faults. Several workers have convincingly argued, however, that transform fault valleys widen with age due to horizontal thermal contraction of the lithosphere [Collette 1974; Roest et al 1986 ; Sandwell 1986]. If so, then the transform fault zone, which is the locus of active strike-slip faulting in a transform fault, may not be parallel to the direction of relative plate motion, but parallel to the relative velocity of the walls of the transform valley. Here we apply a recent model for horizontal contraction of oceanic lithosphere as a function of age [Kumar & Gordon 2009] to calculate this bias in transform azimuth as a function of offset, spreading rate, and ridge length, with slightly different formulations for crenelate and stepping mid-ocean ridge segments. The calculated bias increases with increasing length of ridge segments between transform faults and decreases with increasing offset of ridge segments along transform faults. We used the calculated bias to estimate corrections of azimuths of transform faults on eight plate boundaries from the MORVEL data set [DeMets, Argus, & Gordon, 2009]. The largest correction is 2.3 degrees, but the median correction is merely 0.2 degrees. We express the null hypothesis (no thermal contraction) and our hypothesis (thermal contraction as predicted by Kumar and Gordon [2009]), in terms of a parameter α, which is zero for no thermal contraction and 1 for predicted thermal contraction. When the results for the 8 plate pairs are combined, we find that α = 1.1 ± 0.7 (95% confidence limits), thus excluding the null hypothesis (no thermal contraction), but consistent with the hypothesis of horizontal thermal contraction.

  2. Preliminary investigation of factors affecting the seismic potential of the Bartlett Springs fault zone, northern California

    NASA Astrophysics Data System (ADS)

    Lienkaemper, J. J.; Brown, J.

    2009-12-01

    discontinuities, the state of stress relative to the failure stress of each section and the timing and extent of previous ruptures. Microseismicity distribution is also relevant to seismic potential, because it tends to correlate with fault creep. The central third of the BSF has high microseismicity and with respect to with the plate boundary its strike ranges from transtensional to parallel, thus favoring stable sliding and unclamping. Our mapping indicates the largest BSF discontinuities are a 2.5-km left stepover at the Middle Fork of the Eel River and a 2.5-km right stepover at Wilson Valley. Some previous hazard models have assumed the BFS is likely to have a complete 170-km rupture of Mw~7.2, however, shorter rupture scenarios may be much more likely. For example, one more plausible rupture, for the ~70-km central section having high microseismicity, yields Mw~6.8, because its rupture would tend to terminate in the adjacent sections oriented favorably to locking. Many other plausible scenarios for segments of varying length can be posed, each needing to be weighted inversely to the likely difficulty of each rupture to occur.

  3. Analysis of the growth of strike-slip faults using effective medium theory

    SciTech Connect

    Aydin, A.; Berryman, J.G.

    2009-10-15

    Increases in the dimensions of strike-slip faults including fault length, thickness of fault rock and the surrounding damage zone collectively provide quantitative definition of fault growth and are commonly measured in terms of the maximum fault slip. The field observations indicate that a common mechanism for fault growth in the brittle upper crust is fault lengthening by linkage and coalescence of neighboring fault segments or strands, and fault rock-zone widening into highly fractured inner damage zone via cataclastic deformation. The most important underlying mechanical reason in both cases is prior weakening of the rocks surrounding a fault's core and between neighboring fault segments by faulting-related fractures. In this paper, using field observations together with effective medium models, we analyze the reduction in the effective elastic properties of rock in terms of density of the fault-related brittle fractures and fracture intersection angles controlled primarily by the splay angles. Fracture densities or equivalent fracture spacing values corresponding to the vanishing Young's, shear, and quasi-pure shear moduli were obtained by extrapolation from the calculated range of these parameters. The fracture densities or the equivalent spacing values obtained using this method compare well with the field data measured along scan lines across the faults in the study area. These findings should be helpful for a better understanding of the fracture density/spacing distribution around faults and the transition from discrete fracturing to cataclastic deformation associated with fault growth and the related instabilities.

  4. Fault depth and seismic moment rate estimates of the San Andreas Fault System: Observations from seismology and geodesy

    NASA Astrophysics Data System (ADS)

    Smith-Konter, B. R.; Sandwell, D. T.; Shearer, P. M.

    2010-12-01

    The depth of the seismogenic zone is a critical parameter for earthquake hazard models of the San Andreas Fault System. Independent observations from both seismology and geodesy can provide insight into the depths of faulting, however these depths do not always agree. Here we inspect variations in fault depths of 12 segments of the southern San Andreas Fault System derived from over 1000 GPS velocities and 66,000 relocated earthquake hypocenters. Geodetically-determined locking depths range from 6-22 km, while seismogenic thicknesses are largely limited to depths of 11-20 km. Seismogenic depths best match the geodetic locking depths when estimated at the 95% cutoff depth in seismicity and most fault segment depths agree to within 2 km. However, we identify 3 outliers (Imperial, Coyote Creek, and Borrego segments) with significant discrepancies. In these cases the geodetically-inferred locking depths are much shallower than the seismogenic depths. We also inspect seismic moment accumulation rates per unit fault length, with the highest rates estimated for the Mojave and Carrizo segments (~1.8 x 1013 Nm/yr/km) and the lowest rates (~0.2 x 1013 Nm/yr/km) found along several San Jacinto segments. The largest variation in seismic moment is calculated for the Imperial segment, where the moment rate from seismic depths is nearly a factor of 2.5 larger than that from geodetic depths. Such variability has important implications for the accuracy to which the magnitude of future major earthquakes can be estimated.

  5. Finite-fault analysis of the 1979 March 14 Petatlan, Mexico, earthquake using teleseismic P waveforms

    USGS Publications Warehouse

    Mendoza, C.

    1995-01-01

    Vertical, teleseismic P waves recorded for the 1979 March 14 Petatlan, Mexico, earthquake were used to derive the distribution of coseismic slip using a linear finite-fault inversion scheme that solves for the amount of slip in each of a series of consecutive time windows. The coseismic slip inferred from the P waves shows a small 70 cm peak near the earthquake hypocentre and a large zone of dislocation (1.2 m maximum) further south-east. The slip pattern covers depths from 3 to 25 km and is located south-east of other recent large interplate ruptures on the Michoacan segment of the Mexican subduction zone. This result indicates that the 1979 Petatlan earthquake broke an independent, adjacent portion of the Cocos-North America plate boundary. -from Author

  6. Active tectonics of the Seattle fault and central Puget sound, Washington - Implications for earthquake hazards

    USGS Publications Warehouse

    Johnson, S.Y.; Dadisman, S.V.; Childs, J. R.; Stanley, W.D.

    1999-01-01

    We use an extensive network of marine high-resolution and conventional industry seismic-reflection data to constrain the location, shallow structure, and displacement rates of the Seattle fault zone and crosscutting high-angle faults in the Puget Lowland of western Washington. Analysis of seismic profiles extending 50 km across the Puget Lowland from Lake Washington to Hood Canal indicates that the west-trending Seattle fault comprises a broad (4-6 km) zone of three or more south-dipping reverse faults. Quaternary sediment has been folded and faulted along all faults in the zone but is clearly most pronounced along fault A, the northernmost fault, which forms the boundary between the Seattle uplift and Seattle basin. Analysis of growth strata deposited across fault A indicate minimum Quaternary slip rates of about 0.6 mm/yr. Slip rates across the entire zone are estimated to be 0.7-1.1 mm/yr. The Seattle fault is cut into two main segments by an active, north-trending, high-angle, strike-slip fault zone with cumulative dextral displacement of about 2.4 km. Faults in this zone truncate and warp reflections in Tertiary and Quaternary strata and locally coincide with bathymetric lineaments. Cumulative slip rates on these faults may exceed 0.2 mm/yr. Assuming no other crosscutting faults, this north-trending fault zone divides the Seattle fault into 30-40-km-long western and eastern segments. Although this geometry could limit the area ruptured in some Seattle fault earthquakes, a large event ca. A.D. 900 appears to have involved both segments. Regional seismic-hazard assessments must (1) incorporate new information on fault length, geometry, and displacement rates on the Seattle fault, and (2) consider the hazard presented by the previously unrecognized, north-trending fault zone.

  7. Eastern Denali Fault Slip Rate and Paleoseismic History, Kluane Lake Area, Yukon Territory, Canada

    NASA Astrophysics Data System (ADS)

    Seitz, G. J.; Haeussler, P. J.; Crone, A. J.; Lipovsky, P.; Schwartz, D. P.

    2008-12-01

    In 2002, the central part of the dextral-slip Denali fault (DF) system generated a M 7.9 earthquake in central Alaska. This rupture included the section of the Denali fault with the highest measured late Pleistocene slip rate, of 12.1±1.7 mm/yr, and the Totschunda fault, with a slip rate of 6.0±1.2 mm/yr. Immediately east of the Denali-Totschunda fault juncture, the slip rate on the eastern Denali fault (EDF) decreases to 8.4±2.2 mm/yr. We present observations of Holocene fault activity on the Yukon part of the EDF (Shakwak segment), which is located about 280 km southeast of the Denali-Totschunda intersection in the vicinity of Kluane Lake. Aerial reconnaissance in 2007, from the Denali-Totschunda fault juncture to the Kluane Lake region revealed a nearly continuously identifiable fault trace, which is occasionally obscured where it is subparallel to glacial landforms. In addition to geomorphic features associated with strike-slip faults, such as shutter ridges and sag ponds, the fault is commonly expressed by a chain of elongate mounds, likely tectonic pushups, 20-70 m in length, 10-50 m wide, and locally up to 10 m high. These appear to have formed by shortening between en echelon left-stepping fault strands that developed in layered glacial sediments. At one location (61°18'30.12" N, 139°01'02.54"W) we measured on the ground a channel offset of 20-25 m. An aerial view showed that other channels in the vicinity, as well as the margins of two mounds, were offset by similar amounts. These channels likely developed after deglaciation 10-12 ka. Using this age and the offset yields a slip-rate range of 1.7-2.5 mm/yr, a minimum value but one that may be close to the actual rate. However, because of uncertainties in age relations between construction of the uplift mounds and channel incision the offset could be younger and we estimate an upper limit of about 5 mm/yr. Adjacent to and south of the Duke River, an approximately 2-km-long section of the fault is

  8. The Dume Fault, Northern Santa Monica Bay, California

    NASA Astrophysics Data System (ADS)

    Sorlien, C. C.; Kamerling, M. J.; Seeber, L.

    2001-12-01

    We used industry seismic reflection and well data to create digital structure-contour maps beneath northern Santa Monica Bay. These maps include a principal strand of the Dume fault and a deformed horizon within the Pliocene Repetto Formation. This horizon is mapped 50 km from Pt. Dume westward to Port Hueneme and 20 km southward from the Malibu Coast-Santa Cruz Island fault across the Dume fault to the NW-striking faults and folds of the San Pedro system. The Dume fault dips gently-to-moderately north, and its hanging-wall is cut by the subvertical Malibu Coast fault. The overall strike of the Dume fault is to the west, but is arcuate, being north-concave on the east half of our study area and north-convex on the west. A W-dipping lateral ramp occurs within the WNW-striking segment. This lateral ramp coincides in space with the intersection of the Dume fault with an underlying blind NW-SE Borderlands fault. There is little shortening across the ENE-striking segment and over 3 km of shortening at the culmination of a double-plunging hanging-wall anticline along the WNW-striking segment. This anticline forms Sycamore Knoll and plunges abruptly west above the lateral ramp. The Pliocene horizon and the top Miocene volcanics can be correlated across the Dume fault and related fold, around its east and west plunges and also along its hanging-wall and footwall blocks. The interval between these horizons is thicker on the upthrown hanging-wall side of the fault, which is consistent with basin inversion. The folding initiated during the Repettian Stage and accelerated towards the end of this stage. Preliminary kinematic analysis suggests that the Dume fault is predominantly left-lateral in its ENE segment. Regional south dip in the hanging-wall of this segment represents 1-2 km of offshore structural relief in the Pliocene horizon. This relief may reflect a blind dip-slip component absorbed by folding at the scale of the Santa Monica Mountains. A 700 m-high seafloor scarp

  9. Modeling of Stress Triggered Faulting at Agenor Linea, Europa

    NASA Astrophysics Data System (ADS)

    Nahm, A. L.; Cameron, M. E.; Smith-Konter, B. R.; Pappalardo, R. T.

    2012-04-01

    , while normal stresses control a fault's frictional resistance to failure. According to this model,shear failure will occur when the shear stress exceeds the frictional resistance of the fault. We find that diurnal plus NSR stresses allow for shear failure along Agenor Linea; this result is very sensitive to fault depth, with the western end of the fault failing at shallow depths (< 3 km) and the eastern end failing at 3 - 4 km depths. Complementary to the stress accumulation model, we also calculate coseismic displacements along fault segments that meet the conditions for shear failure. Displacement calculations assume a conservative estimate of stress drop in the slip events, 10% of the total stress, although we also investigate the implication of complete stress drop in alternative models. Stress drops on the order of 10-1 MPa are calculated, consistent with terrestrial ice quake values of 10-4 - 10-1 MPa; resulting displacements reach a maximum of ~2 m. These displacements are used as input for the forward mechanical disclocation model COULOMB, where a fault surface is idealized as a rectangular plane for which the sense of slip, magnitude of displacement, fault dip angle, depth of faulting, and fault length are specified, and the Coulomb stress change in the volume surrounding the fault is calculated. Positive Coulomb stress changes (promoting failure) ranging between 0 and 1.0 MPa (mean 2.4 - 10-4 MPa) are calculated for vertical faults ~4 km long with depths of 3 - 4 km. These positive stress changes are primarily confined to small regions (~50 km in length) adjacent to the west and east tips of major strands with prescribed displacement, indicating fault growth is possible in these locations. Positive stress change is also observed at the intersection of the branches with the main fault, indicating that slip is likely to initiate there. Future work consists of evaluating other failure scenarios and range of stress drops and associated displacements combined with

  10. Compound fault diagnosis of gearboxes based on GFT component extraction

    NASA Astrophysics Data System (ADS)

    Ou, Lu; Yu, Dejie

    2016-11-01

    Compound fault diagnosis of gearboxes is of great importance to the long-term safe operation of rotating machines, and the key is to separate different fault components. In this paper, the path graph is introduced into the vibration signal analysis and the graph Fourier transform (GFT) of vibration signals are investigated from the graph spectrum domain. To better extract the fault components in gearboxes, a new adjacency weight matrix is defined and then the GFT of simulation signals of the gear and the bearing with localized faults are analyzed. Further, since the GFT graph spectrum of the gear fault component and the bearing fault component are mainly distributed in the low-order region and the high-order region, respectively, a novel method for the compound fault diagnosis of gearboxes based on GFT component extraction is proposed. In this method, the nonzero ratios, which are introduced to analyze the eigenvectors auxiliary, and the GFT of a gearbox vibration signal, are firstly calculated. Then, the order thresholds for reconstructed fault components are determined and the fault components are extracted. Finally, the Hilbert demodulation analyses are conducted. According to the envelope spectra of the fault components, the faults of the gear and the bearing can be diagnosed respectively. The performance of the proposed method is validated by the simulation data and the experiment signals from a gearbox with compound faults.

  11. Structural styles of Paleozoic intracratonic fault reactivation: A case study of the Grays Point fault zone in southeastern Missouri, USA

    USGS Publications Warehouse

    Clendenin, C.W.; Diehl, S.F.

    1999-01-01

    A pronounced, subparallel set of northeast-striking faults occurs in southeastern Missouri, but little is known about these faults because of poor exposure. The Commerce fault system is the southernmost exposed fault system in this set and has an ancestry related to Reelfoot rift extension. Recent published work indicates that this fault system has a long history of reactivation. The northeast-striking Grays Point fault zone is a segment of the Commerce fault system and is well exposed along the southeast rim of an inactive quarry. Our mapping shows that the Grays Point fault zone also has a complex history of polyphase reactivation, involving three periods of Paleozoic reactivation that occurred in Late Ordovician, Devonian, and post-Mississippian. Each period is characterized by divergent, right-lateral oblique-slip faulting. Petrographic examination of sidwall rip-out clasts in calcite-filled faults associated with the Grays Point fault zone supports a minimum of three periods of right-lateral oblique-slip. The reported observations imply that a genetic link exists between intracratonic fault reactivation and strain produced by Paleozoic orogenies affecting the eastern margin of Laurentia (North America). Interpretation of this link indicate that right-lateral oblique-slip has occurred on all of the northeast-striking faults in southeastern Missouri as a result of strain influenced by the convergence directions of the different Paleozoic orogenies.

  12. Multiple episodes of breccia formation by particle fluidization in fault zones: implications repeated, rupture-controlled fluid flow and seismicity styles

    NASA Astrophysics Data System (ADS)

    Cox, Stephen

    2016-04-01

    Breccias in the Rusey Fault (Cornwall, UK) provide insights about the dynamics of fault behaviour, fluid flow and flow velocities when fault ruptures breach overpressured reservoirs of hydrothermal fluid. The 3 m wide fault core comprises a mix of breccias, banded cataclasites, probable psuedotachylites and extension veins. The damage products are dominated by high dilation breccias with cockade-like textures in which rock fragments are mantled by spheroidal overgrowths of quartz. Although none of the rock fragment cores of accretionary spheroids are in contact with their neighbours, the spheroidal overgrowths do contact each other and are at least partially cemented together. The hydrothermal overgrowths mostly comprise either outwards coarsening crystals that radiate from the surface of the core particle, or finer-grained, inequigranular to mesh-like intergrowths. Concentric textural banding and oscillatory growth zones are present in some hydrothermal overgrowths. The breccias occur as fault-parallel layers and lenses, each up to several tens of centimeter thick. Adjacent layers are characterised by texturally-distinct ranges of clast sizes and different proportions of clasts to hydrothermal overgrowths. Many texturally-distinct breccia layers are present within the fault core. Some breccia layers truncate others and many breccia layers exhibit grainsize grading or banding. Clasts in the breccias include fragments of wall-rock, veins and various fault damage products, including fragments of earlier generations of cemented breccia. As brecciation was episodic and separated by periods of cementation, the breccias are interpreted to have formed as a consequence of repeated seismogenic failure. The distinctive textures in the breccias are interpreted to have formed by fluidization of fault damage products in a high fluid flux regime, with each breccia layer being the product of one, rupture-related flow episode. Hydrothermal coatings developed while clasts were in a

  13. Fault structure and mechanics of the Hayward Fault, California from double-difference earthquake locations

    USGS Publications Warehouse

    Waldhauser, F.; Ellsworth, W.L.

    2002-01-01

    The relationship between small-magnitude seismicity and large-scale crustal faulting along the Hayward Fault, California, is investigated using a double-difference (DD) earthquake location algorithm. We used the DD method to determine high-resolution hypocenter locations of the seismicity that occurred between 1967 and 1998. The DD technique incorporates catalog travel time data and relative P and S wave arrival time measurements from waveform cross correlation to solve for the hypocentral separation between events. The relocated seismicity reveals a narrow, near-vertical fault zone at most locations. This zone follows the Hayward Fault along its northern half and then diverges from it to the east near San Leandro, forming the Mission trend. The relocated seismicity is consistent with the idea that slip from the Calaveras Fault is transferred over the Mission trend onto the northern Hayward Fault. The Mission trend is not clearly associated with any mapped active fault as it continues to the south and joins the Calaveras Fault at Calaveras Reservoir. In some locations, discrete structures adjacent to the main trace are seen, features that were previously hidden in the uncertainty of the network locations. The fine structure of the seismicity suggest that the fault surface on the northern Hayward Fault is curved or that the events occur on several substructures. Near San Leandro, where the more westerly striking trend of the Mission seismicity intersects with the surface trace of the (aseismic) southern Hayward Fault, the seismicity remains diffuse after relocation, with strong variation in focal mechanisms between adjacent events indicating a highly fractured zone of deformation. The seismicity is highly organized in space, especially on the northern Hayward Fault, where it forms horizontal, slip-parallel streaks of hypocenters of only a few tens of meters width, bounded by areas almost absent of seismic activity. During the interval from 1984 to 1998, when digital

  14. Dynamic leakage of faults during differential depletion: Theory, models, and examples from the Niger delta

    SciTech Connect

    Watts, N.L.; Kaars Sijpestein, C.H.; Osai, L.N.; Okoli, O.C. )

    1991-08-01

    Previous studies of fault sealing have addressed possible fault leakage during secondary migration due to the effects of increased hydrocarbon-water capillary pressure, fracturing, or small-scale incremental fault movements. Of equal importance to production geologists is the failure and leakage of faults during field development due to differential depletion of adjacent fault blocks. This paper examines the unique problems associated with this dynamic leakage of faults. It is theoretically shown that the fault sealing mechanism, and the extent of the seal, directly influences the failure process which in turn results in a variety of favorable and unfavorable effects on field development. The qualitative models give considerable insight into such aspects as oil-column expansion and resaturation losses, interfault block aquifer support (with important implications to material balance calculations), possible leakage or spillage of oil across faults, and potential fault failure during (re)injection projects. Examples of dynamic fault leakage are presented from selected fields of the Niger delta.

  15. Geodetic constraints on San Francisco Bay Area fault slip rates and potential seismogenic asperities on the partially creeping Hayward fault

    NASA Astrophysics Data System (ADS)

    Evans, Eileen L.; Loveless, John P.; Meade, Brendan J.

    2012-03-01

    The Hayward fault in the San Francisco Bay Area (SFBA) is sometimes considered unusual among continental faults for exhibiting significant aseismic creep during the interseismic phase of the seismic cycle while also generating sufficient elastic strain to produce major earthquakes. Imaging the spatial variation in interseismic fault creep on the Hayward fault is complicated because of the interseismic strain accumulation associated with nearby faults in the SFBA, where the relative motion between the Pacific plate and the Sierra block is partitioned across closely spaced subparallel faults. To estimate spatially variable creep on the Hayward fault, we interpret geodetic observations with a three-dimensional kinematically consistent block model of the SFBA fault system. Resolution tests reveal that creep rate variations with a length scale of <15 km are poorly resolved below 7 km depth. In addition, creep at depth may be sensitive to assumptions about the kinematic consistency of fault slip rate models. Differential microplate motions result in a slip rate of 6.7 ± 0.8 mm/yr on the Hayward fault, and we image along-strike variations in slip deficit rate at ˜15 km length scales shallower than 7 km depth. Similar to previous studies, we identify a strongly coupled asperity with a slip deficit rate of up to 4 mm/yr on the central Hayward fault that is spatially correlated with the mapped surface trace of the 1868 MW = 6.9-7.0 Hayward earthquake and adjacent to gabbroic fault surfaces.

  16. Fault-controlled geomorphology and paleoseismology of Fethiye fault and gulf

    NASA Astrophysics Data System (ADS)

    Chatzipetros, Alexandros; Pavlides, Spyros; Yaǧmurlu, Fuzuli; Özgür, Nevzat; Kamaci, Züheyr; Şentürk, Murat

    2010-05-01

    Fethiye gulf is located at the south-westernmost part of the large left-lateral Fethiye-Burdur fault zone. It is modified and controlled by sets of NE - SW trending normal and oblique left-lateral faults. The gulf forms coastlines that are often aligned nearly perpendicular to one another. Coastlines are mainly NE - SW trending and they are inundated by small bays, mainly in NNW-SSE direction. Those directions are comparable to the main mainland fault lines, as measured on outcrops in the area. The brittle features of the area overprint the pre-existing tectonic fabric of low-angle thrusts and pure strike-slip faults. Recent activity of the faults seems to be possible, since there is indication for hangingwall submergence at the "Cleopatra's bath" site, where an early-Byzantine building complex has been submerged by at least 2 m. The mainland active fault zone is located S-SE of Fethiye town and it forms an N-NW dipping fault scarp that is characterized by multiple en échelon segments. The quantitative tectonic geomorphology of this fault has been studied by using morphotectonic indices (scarp sinuosity, valley width/depth ratio, etc.), which show that the fault has a rather low level of activity. Nevertheless, the fault zone near Fethiye presents other morphotectonic features, such as riverbed catchment, slight left-lateral bend of streams at the foot of the scarp, etc. The fault zone seems to fan out towards the west and the deformation is less evident. Although the fault segments near Fethiye are classified as low-activity ones, they are associated with the large 1957 earthquake (Ms 7.1). This earthquake produced extensive damage and casualties. It was physically manifested by surface ruptures, rockfalls, etc. A palaeoseismological survey has been carried out in the area. Trenches in two different segments show that the 1957 surface rupture is traceable along the fault, while at least two previous events seem to have affected the area and produced surface

  17. Molecular disorganization of axons adjacent to human lacunar infarcts.

    PubMed

    Hinman, Jason D; Lee, Monica D; Tung, Spencer; Vinters, Harry V; Carmichael, S Thomas

    2015-03-01

    Cerebral microvascular disease predominantly affects brain white matter and deep grey matter, resulting in ischaemic damage that ranges from lacunar infarcts to white matter hyperintensities seen on magnetic resonance imaging. These lesions are common and result in both clinical stroke syndromes and accumulate over time, resulting in cognitive deficits and dementia. Magnetic resonance imaging studies suggest that these lesions progress over time, accumulate adjacent to prior lesions and have a penumbral region susceptible to further injury. The pathological correlates of this adjacent injury in surviving myelinated axons have not been previously defined. In this study, we sought to determine the molecular organization of axons in tissue adjacent to lacunar infarcts and in the regions surrounding microinfarcts, by determining critical elements in axonal function: the morphology and length of node of Ranvier segments and adjacent paranodal segments. We examined post-mortem brain tissue from six patients with lacunar infarcts and tissue from two patients with autosomal dominant retinal vasculopathy and cerebral leukoencephalopathy (previously known as hereditary endotheliopathy with retinopathy, nephropathy and stroke) who accumulate progressive white matter ischaemic lesions in the form of lacunar and microinfarcts. In axons adjacent to lacunar infarcts yet extending up to 150% of the infarct diameter away, both nodal and paranodal length increase by ∼20% and 80%, respectively, reflecting a loss of normal cell-cell adhesion and signalling between axons and oligodendrocytes. Using premorbid magnetic resonance images, brain regions from patients with retinal vasculopathy and cerebral leukoencephalopathy that harboured periventricular white matter hyperintensities were selected and the molecular organization of axons was determined within these regions. As in regions adjacent to lacunar infarcts, nodal and paranodal length in white matter of these patients is

  18. Molecular disorganization of axons adjacent to human lacunar infarcts

    PubMed Central

    Lee, Monica D.; Tung, Spencer; Vinters, Harry V.; Carmichael, S. Thomas

    2015-01-01

    Cerebral microvascular disease predominantly affects brain white matter and deep grey matter, resulting in ischaemic damage that ranges from lacunar infarcts to white matter hyperintensities seen on magnetic resonance imaging. These lesions are common and result in both clinical stroke syndromes and accumulate over time, resulting in cognitive deficits and dementia. Magnetic resonance imaging studies suggest that these lesions progress over time, accumulate adjacent to prior lesions and have a penumbral region susceptible to further injury. The pathological correlates of this adjacent injury in surviving myelinated axons have not been previously defined. In this study, we sought to determine the molecular organization of axons in tissue adjacent to lacunar infarcts and in the regions surrounding microinfarcts, by determining critical elements in axonal function: the morphology and length of node of Ranvier segments and adjacent paranodal segments. We examined post-mortem brain tissue from six patients with lacunar infarcts and tissue from two patients with autosomal dominant retinal vasculopathy and cerebral leukoencephalopathy (previously known as hereditary endotheliopathy with retinopathy, nephropathy and stroke) who accumulate progressive white matter ischaemic lesions in the form of lacunar and microinfarcts. In axons adjacent to lacunar infarcts yet extending up to 150% of the infarct diameter away, both nodal and paranodal length increase by ∼20% and 80%, respectively, reflecting a loss of normal cell-cell adhesion and signalling between axons and oligodendrocytes. Using premorbid magnetic resonance images, brain regions from patients with retinal vasculopathy and cerebral leukoencephalopathy that harboured periventricular white matter hyperintensities were selected and the molecular organization of axons was determined within these regions. As in regions adjacent to lacunar infarcts, nodal and paranodal length in white matter of these patients is

  19. Tectonic geomorphology of a large normal fault: Akşehir fault, SW Turkey

    NASA Astrophysics Data System (ADS)

    Topal, Savaş; Keller, Edward; Bufe, Aaron; Koçyiğit, Ali

    2016-04-01

    In order to better understand the activity of the Akşehir normal fault in SW Turkey and the associated seismic hazard, we investigated the tectonic geomorphology of a 60-km stretch of the 100-km-long Akşehir fault block. The fault can be separated into seven geomorphic segments (1 to 7 from NW to SE) along the mountain front. Segment length varies from about 9 to 14 km, and relief of the horst block varies from about 0.6 km in the SE to 1.0 km in the NW. Analysis of the tectonic geomorphology of 32 drainage basins and mountain front facets using a combination of geomorphic indices reveals a general pattern of high slip rates in the northern and central segments and low slip rates in the southern, probably older, segments. We show that mountain front sinuosity varies from about 1.1 to 1.4 on segments S1-S6 to 2.4 on segment S7, suggesting that the six northern segments are more active than the southernmost segment. Similarly, χ analysis and slope-area analysis of streams reveal a pattern of steepest channels draining the central and northern segments of the horst. The ratio of valley floor width to valley height varies from 0.2 to 0.6, which are typical values for tectonically active mountain fronts; and alluvial fans along segments S1, S2, and S4 are back-tilted. Finally, we show that (1) shapes of the ~ 100-900m high mountain front facets are mostly triangular (~ 80%) and partly trapezoidal (~ 20%); (2) facet slopes range from 6 to 22°; (3) facets at the NW and SE segment ends are larger than the intervening facets; and (4) steepest facets occur along the central segments. Uplift rates estimated from the slope of mountain front facets range from about 0.06 m/ky on the southernmost fault segment (S7) to 0.23 m/ky on the more central S5 and 0.16 m/ky on the northern segment (S1). The estimated pattern of uplift is consistent with the pattern of geomorphic indices. The vertical relief of the facets suggests that uplift of the mountain front initiated in the late

  20. Fault Block Deformation Resulting From Fault Displacement Gradients at Yucca Mountain, Nevada

    NASA Astrophysics Data System (ADS)

    Morris, A. P.; Ferrill, D. A.; Franklin, N.; Sims, D. W.; Waiting, D. J.; Stamatakos, J. A.

    2001-12-01

    Displacement gradients on normal faults generate cutoff-line-parallel length changes. Yucca Mountain, Nevada is cut by numerous NS trending normal faults that exhibit steep displacement gradients. We apply a new method for quantifying the strain that develops adjacent to faults as a result of displacement variations, to Yucca Mountain, Nevada. Using existing maps and the Department of Energy's 3D Geologic Framework Model as sources of high precision data we have analyzed the likely state of strain of the fault blocks in Yucca Mountain. The results indicate that the strain is sensitive to the ambient stress field and the resultant slip directions at the time of fault formation, and to the orientation of the principal rock units prior to faulting. Assuming that at the time of faulting the volcanic tuffs were horizontal, and the stress field was conducive to EW-directed extension, zones of potentially high strain are identified. At least three of these are zones of intense deformation: the West Ridge connecting fault system between the Northern Windy Wash and Fatigue Wash faults, the ridges between Solitario Canyon and Fatigue Wash, and the fault block between the Iron Ridge and Solitario Canyon faults. This approach is being used to assess the intensity of deformation within fault blocks that are considered part of the Department of Energy's extended definition of blocks suitable for the U.S.A.'s potential high level nuclear waste repository. Work supported by the U.S. NRC (contract NRC-02-97-009) This work is an independent product of the CNWRA and does not necessarily represent the regulatory position of the NRC.

  1. Off-fault tip splay networks: a genetic and generic property of faults indicative of their long-term propagation, and a major component of off-fault damage

    NASA Astrophysics Data System (ADS)

    Perrin, C.; Manighetti, I.; Gaudemer, Y.

    2015-12-01

    Faults grow over the long-term by accumulating displacement and lengthening, i.e., propagating laterally. We use fault maps and fault propagation evidences available in literature to examine geometrical relations between parent faults and off-fault splays. The population includes 47 worldwide crustal faults with lengths from millimeters to thousands of kilometers and of different slip modes. We show that fault splays form adjacent to any propagating fault tip, whereas they are absent at non-propagating fault ends. Independent of parent fault length, slip mode, context, etc, tip splay networks have a similar fan shape widening in direction of long-term propagation, a similar relative length and width (~30 and ~10 % of parent fault length, respectively), and a similar range of mean angles to parent fault (10-20°). Tip splays more commonly develop on one side only of the parent fault. We infer that tip splay networks are a genetic and a generic property of faults indicative of their long-term propagation. We suggest that they represent the most recent damage off-the parent fault, formed during the most recent phase of fault lengthening. The scaling relation between parent fault length and width of tip splay network implies that damage zones enlarge as parent fault length increases. Elastic properties of host rocks might thus be modified at large distances away from a fault, up to 10% of its length. During an earthquake, a significant fraction of coseismic slip and stress is dissipated into the permanent damage zone that surrounds the causative fault. We infer that coseismic dissipation might occur away from a rupture zone as far as a distance of 10% of the length of its causative fault. Coseismic deformations and stress transfers might thus be significant in broad regions about principal rupture traces. This work has been published in Comptes Rendus Geoscience under doi:10.1016/j.crte.2015.05.002 (http://www.sciencedirect.com/science/article/pii/S1631071315000528).

  2. The microstructural character and evolution of fault rocks from the SAFOD core and potential weakening mechanisms along the San Andreas Fault (Invited)

    NASA Astrophysics Data System (ADS)

    Holdsworth, R. E.; van Diggelen, E.; Spiers, C.; de Bresser, J. H.; Smith, S. A.

    2009-12-01

    In the region of the SAFOD borehole, the San Andreas Fault (SAF) separates two very different geological terranes referred to here as the Salinian and Great Valley blocks (SB, GVB). The three sections of core preserve a diverse range of fault rocks and pass through the two currently active, highly localised slipping sections, the so-called ‘10480’ and ‘10830’ fault zones . These coincide with a broader region - perhaps as much as 100m wide - of high strain fault rocks formed at some time in the geological past, but now currently inactive. Both the slipping segments and older high strain zone(s) are developed in the GVB located NE of the terrane boundary. This is likely influenced by the phyllosilicate-rich protolith of the GVB and the large volume of trapped fluid known to exist NE and below the SAF in this region. Microstructurally, lower strain domains (most of Core 1 cutting the SB, significant parts of Core 3 cutting the GVB) preserve clear evidence for classic upper crustal cataclastic brittle faulting processes and associated fluid flow. The GVB in particular shows clear geological evidence for both fluid pressure and differential stress cycling (variable modes of hydrofacture associated with faults) during seismicity. There is also some evidence in all minor faults for the operation of limited amounts of solution-precipitation creep. High strain domains (much of Core 2 cutting the GVB, parts of Core 3 adjacent to the 10830 fault) are characterised by the development of foliated cataclasites and gouge largely due to the new growth of fine-grained phyllosilicate networks (predominantly smectite-bearing mixed layer clays, locally serpentinite, but not talc). The most deformed sections are characterised by the development of shear band fabrics and asymmetric folds. Reworking and reactivation is widespread manifested by: i) the preservation of one or more earlier generations of gouge preserved as clasts; and ii) by the development of later interconnected

  3. Fault seal analysis of Okan and Meren fields, Nigeria

    SciTech Connect

    Eisenberg, R.A.; Brenneman, R.J.; Adeogba, A.A.

    1995-08-01

    The sealing capacity and the dynamic seal behavior of faults between juxtaposed reservoirs were analyzed for Okan and Meren fields, offshore Nigeria. In both fields correlations were found between reservoir performance, juxtaposed fluid types, oil geochemistry, interpreted fluid contact relationships, fault sealing/leaking condition, and calculated smear gouge ratios. Integration of these data has been invaluable in quantifying fault seal risk and may effect depletion strategies for fault-juxtaposed reservoirs within these fields. Fault plane sections defined reservoir juxtapositions and aided visualization of potential cross-fault spill points. Smear gouge ratios calculated from E-logs were used to estimate the composition of fault-gouge materials between the juxtaposed reservoirs. These tools augmented interpretation of seal/nonseal character based on fluid contact relationships in proved reservoirs and, in addition, were used to quantify fault seal risk of untested fault-dependent closures in Okan. The results of these analyses were then used to interpret production-induced fault seal breakdown within the G-sands and also to risk seal integrity of fault dependent closures within the untested O-sands in an adjacent, upthrown fault block. Within this fault block the presence of potential fault intersection leak points and large areas of sand/sand juxtaposition with high smear gouge ratios (low sealing potential) limits potential reserves within the O-sand package. In Meren Field the E- and G-sands are juxtaposed, on different pressure decline, geochemically distinct, and are characterized by low smear gouge ratios. In contrast, specific G- and H-sands, juxtaposed across the same fault, contain similar OOWCs and are characterized by high smear gouge ratios. The cross-sealing and/or cross-leaking nature of compartment boundaries at Meren is related to fault displacement variation and the composition of displaced stratigraphy.

  4. Active fault database of Japan: Its construction and search system

    NASA Astrophysics Data System (ADS)

    Yoshioka, T.; Miyamoto, F.

    2011-12-01

    The Active fault database of Japan was constructed by the Active Fault and Earthquake Research Center, GSJ/AIST and opened to the public on the Internet from 2005 to make a probabilistic evaluation of the future faulting event and earthquake occurrence on major active faults in Japan. The database consists of three sub-database, 1) sub-database on individual site, which includes long-term slip data and paleoseismicity data with error range and reliability, 2) sub-database on details of paleoseismicity, which includes the excavated geological units and faulting event horizons with age-control, 3) sub-database on characteristics of behavioral segments, which includes the fault-length, long-term slip-rate, recurrence intervals, most-recent-event, slip per event and best-estimate of cascade earthquake. Major seismogenic faults, those are approximately the best-estimate segments of cascade earthquake, each has a length of 20 km or longer and slip-rate of 0.1m/ky or larger and is composed from about two behavioral segments in average, are included in the database. This database contains information of active faults in Japan, sorted by the concept of "behavioral segments" (McCalpin, 1996). Each fault is subdivided into 550 behavioral segments based on surface trace geometry and rupture history revealed by paleoseismic studies. Behavioral segments can be searched on the Google Maps. You can select one behavioral segment directly or search segments in a rectangle area on the map. The result of search is shown on a fixed map or the Google Maps with information of geologic and paleoseismic parameters including slip rate, slip per event, recurrence interval, and calculated rupture probability in the future. Behavioral segments can be searched also by name or combination of fault parameters. All those data are compiled from journal articles, theses, and other documents. We are currently developing a revised edition, which is based on an improved database system. More than ten

  5. The Effects of Single-Level Instrumented Lumbar Laminectomy on Adjacent Spinal Biomechanics

    PubMed Central

    Bisschop, Arno; Holewijn, Roderick M.; Kingma, Idsart; Stadhouder, Agnita; Vergroesen, Pieter-Paul A.; van der Veen, Albert J.; van Dieën, Jaap H.; van Royen, Barend J.

    2014-01-01

    Study Design Biomechanical study. Objective Posterior instrumentation is used to stabilize the spine after a lumbar laminectomy. However, the effects on the adjacent segmental stability are unknown. Therefore, we studied the range of motion (ROM) and stiffness of treated lumbar spinal segments and cranial segments after a laminectomy and after posterior instrumentation in flexion and extension (FE), lateral bending (LB), and axial rotation (AR). These outcomes might help to better understand adjacent segment disease (ASD), which is reported cranial to the level on which posterior instrumentation is applied. Methods We obtained 12 cadaveric human lumbar spines. Spines were axially loaded with 250 N for 1 hour. Thereafter, 10 consecutive load cycles (4 Nm) were applied in FE, LB, and AR. Subsequently, a laminectomy was performed either at L2 or at L4. Thereafter, load-deformation tests were repeated, after similar preloading. Finally, posterior instrumentation was added to the level treated with a laminectomy before testing was repeated. The ROM and stiffness of the treated, the cranial adjacent, and the control segments were calculated from the load-displacement data. Repeated-measures analyses of variance used the spinal level as the between-subject factor and a laminectomy or instrumentation as the within-subject factors. Results After the laminectomy, the ROM increased (+19.4%) and the stiffness decreased (−18.0%) in AR. The ROM in AR of the adjacent segments also increased (+11.0%). The ROM of treated segments after instrumentation decreased in FE (−74.3%), LB (−71.6%), and AR (−59.8%). In the adjacent segments after instrumentation, only the ROM in LB was changed (−12.9%). Conclusions The present findings do not substantiate a biomechanical pathway toward or explanation for ASD. PMID:25649753

  6. InSAR observations of strain accumulation and fault creep along the Chaman Fault system, Pakistan and Afghanistan

    NASA Astrophysics Data System (ADS)

    Fattahi, Heresh; Amelung, Falk

    2016-08-01

    We use 2004-2011 Envisat synthetic aperture radar imagery and InSAR time series methods to estimate the contemporary rates of strain accumulation in the Chaman Fault system in Pakistan and Afghanistan. At 29 N we find long-term slip rates of 16 ± 2.3 mm/yr for the Ghazaband Fault and of 8 ± 3.1 mm/yr for the Chaman Fault. This makes the Ghazaband Fault one of the most hazardous faults of the plate boundary zone. We further identify a 340 km long segment displaying aseismic surface creep along the Chaman Fault, with maximum surface creep rate of 8.1 ± 2 mm/yr. The observation that the Chaman Fault accommodates only 30% of the relative plate motion between India and Eurasia implies that the remainder is accommodated south and east of the Katawaz block microplate.

  7. 3D Dynamic Rupture Simulations Across Interacting Faults: the Mw7.0, 2010, Haiti Earthquake

    NASA Astrophysics Data System (ADS)

    Douilly, R.; Aochi, H.; Calais, E.; Freed, A. M.; Aagaard, B.

    2014-12-01

    The mechanisms controlling rupture propagation between fault segments during an earthquake are key to the hazard posed by fault systems. Rupture initiation on a fault segment sometimes transfers to a larger fault, resulting in a significant event (e.g.i, 2002 M7.9Denali and 2010 M7.1 Darfield earthquakes). In other cases rupture is constrained to the initial segment and does not transfer to nearby faults, resulting in events of moderate magnitude. This is the case of the 1989 M6.9 Loma Prieta and 2010 M7.0 Haiti earthquakes which initiated on reverse faults abutting against a major strike-slip plate boundary fault but did not propagate onto it. Here we investigatethe rupture dynamics of the Haiti earthquake, seeking to understand why rupture propagated across two segments of the Léogâne fault but did not propagate to the adjacenent Enriquillo Plantain Garden Fault, the major 200 km long plate boundary fault cutting through southern Haiti. We use a Finite Element Model to simulate the nucleation and propagation of rupture on the Léogâne fault, varying friction and background stress to determine the parameter set that best explains the observed earthquake sequence. The best-fit simulation is in remarkable agreement with several finite fault inversions and predicts ground displacement in very good agreement with geodetic and geological observations. The two slip patches inferred from finite-fault inversions are explained by the successive rupture of two fault segments oriented favorably with respect to the rupture propagation, while the geometry of the Enriquillo fault did not allow shear stress to reach failure. Although our simulation results replicate well the ground deformation consistent with the geodetic surface observation but convolving the ground motion with the soil amplification from the microzonation study will correctly account for the heterogeneity of the PGA throughout the rupture area.

  8. Minimal mass transfer across dolomitic granular fault cores

    NASA Astrophysics Data System (ADS)

    Billi, Andrea; Primavera, Paolo; Soligo, Michele; Tuccimei, Paola

    2008-01-01

    The role of chemical changes and mass transfer in the formation of granular fault cores across carbonate strata is still unclear. Thirteen granular fault cores across strata of dolostone from Sperlonga, central Italy, are analyzed by chemical and physical methods. The analyzed faults are reverse or transpressional, up to about 1 m thick, and flanked by a host rock affected by a widely developed solution cleavage. Grain size distributions of fault core rocks are determined by a sieving procedure for grains larger than 63 μm. Mechanisms of grain comminution are inferred by microscopic analyses on a set of thin sections obtained from epoxy-impregnated fault rock samples. Concentrations of calcium and magnesium in the fault cores and in the adjacent host rock are determined by titrimetry. Results show that both the breccia and the gouge forming the fault cores show little evidence for mass transfer, regardless of the fault type and grain size distribution of fault rocks. We interpret these results as chiefly the effect, within the fault core, of a strongly reduced permeability, which impeded significant mass transfer processes through solute transport. It follows that grain comminution occurred mostly by brittle processes such as crushing and abrasive wear. Previous work suggests that these results are rather generalizable; some exceptions, however, compel further research on the role of circulating fluids and mass transfer in the formation of carbonate fault rocks.

  9. Active faulting and devastating earthquakes in continental China

    NASA Astrophysics Data System (ADS)

    Zhang, P.

    2003-04-01

    The primary pattern of active tectonics in continental China is characterized by relative movements and interactions of tectonic blocks bounded by major active faults. Earthquakes are results of abrupt releases of accumulated strain energy that excesses the threshold of strength of brittle part of the earth’s crust. Boundaries of tectonic blocks are the locations of most discontinuous deformation and highest gradient of stress accumulation, thus are the most likely places for strain energy accumulation and releases, and in turn, devastating earthquakes. Almost all earthquakes of magnitude larger than 8 and 80~90% of earthquakes of magnitude over 7 occur along boundaries of active tectonic blocks. This fact indicates that differential movements and interactions of active tectonic blocks are the primary mechanism for the occurrences of devastating earthquakes. Northeastern margin of Tibetan Plateau consists of two active fault zones, the Haiyuan and the Xiangshan fault zones. Each of the zones can be further divided into several segments. Historical earthquakes during the past 800 years ruptured all of them except one segment, the so-called Tianzhu seismic gap. We have conducted paleoseismological studies on each of the segments of the fault zones. Preliminary results reveal temporal clustering features of long-term paleoearthquake activity along these two fault zones. The 1920 Haiyuan earthquake of magnitude 8.5, for example, ruptured three segments of the fault zone. We dug 19 trenches along different segments of the surface ruptures. There were 3 events along the eastern segment during the past 14000 years, 7 events along the middle segment during the past 9000 years, and 6 events along the western segment during the past 10000 years. These events clearly depict two temporal clusters. The first cluster occurs from 4600 to 6400 years, and the second occurs from 1000 to 2800 years, approximately. Each cluster lasts about 2000 years. Time period between these two

  10. Historical volcanoes of Armenia and adjacent areas: What is revisited?

    NASA Astrophysics Data System (ADS)

    Karakhanian, A.; Jrbashyan, R.; Trifonov, V.; Philip, H.; Arakelian, S.; Avagyan, A.; Baghdassaryan, H.; Davtian, V.

    2006-07-01

    The validity of some data in Karakhanian et al. [Karakhanian, A., Djrbashian, R., Trifonov V., Philip H., Arakelian S., Avagian, A., 2002. Holocene-historical volcanism and active faults as natural risk factor for Armenia and adjacent countries. Journal of Volcanology and Geothermal Research, 113, 1, 319-344; Karakhanian, A., Jrbashyan, R., Trifonov, V., Philip, H., Arakelian, S., Avagyan, A., Baghdassaryan, H., Davtian, V., Ghoukassyan, Yu., 2003. Volcanic hazards in the region of the Armenian nuclear power plant. Journal of Volcanology and Geothermal Research, 126/1-2, 31-62] that are revisited by R. Haroutiunian is considered. A conclusion is made that the revisions suggested by Haroutiunian concern unessential parts of the content of work by Karakhanian et al. [Karakhanian, A., Djrbashian, R., Trifonov V., Philip H., Arakelian S., Avagian, A., 2002. Holocene-historical volcanism and active faults as natural risk factor for Armenia and adjacent countries. Journal of Volcanology and Geothermal Research, 113, 1, 319-344; Karakhanian, A., Jrbashyan, R., Trifonov, V., Philip, H., Arakelian, S., Avagyan, A., Baghdassaryan, H., Davtian, V., Ghoukassyan, Yu., 2003. Volcanic hazards in the region of the Armenian nuclear power plant. Journal of Volcanology and Geothermal Research, 126/1-2, 31-62]. This article presents new evidence and re-proves the earlier conclusions that are disputed or revised by R. Haroutiunian.

  11. Seismic volumetric flattening and segmentation

    NASA Astrophysics Data System (ADS)

    Lomask, Jesse

    Two novel algorithms provide seismic interpretation solutions that use the full dimensionality of the data. The first is volumetric flattening and the second is image segmentation for tracking salt boundaries. Volumetric flattening is an efficient full-volume automatic dense-picking method applied to seismic data. First local dips (step-outs) are calculated over the entire seismic volume. The dips are then resolved into time shifts (or depth shifts) in a least-squares sense. To handle faults (discontinuous reflections), I apply a weighted inversion scheme. Additional information is incorporated in this flattening algorithm as geological constraints. The method is tested successfully on both synthetic and field data sets of varying degrees of complexity including salt piercements, angular unconformities, and laterally limited faults. The second full-volume interpretation method uses normalized cuts image segmentation to track salt interfaces. I apply a modified version of the normalized cuts image segmentation (NCIS) method to partition seismic images along salt interfaces. The method is capable of tracking interfaces that are not continuous, where conventional horizon tracking algorithms may fail. This method partitions the seismic image into two groups. One group is inside the salt body and the other is outside. Where the two groups meet is the salt boundary. By imposing bounds and by distributing the algorithm on a parallel cluster, I significantly increase efficiency and robustness. This method is demonstrated to be effective on both 2D and 3D seismic data sets.

  12. Oblique transfer of extensional strain between basins of the middle Rio Grande rift, New Mexico: fault kinematic and paleostress constraints

    USGS Publications Warehouse

    Minor, Scott A.; Hudson, Mark R.; Caine, Jonathan Saul; Thompson, Ren A.

    2013-01-01

    The structural geometry of transfer and accommodation zones that relay strain between extensional domains in rifted crust has been addressed in many studies over the past 30 years. However, details of the kinematics of deformation and related stress changes within these zones have received relatively little attention. In this study we conduct the first-ever systematic, multi-basin fault-slip measurement campaign within the late Cenozoic Rio Grande rift of northern New Mexico to address the mechanisms and causes of extensional strain transfer associated with a broad accommodation zone. Numerous (562) kinematic measurements were collected at fault exposures within and adjacent to the NE-trending Santo Domingo Basin accommodation zone, or relay, which structurally links the N-trending, right-stepping en echelon Albuquerque and Española rift basins. The following observations are made based on these fault measurements and paleostresses computed from them. (1) Compared to the typical northerly striking normal to normal-oblique faults in the rift basins to the north and south, normal-oblique faults are broadly distributed within two merging, NE-trending zones on the northwest and southeast sides of the Santo Domingo Basin. (2) Faults in these zones have greater dispersion of rake values and fault strikes, greater dextral strike-slip components over a wide northerly strike range, and small to moderate clockwise deflections of their tips. (3) Relative-age relations among fault surfaces and slickenlines used to compute reduced stress tensors suggest that far-field, ~E-W–trending σ3 stress trajectories were perturbed 45° to 90° clockwise into NW to N trends within the Santo Domingo zones. (4) Fault-stratigraphic age relations constrain the stress perturbations to the later stages of rifting, possibly as late as 2.7–1.1 Ma. Our fault observations and previous paleomagnetic evidence of post–2.7 Ma counterclockwise vertical-axis rotations are consistent with increased

  13. Do transform faults parallel plate motion?

    NASA Astrophysics Data System (ADS)

    Mishra, J. K.; Gordon, R. G.

    2008-12-01

    A central principle of plate tectonics is that relative plate motion is parallel to transform faults. Several workers have convincingly argued, however, that transform fault valleys widen with age due to horizontal thermal contraction of the lithosphere (Collette 1974; Roest et al 1986 ; Sandwell 1986). If so, then the transform fault zone, which is the locus of active strike-slip faulting in a transform fault, is not parallel to the direction of plate motion. It is also affected by the ridge-parallel contraction of the lithosphere and is biased by a predictable amount. Here we apply a recent model for horizontal contraction of oceanic lithosphere as a function of age (Kumar & Gordon 2008) to calculate this bias as a function of offset, spreading rate, and ridge length, with slightly different formulations for crenelate and stepping mid-ocean ridge segments. The bias causes right-slipping transform faults to be counter-clockwise of the true plate motion direction while left-slipping transform faults are clockwise of the true plate motion direction. The bias is larger for longer ridge segments, smaller offsets, and slower spreading. The bias ranges in magnitude from about 0.1 degree to 1.5 degrees for stepping boundaries and 0.2 degree to 3 degrees for crenelate boundaries. Application of the bias correction to NUVEL-1 transform fault azimuths about the Rodrigues, Juan Fernandez, Galapagos, and Bouvet triple junctions improves the closure of the triple junction in the first three cases but makes it slightly worse in the fourth case. Additional applications will be presented.

  14. Complex Faulting within the New Madrid Seismic Zone

    NASA Astrophysics Data System (ADS)

    Deshon, H. R.; Powell, C. A.; Magnani, M.; Bisrat, S. T.

    2010-12-01

    Relative relocations derived using double-difference tomography techniques reveal a complex sequence of faulting within the New Madrid Seismic Zone (NMSZ) and upper Mississippi Embayment. The majority of NMSZ seismicity recorded over the last 30 years occurs along four limbs: 1) a NE-SW trending dextral strike-slip fault, termed the Axial fault, coincident with the central valley of the Cambrian Reelfoot Rift system; 2) the SE-NW trending Reelfoot thrust fault; 3) a E-W trending left lateral strike-slip fault extending off of the northern terminus of the Reelfoot fault, here termed New Madrid west; and 4) a NE-SW dextral strike-slip fault also extending off of the northern terminus of the Reelfoot fault, here termed New Madrid north. Each of these segments is thought to have ruptured during the 1811-1812 large earthquake sequence. A fifth segment, the Bootheel lineament, is marked by 1811-1812 related liquefaction features but appears largely aseismic, though we suggest there are at least five events in the catalog associated with this feature. Geological and geophysical evidence across the embayment suggests that the region is crossed by additional faults at shallow depths (<1-2 km), while seismicity is generally confined to the 3-20 km depth range. Here we present relative relocations derived using catalog and waveform cross-correlation differential times of the 1989-1992 local PANDA network and the 1995-2010 Cooperative New Madrid Seismic Network. We show that the four known seismic lineations exhibit internal complexity. For example, New Madrid north is composed of two parallel faults rather then a single fault, and seismicity associated with the Axial lineation exhibits temporal changes along strike and becomes spatially more diffuse south of the Axial fault/Bootheel lineament intersection. Seismicity along the southern Reelfoot fault does not define a dipping plane consistent with thrust faulting, unlike the northern Reelfoot fault, and is associated with

  15. Aftershocks of the 2014 South Napa, California, Earthquake: Complex faulting on secondary faults

    USGS Publications Warehouse

    Hardebeck, Jeanne L.; Shelly, David R.

    2016-01-01

    We investigate the aftershock sequence of the 2014 MW6.0 South Napa, California, earthquake. Low-magnitude aftershocks missing from the network catalog are detected by applying a matched-filter approach to continuous seismic data, with the catalog earthquakes serving as the waveform templates. We measure precise differential arrival times between events, which we use for double-difference event relocation in a 3D seismic velocity model. Most aftershocks are deeper than the mainshock slip, and most occur west of the mapped surface rupture. While the mainshock coseismic and postseismic slip appears to have occurred on the near-vertical, strike-slip West Napa fault, many of the aftershocks occur in a complex zone of secondary faulting. Earthquake locations in the main aftershock zone, near the mainshock hypocenter, delineate multiple dipping secondary faults. Composite focal mechanisms indicate strike-slip and oblique-reverse faulting on the secondary features. The secondary faults were moved towards failure by Coulomb stress changes from the mainshock slip. Clusters of aftershocks north and south of the main aftershock zone exhibit vertical strike-slip faulting more consistent with the West Napa Fault. The northern aftershocks correspond to the area of largest mainshock coseismic slip, while the main aftershock zone is adjacent to the fault area that has primarily slipped postseismically. Unlike most creeping faults, the zone of postseismic slip does not appear to contain embedded stick-slip patches that would have produced on-fault aftershocks. The lack of stick-slip patches along this portion of the fault may contribute to the low productivity of the South Napa aftershock sequence.

  16. Segmental neuromyotonia

    PubMed Central

    Panwar, Ajay; Junewar, Vivek; Sahu, Ritesh; Shukla, Rakesh

    2015-01-01

    Unilateral focal neuromyotonia has been rarely reported in fingers or extraocular muscles. We report a case of segmental neuromyotonia in a 20-year-old boy who presented to us with intermittent tightness in right upper limb. Electromyography revealed myokymic and neuromyotonic discharges in proximal as well as distal muscles of the right upper limb. Patient's symptoms responded well to phenytoin therapy. Such an atypical involvement of two contiguous areas of a single limb in neuromyotonia has not been reported previously. Awareness of such an atypical presentation of the disease can be important in timely diagnosis and treatment of a patient. PMID:26167035

  17. Geodynamics of the Dead Sea Fault: Do active faulting and past earthquakes determine the seismic gaps?

    NASA Astrophysics Data System (ADS)

    Meghraoui, Mustapha

    2014-05-01

    The ~1000-km-long North-South trending Dead Sea transform fault (DSF) presents structural discontinuities and includes segments that experienced large earthquakes (Mw>7) in historical times. The Wadi Araba and Jordan Valley, the Lebanese restraining bend, the Missyaf and Ghab fault segments in Syria and the Ziyaret Fault segment in Turkey display geometrical complexities made of step overs, restraining and releasing bends that may constitute major obstacles to earthquake rupture propagation. Using active tectonics, GPS measurements and paleoseismology we investigate the kinematics and long-term/short term slip rates along the DSF. Tectonic geomorphology with paleoseismic trenching and archeoseismic investigations indicate repeated faulting events and left-lateral slip rate ranging from 4 mm/yr in the southern fault section to 6 mm/yr in the northern fault section. Except for the northernmost DSF section, these estimates of fault slip rate are consistent with GPS measurements that show 4 to 5 mm/yr deformation rate across the plate boundary. However, recent GPS results showing ~2.5 mm/yr velocity rate of the northern DSF appears to be quite different than the ~6 mm/yr paleoseismic slip rate. The kinematic modeling that combines GPS and seismotectonic results implies a complex geodynamic pattern where the DSF transforms the Cyprus arc subduction zone into transpressive tectonics on the East Anatolian fault. The timing of past earthquake ruptures shows the occurrence of seismic sequences and a southward migration of large earthquakes, with the existence of major seismic gaps along strike. In this paper, we discuss the role of the DSF in the regional geodynamics and its implication on the identification of seismic gaps.

  18. Strike-slip fault propagation and linkage via work optimization with application to the San Jacinto fault, California

    NASA Astrophysics Data System (ADS)

    Madden, E. H.; McBeck, J.; Cooke, M. L.

    2013-12-01

    Over multiple earthquake cycles, strike-slip faults link to form through-going structures, as demonstrated by the continuous nature of the mature San Andreas fault system in California relative to the younger and more segmented San Jacinto fault system nearby. Despite its immaturity, the San Jacinto system accommodates between one third and one half of the slip along the boundary between the North American and Pacific plates. It therefore poses a significant seismic threat to southern California. Better understanding of how the San Jacinto system has evolved over geologic time and of current interactions between faults within the system is critical to assessing this seismic hazard accurately. Numerical models are well suited to simulating kilometer-scale processes, but models of fault system development are challenged by the multiple physical mechanisms involved. For example, laboratory experiments on brittle materials show that faults propagate and eventually join (hard-linkage) by both opening-mode and shear failure. In addition, faults interact prior to linkage through stress transfer (soft-linkage). The new algorithm GROW (GRowth by Optimization of Work) accounts for this complex array of behaviors by taking a global approach to fault propagation while adhering to the principals of linear elastic fracture mechanics. This makes GROW a powerful tool for studying fault interactions and fault system development over geologic time. In GROW, faults evolve to minimize the work (or energy) expended during deformation, thereby maximizing the mechanical efficiency of the entire system. Furthermore, the incorporation of both static and dynamic friction allows GROW models to capture fault slip and fault propagation in single earthquakes as well as over consecutive earthquake cycles. GROW models with idealized faults reveal that the initial fault spacing and the applied stress orientation control fault linkage propensity and linkage patterns. These models allow the gains in

  19. The effect of porosity on fault slip mechanisms at East Pacific Rise transform faults: insight from observations and models at the Gofar Fault (Invited)

    NASA Astrophysics Data System (ADS)

    Roland, E. C.; McGuire, J. J.; Lizarralde, D.; Behn, M. D.; Collins, J. A.

    2013-12-01

    In this study, we combine recent local observations and numerical models to show that Pacific oceanic transform faults contain consistent high-porosity damage zones that extend throughout the crust within localized regions along the fault. Heterogeneity in fault zone material properties associated with along-strike changes in porosity and fluid-related effects may promote variations in fault-slip mechanisms, with slow, aseismic slip in some fault segments and fast, seismic rupture in others. Ocean bottom seismometer observations made during the 2008 rupture process of the Gofar fault (4° S on the East Pacific Rise), in combination with ~25 years of teleseismic observations, indicate significant along-strike variability in fault slip mechanisms; discrete fault segments fail regularly in Mw 6.0 earthquakes, and seismogenic segments are separated by velocity-strengthening, ~10-km-long rupture barriers that appear to fail during earthquake swarms, likely accompanied by aseismic slip. 3D models of the Gofar fault thermal structure suggest that swarm microearthquake hypocenters within the rupture barrier zones occur at depths greater than would be expected to sustain brittle failure, and at temperatures too hot to exhibit stick-slip behavior in lower crust and upper mantle rocks. This observation suggests that some mechanism leads to enhanced cooling within discrete zones along the fault. The seismic structure of the Gofar rupture barrier region is imaged using P-wave traveltime tomography as a ~2-km-wide low velocity zone that extends through the entire crust. Reduced velocities can be explained if the plate-boundary region is composed of fault material with enhanced fluid-filled porosity (1.5-8%). Enhanced porosity, and associated increased hydrothermal heat transport deep within the crust at Gofar is also consistent with the observed deep seismicity and apparently cooler fault structure in distinct fault segments. Dilatency strengthening is one mechanism that may be

  20. Metamorphism, argon depletion, heat flow and stress on the Alpine fault

    NASA Technical Reports Server (NTRS)

    Scholz, C. H.; Beavan, J.; Hanks, T. C.

    1978-01-01

    The Alpine fault of New Zealand is a major continental transform fault which was uplifted on its southeast side 4 to 11 km within the last 5 m.y. This uplift has exposed the Haast schists, which were metamorphosed from the adjacent Torlesse graywackes. The Haast schists increase in metamorphic grade from prehnite-pumpellyite facies 9-12 km from the fault through the chlorite and biotite zones of the greenschist facies to the garnet-oligoclase zone amphibolite facies within 4 km of the fault. These metamorphic zone boundaries are subparallel to the fault for 350 km along the strike. The K-Ar and Rb-Sr ages of the schists increase with distance from the fault: from 4 m.y. within 3 km of the fault to approximately 110 m.y. 20 km from the fault. Field relations show that the source of heat that produced the argon depletion aureole was the fault itself.

  1. Anatomy of a Plate Boundary at Shallow Crustal Levels: a Composite Section from the Alpine Fault, New Zealand

    NASA Astrophysics Data System (ADS)

    Barth, N. C.; Toy, V. G.; Boulton, C. J.; Carpenter, B. M.

    2010-12-01

    New Zealand's Alpine Fault is mostly a moderately SE-dipping dextral reverse plate boundary structure, but at its southern end, strike-slip-normal motion is indicated by offset of recent surfaces, juxtaposition of sediments, and both brittle and ductile shear sense indicators. At the location of uplift polarity reversal fault rocks exhumed from both the hangingwall Pacific and footwall Australian Plates are juxtaposed, offering a remarkably complete cross section of the plate boundary at shallow crustal levels. We describe Alpine Fault damage zone and fault core structures overprinted on Pacific and Australian plate mylonites of a variety of compositions, in a fault-strike perpendicular composite section spanning the reversal in dip-slip polarity. The damage zone is asymmetric; on the Australian Plate 160m of quartzose paragneiss-derived mylonites are overprinted by brittle faults and fractures that increase in density towards the principal slip surface (PSS). This damage zone fabric consists of 1-10m-spaced, moderately to steeply-dipping, 1-20cm-thick gouge-filled faults, overprinted on and sub-parallel to a mylonitic foliation sub-parallel to the PSS. On the Pacific Plate, only 40m of the 330m section of volcaniclastic-derived mylonites have brittle damage in the form of unhealed fractures and faults, as well as a pervasive greenschist facies hydrothermal alteration absent in the footwall. These damage-related structures comprise a network of small-offset faults and fractures with increasing density and intensity towards the PSS. The active Pacific Plate fault core is composed of ~1m of cataclasite grading into folded protocataclasite that is less folded and fractured with increasing distance from the PSS. The active Australian Plate fault core is <1.5m wide and consists of 3 distinct foliated clay gouges, as well as a 4cm thick brittle ultracataclasite immediately adjacent to the active PSS. The Australian Plate foliated clay gouge contains stringers of quartz

  2. Identification and interpretation of tectonic features from ERTS-1 imagery. [geological faults in California mountain regions

    NASA Technical Reports Server (NTRS)

    Abdel-Gawad, M. (Principal Investigator)

    1974-01-01

    The author has identified the following significant results. ERTS-1 imagery shows that the southern segment of the San Gabriel fault which controls the west fork of the San Gabriel River is strikingly similar to the Mill Creek Fault in the San Bernardino Mountains. It has also been noted that there is a similarity between the Sierra Madre thrust zone of the San Gabriel Mountains to the Banning thrust of the San Bernardino Mountains. This suggests that the southern San Gabriel fault was once continuous with the Mill Creek fault. When the San Bernardino Mountain block is theoretically moved to the northwest along the San Jacinto fault so that the Mill Creek fault is aligned with the southern part of the San Gabriel fault, it was found that the four transverse fault segments become aligned with the Pinto Fault on the east and with the Raymond-Santa Monica Malibu Fault zone on the west. The reconstruction identifies a continuous zone of transverse faulting extending from the Colorado River Desert to the Pacific. It seems likely that the entire fault zone was once a continuous left-lateral shear. This Anacapa Shear has probably been subjected to a 50 km left lateral movement. This analysis strongly indicates that the tectonic history of the Transverse Range has been characterized by left lateral shear on transverse faults and right lateral shear on the San Andreas fault system.

  3. Tectonic geomorphology and neotectonics of the Kyaukkyan Fault, Myanmar

    NASA Astrophysics Data System (ADS)

    Crosetto, Silvia; Watkinson, Ian; Gori, Stefano; Falcucci, Emanuela; Min, Soe

    2016-04-01

    The Kyaukkyan Fault is a dextral strike-slip fault, part of a complex zone of active dextral transpression that absorbs most of the northward motion of India relative to Sundaland. While much of the strike-slip displacement is localised in western Myanmar and along the prominent Sagaing Fault, significant dextral shear also occurs across the Kyaukkyan Fault, on the Shan Plateau in the east. The largest recorded earthquake in Myanmar occurred on the Kyaukkyan Fault in 1912, near Maymyo (Mw 7.7), but the fault has generated little significant seismicity since then. Despite its demonstrated seismic potential and remarkable topographic expression, the fault's neotectonic history remains poorly known. Interpretation of ≤30 m Landsat TM/ETM+ images, together with field investigations, reveals deformation features developed along the Kyaukkyan Fault system, mostly indicative of Quaternary dextral strike-slip faulting. Well-marked fault scarps and valleys locate the fault especially in its northernmost and southernmost part; geomorphic features related with Kyaukkyan Fault activity are sag ponds, shutter ridges, offset and beheaded streams, triangular facets and low-sinuosity mountain fronts. Geomorphic markers of young fault activity such as offset and deformed alluvial fans, wind-gaps were also identified during field observation. The fault's central section is characterised by a complex pull-apart system, whose normal border faults show signals of relatively slow neotectonic activity. In the central part of the basin, deformation of Quaternary sediments by a locally-buried cross-basin fault system includes dip-slip faulting, where subsidence adjacent to linear ridges is suggested by notably active mountain fronts, dextral strike-slip faulting and local transpression. Although no direct evidence of a 1912 surface rupture has been detected, the fresh geomorphic expression of the cross-basin fault system indicates that it is likely to have been the focus of that event

  4. Fault-Zone Maturity Defines Maximum Earthquake Magnitude: The case of the North Anatolian Fault Zone

    NASA Astrophysics Data System (ADS)

    Bohnhoff, Marco; Bulut, Fatih; Stierle, Eva; Martinez-Garzon, Patricia; Benzion, Yehuda

    2015-04-01

    Estimating the maximum likely magnitude of future earthquakes on transform faults near large metropolitan areas has fundamental consequences for the expected hazard. Here we show that the maximum earthquakes on different sections of the North Anatolian Fault Zone (NAFZ) scale with the duration of fault zone activity, cumulative offset and length of individual fault segments. The findings are based on a compiled catalogue of historical earthquakes in the region, using the extensive literary sources that exist due to the long civilization record. We find that the largest earthquakes (M~8) are exclusively observed along the well-developed part of the fault zone in the east. In contrast, the western part is still in a juvenile or transitional stage with historical earthquakes not exceeding M=7.4. This limits the current seismic hazard to NW Turkey and its largest regional population and economical center Istanbul. Our findings for the NAFZ are consistent with data from the two other major transform faults, the San Andreas fault in California and the Dead Sea Transform in the Middle East. The results indicate that maximum earthquake magnitudes generally scale with fault-zone evolution.

  5. Fault zone structure from topography: signatures of en echelon fault slip at Mustang Ridge on the San Andreas Fault, Monterey County, California

    USGS Publications Warehouse

    DeLong, Stephen B.; Hilley, George E.; Rymer, Michael J.; Prentice, Carol

    2010-01-01

    We used high-resolution topography to quantify the spatial distribution of scarps, linear valleys, topographic sinks, and oversteepened stream channels formed along an extensional step over on the San Andreas Fault (SAF) at Mustang Ridge, California. This location provides detail of both creeping fault landform development and complex fault zone kinematics. Here, the SAF creeps 10–14 mm/yr slower than at locations ∼20 km along the fault in either direction. This spatial change in creep rate is coincident with a series of en echelon oblique-normal faults that strike obliquely to the SAF and may accommodate the missing deformation. This study presents a suite of analyses that are helpful for proper mapping of faults in locations where high-resolution topographic data are available. Furthermore, our analyses indicate that two large subsidiary faults near the center of the step over zone appear to carry significant distributed deformation based on their large apparent vertical offsets, the presence of associated sag ponds and fluvial knickpoints, and the observation that they are rotating a segment of the main SAF. Several subsidiary faults in the southeastern portion of Mustang Ridge are likely less active; they have few associated sag ponds and have older scarp morphologic ages and subdued channel knickpoints. Several faults in the northwestern part of Mustang Ridge, though relatively small, are likely also actively accommodating active fault slip based on their young morphologic ages and the presence of associated sag ponds.

  6. Deriving structure from evolution: metazoan segmentation.

    PubMed

    François, Paul; Hakim, Vincent; Siggia, Eric D

    2007-01-01

    Segmentation is a common feature of disparate clades of metazoans, and its evolution is a central problem of evolutionary developmental biology. We evolved in silico regulatory networks by a mutation/selection process that just rewards the number of segment boundaries. For segmentation controlled by a static gradient, as in long-germ band insects, a cascade of adjacent repressors reminiscent of gap genes evolves. For sequential segmentation controlled by a moving gradient, similar to vertebrate somitogenesis, we invariably observe a very constrained evolutionary path or funnel. The evolved state is a cell autonomous 'clock and wavefront' model, with the new attribute of a separate bistable system driven by an autonomous clock. Early stages in the evolution of both modes of segmentation are functionally similar, and simulations suggest a possible path for their interconversion. Our computation illustrates how complex traits can evolve by the incremental addition of new functions on top of pre-existing traits.

  7. Hierarchical Image Segmentation Using Correlation Clustering.

    PubMed

    Alush, Amir; Goldberger, Jacob

    2016-06-01

    In this paper, we apply efficient implementations of integer linear programming to the problem of image segmentation. The image is first grouped into superpixels and then local information is extracted for each pair of spatially adjacent superpixels. Given local scores on a map of several hundred superpixels, we use correlation clustering to find the global segmentation that is most consistent with the local evidence. We show that, although correlation clustering is known to be NP-hard, finding the exact global solution is still feasible by breaking the segmentation problem down into subproblems. Each such sub-problem can be viewed as an automatically detected image part. We can further accelerate the process by using the cutting-plane method, which provides a hierarchical structure of the segmentations. The efficiency and improved performance of the proposed method is compared to several state-of-the-art methods and demonstrated on several standard segmentation data sets.

  8. Faulted Ancient Aqueduct and Successive Displacements along the Dead Sea Fault in Syria

    NASA Astrophysics Data System (ADS)

    Sbeinat, R.; Meghraoui, M.; Gomez, F.; van der Woerd, J.; Layyous, I.; Al-Ghazzi, R.; Barazangi, M.

    2003-04-01

    We conducted a combined study in archeoseismology with detailed descriptions and mapping with a total station of a faulted ancient aqueduct, and in paleoseismology with a 15-m-long and 3.5-m-deep trench near the aqueduct and across the fault. Micro-topographic surveys and trenching show that the fault offsets left-laterally an ancient aqueduct which is repeatedly fractured and younger than BC 410. Projecting the aqueduct walls into the north-south striking DSF displays a total left-lateral displacement of 13.6 ±0.2 m between the two blocks of the faulted aqueduct. Moreover, the northern warped wall shows a deflection (with cracks and brecciated travertines below) that amount 4.3 m and can be considered as a minimum for the first left-lateral displacement. The aqueduct also displays at least two kinds of building stones suggesting rebuilding episodes. Using radiocarbon dating of faulted young alluvial deposits we document the occurrence of three large earthquakes in the past 2200 years (between BC 150 - AD 750, between AD 700 - 1030 and between AD 990 - 1210). The most recent faulting event may correspond to the well-documented large earthquake of AD 1170 for which we estimate Mw = 7.3 - 7.5. Our study provides the timing of late Holocene earthquakes and constrains the 6.9 ± 1.2 mm/yr. slip rate of the Dead Sea transform fault in northwestern Syria (the Missyaf fault segment). Reports of large earthquakes and their associated damage in the Middle East are frequently reported during the Greek, Hebrew, Assyrian, Roman, Byzantine and Islamic times. The ˜830 years of seismic quiescence along the Missyaf fault segment implies that a large earthquake is overdue and may result in a major catastrophe to the population centres of Syria and Lebanon.

  9. Large-scale Geometry of Intra-continental Strike-slip Faults: Example of the Karakorum Fault, Western Tibet

    NASA Astrophysics Data System (ADS)

    Chevalier, M. L.; Leloup, P. H.; Li, H.

    2015-12-01

    How large-scale, active strike-slip fault systems are defined can sometimes be ambiguous, especially when viewed at different timescales (geodetic vs longer term measurements). Does every kilometer of the fault system need to be visible in the morphology (offset geomorphic features, fault trace, etc) to be considered as currently active? Does every segment of the fault need to have a unique and consistent kinematics along the entire fault system (normal, strike-slip, reverse)? Does all segments need to be physically connected at the surface to be considered part of the same fault system? To illustrate our arguments against such statements, we use the example of the right-lateral strike-slip Karakorum fault, located in western Tibet, along which lively debates have been taking place in the last ~20 years. These concern its initiation age, total geologic offsets, slip-rates, and more recently, even the location and current activity of the northern half of the fault. In particular, whether the active Kongur Shan extensional system, located in the Chinese Pamir, belongs to the Karakorum fault system remains controversial. Here, we argue that both systems are connected and that they both play a significant role in accommodating deformation at the western Himalayan syntaxis, under the form of extensional displacement in the Chinese Pamir.

  10. Structural evolution of fault zones in sandstone by multiple deformation mechanisms: Moab fault, southeast Utah

    USGS Publications Warehouse

    Davatzes, N.C.; Eichhubl, P.; Aydin, A.

    2005-01-01

    Faults in sandstone are frequently composed of two classes of structures: (1) deformation bands and (2) joints and sheared joints. Whereas the former structures are associated with cataclastic deformation, the latter ones represent brittle fracturing, fragmentation, and brecciation. We investigated the distribution of these structures, their formation, and the underlying mechanical controls for their occurrence along the Moab normal fault in southeastern Utah through the use of structural mapping and numerical elastic boundary element modeling. We found that deformation bands occur everywhere along the fault, but with increased density in contractional relays. Joints and sheared joints only occur at intersections and extensional relays. In all locations , joints consistently overprint deformation bands. Localization of joints and sheared joints in extensional relays suggests that their distribution is controlled by local variations in stress state that are due to mechanical interaction between the fault segments. This interpretation is consistent with elastic boundary element models that predict a local reduction in mean stress and least compressive principal stress at intersections and extensional relays. The transition from deformation band to joint formation along these sections of the fault system likely resulted from the combined effects of changes in remote tectonic loading, burial depth, fluid pressure, and rock properties. In the case of the Moab fault, we conclude that the structural heterogeneity in the fault zone is systematically related to the geometric evolution of the fault, the local state of stress associated with fault slip , and the remote loading history. Because the type and distribution of structures affect fault permeability and strength, our results predict systematic variations in these parameters with fault evolution. ?? 2004 Geological Society of America.

  11. Seismic measurements of the internal properties of fault zones

    USGS Publications Warehouse

    Mooney, W.D.; Ginzburg, A.

    1986-01-01

    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. ?? 1986 Birkha??user Verlag, Basel.

  12. The magnitude distribution of earthquakes near Southern California faults

    USGS Publications Warehouse

    Page, M.T.; Alderson, D.; Doyle, J.

    2011-01-01

    We investigate seismicity near faults in the Southern California Earthquake Center Community Fault Model. We search for anomalously large events that might be signs of a characteristic earthquake distribution. We find that seismicity near major fault zones in Southern California is well modeled by a Gutenberg-Richter distribution, with no evidence of characteristic earthquakes within the resolution limits of the modern instrumental catalog. However, the b value of the locally observed magnitude distribution is found to depend on distance to the nearest mapped fault segment, which suggests that earthquakes nucleating near major faults are likely to have larger magnitudes relative to earthquakes nucleating far from major faults. Copyright 2011 by the American Geophysical Union.

  13. Nonlinear Network Dynamics on Earthquake Fault Systems

    NASA Astrophysics Data System (ADS)

    Rundle, P. B.; Rundle, J. B.; Tiampo, K. F.

    2001-12-01

    Understanding the physics of earthquakes is essential if large events are ever to be forecast. Real faults occur in topologically complex networks that exhibit cooperative, emergent space-time behavior that includes precursory quiescence or activation, and clustering of events. The purpose of this work is to investigate the sensitivity of emergent behavior of fault networks to changes in the physics on the scale of single faults or smaller. In order to investigate the effect of changes at small scales on the behavior of the network, we need to construct models of earthquake fault systems that contain the essential physics. A network topology is therefore defined in an elastic medium, the stress Green's functions (i.e. the stress transfer coefficients) are computed, frictional properties are defined and the system is driven via the slip deficit as defined below. The long-range elastic interactions produce mean-field dynamics in the simulations. We focus in this work on the major strike-slip faults in Southern California that produce the most frequent and largest magnitude events. To determine the topology and properties of the network, we used the tabulation of fault properties published in the literature. We have found that the statistical distribution of large earthquakes on a model of a topologically complex, strongly correlated real fault network is highly sensitive to the precise nature of the stress dissipation properties of the friction laws associated with individual faults. These emergent, self-organizing space-time modes of behavior are properties of the network as a whole, rather than of the individual fault segments of which the network is comprised (ref: PBR et al., Physical Review Letters, in press, 2001).

  14. Onset and Mechanisms of Surface Creep on Strike Slip Faults: Clues from the North Anatolian Fault and Comparisons with the San Andreas Fault

    NASA Astrophysics Data System (ADS)

    Cakir, Z.; Ergintav, S.; Akoglu, A. M.; Cetin, E.; Meghraoui, M.; Reilinger, R. E.

    2014-12-01

    Aseismic fault slip was first reported over forty years ago along some major strike slip faults including the San Andreas (SAF) and North Anatolian faults (NAF). Yet both their origin and timing on active faults and underlying physical processes remain subjects of debate. The presence of weak minerals and/or trapped fluid overpressures within fault zones have been proposed as mechanics for aseismic fault creep. Our InSAR observations together with GPS measurements and geology along the NAF provide new evidence for the mechanism, characteristics, and initiation of fault surface creep. We have used the persistent scatterer InSAR (PS-InSAR) technique to investigate both the creeping section of the NAF at Ismetpaşa that had ruptured during the 1944 and 1951 earthquakes, and the postseismic era of the 1999 İzmit Earthquake. The results reveal that the central segment of the 1999 Izmit Earthquake rupture has been creeping for over for the past 15 years since the event, becoming the longest lasting afterslip ever recorded. The slip pattern of ongoing surface creep on the İzmit rupture supports the idea that stable fault creep can be initiated as postseismic afterslip, a mechanism we proposed previously but could not have confirmed due to the lack of pre- and post-earthquake observations on creeping faults such as the Ismetpaşa segment of the NAF and the segments of the SAF in the San Francisco Bay area. Geological maps along the Ismetpaşa and Izmit creeping segments show that both fault zones run through ophiolitic and calcareous rocks with phyllosilicates that probably result in fault weakening. Earthquake rupture maps and PS-InSAR velocity fields for these regions also reveal that the creeping faults have simple geometry being fairly rectilinear and continuous along their strike. These common features suggest that following a large earthquake, a stable surface creep can be triggered on a section of a mature fault if it has evolved in to simple geometry and is

  15. Triggered aseismic slip adjacent to the 6 February 2013 Mw 8.0 Santa Cruz Islands megathrust earthquake

    USGS Publications Warehouse

    Hayes, Gavin P.; Furlong, Kevin P.; Benz, Harley M.; Herman, Matthew W.

    2014-01-01

    Aseismic or slow slip events have been observed in many subduction zones, but whether they affect the occurrence of earthquakes or result from stress changes caused by nearby events is unclear. In an area lacking direct geodetic observations, inferences can be made from seismological studies of co-seismic slip, associated stress changes and the spatiotemporal nature of aftershocks. These observations indicate that the February 2013 Mw 8.0 Santa Cruz Islands earthquake may have triggered slow or aseismic slip on an adjacent section of the subduction thrust over the following hours to days. This aseismic event was equivalent to Mw 7.6, significantly larger than any earthquakes in the aftershock sequence. The aseismic slip was situated within the seismogenic portion of the subduction interface, and must have occurred to the south of the main seismic slip and most aftershocks in order to promote right-lateral faulting in the upper plate, the dominant deformation style of the aftershock sequence. This plate boundary segment can support either stable sliding (aseismic) or stick-slip (seismic) deformation in response to different driving conditions. The complete lack of aftershocks on the thrust interface implies this pair of megathrust slip episodes (seismic and aseismic) released a substantial portion of the stored strain on the northernmost section of the Vanuatu subduction zone.

  16. Triggered aseismic slip adjacent to the 6 February 2013 Mw 8.0 Santa Cruz Islands megathrust earthquake

    NASA Astrophysics Data System (ADS)

    Hayes, Gavin P.; Furlong, Kevin P.; Benz, Harley M.; Herman, Matthew W.

    2014-02-01

    Aseismic or slow slip events have been observed in many subduction zones, but whether they affect the occurrence of earthquakes or result from stress changes caused by nearby events is unclear. In an area lacking direct geodetic observations, inferences can be made from seismological studies of co-seismic slip, associated stress changes and the spatiotemporal nature of aftershocks. These observations indicate that the February 2013 Mw 8.0 Santa Cruz Islands earthquake may have triggered slow or aseismic slip on an adjacent section of the subduction thrust over the following hours to days. This aseismic event was equivalent to Mw 7.6, significantly larger than any earthquakes in the aftershock sequence. The aseismic slip was situated within the seismogenic portion of the subduction interface, and must have occurred to the south of the main seismic slip and most aftershocks in order to promote right-lateral faulting in the upper plate, the dominant deformation style of the aftershock sequence. This plate boundary segment can support either stable sliding (aseismic) or stick-slip (seismic) deformation in response to different driving conditions. The complete lack of aftershocks on the thrust interface implies this pair of megathrust slip episodes (seismic and aseismic) released a substantial portion of the stored strain on the northernmost section of the Vanuatu subduction zone.

  17. Earthquake Probabilities and Magnitude Distribution in 100a along the Haiyuan Fault, northwestern China

    NASA Astrophysics Data System (ADS)

    Ran, H.

    2004-12-01

    The Haiyuan fault is a major seismogenic fault in north-central China. One of the most devastating great earthquake in 20th century occurred near Haiyuan in northwestern China in December 16, 1920. More than 220000 people were killed and thousands of towns and villages were destroyed during this devastating earthquake. A 230 km long left-lateral surface rupture zone formed along the Haiyuan fault during the earthquake with maximum left lateral displacement of 10 m. In recent years, some researchers have studied the paleoseismology along the Haiyuan fault and revealed a lot of paleoearthquake events. All available information allows more reliable analysis of earthquake recurrence interval and earthquake rupture patterns along the Haiyuan fault. Based on fault geometry, segmentation pattern, and paleoearthquake events along the Haiyuan fault we can identify three scales of earthquake rupture: rupture of one segment, cascade rupture of two segments, and cascade rupture of entire fault (three segments), and obtain the earthquake recurrence intervals of these scales of earthquake rupture. The earthquake probability and magnitude distribution in 100-year along the Haiyuan fault can be obtained through weighted computation, by applying these paleoseismological information mentioned above, using Possion and Brownian passage time model and considering different rupture patterns. The result shows that the earthquakes probability of is about 0.035 in 100-year along the Haiyuan fault.

  18. The Morelia-Acambay Fault System

    NASA Astrophysics Data System (ADS)

    Velázquez Bucio, M.; Soria-Caballero, D.; Garduño-Monroy, V.; Mennella, L.

    2013-05-01

    The Trans-Mexican Volcanic Belt (TMVB) is one of the most actives and representative zones of Mexico geologically speaking. Research carried out in this area gives stratigraphic, seismologic and historical evidence of its recent activity during the quaternary (Martinez and Nieto, 1990). Specifically the Morelia-Acambay faults system (MAFS) consist in a series of normal faults of dominant direction E - W, ENE - WSW y NE - SW which is cut in center west of the Trans-Mexican Volcanic Belt. This fault system appeared during the early Miocene although the north-south oriented structures are older and have been related to the activity of the tectonism inherited from the "Basin and Range" system, but that were reactivated by the east- west faults. It is believed that the activity of these faults has contributed to the creation and evolution of the longed lacustrine depressions such as: Chapala, Zacapu, Cuitzeo, Maravatio y Acambay also the location of monogenetic volcanoes that conformed the Michoacan-Guanajuato volcanic field (MGVF) and tend to align in the direction of the SFMA dominant effort. In a historical time different segments of the MAFS have been the epicenter of earthquakes from moderated to strong magnitude like the events of 1858 in Patzcuaro, Acambay in 1912, 1979 in Maravatio and 2007 in Morelia, among others. Several detailed analysis and semi-detailed analysis through a GIS platform based in the vectorial archives and thematic charts 1:50 000 scaled from the data base of the INEGI which has allowed to remark the influence of the MAFS segments about the morphology of the landscape and the identification of other structures related to the movement of the existent faults like fractures, alignments, collapses and others from the zone comprehended by the northwest of Morelia in Michoacán to the East of Acambay, Estado de México. Such analysis suggests that the fault segments possess a normal displacement plus a left component. In addition it can be

  19. Magmatic and tectonic extension at the Chile Ridge: Evidence for mantle controls on ridge segmentation

    NASA Astrophysics Data System (ADS)

    Howell, Samuel M.; Ito, Garrett; Behn, Mark D.; Martinez, Fernando; Olive, Jean-Arthur; Escartín, Javier

    2016-06-01

    We use data from an extensive multibeam bathymetry survey of the Chile Ridge to study tectonomagmatic processes at the ridge axis. Specifically, we investigate how abyssal hills evolve from axial faults, how variations in magmatic extension influence morphology and faulting along the spreading axis, and how these variations correlate with ridge segmentation. The bathymetry data are used to estimate the fraction of plate separation accommodated by normal faulting, and the remaining fraction of extension, M, is attributed primarily to magmatic accretion. Results show that M ranges from 0.85 to 0.96, systematically increasing from first-order and second-order ridge segment offsets toward segment centers as the depth of ridge axis shoals relative to the flanking highs of the axial valley. Fault spacing, however, does not correlate with ridge geometry, morphology, or M along the Chile Ridge, which suggests the observed increase in tectonic strain toward segment ends is achieved through increased slip on approximately equally spaced faults. Variations in M along the segments follow variations in petrologic indicators of mantle melt fraction, both showing a preferred length scale of 50 ± 20 km that persists even along much longer ridge segments. In comparison, mean M and axial relief fail to show significant correlations with distance offsetting the segments. These two findings suggest a form of magmatic segmentation that is partially decoupled from the geometry of the plate boundary. We hypothesize this magmatic segmentation arises from cells of buoyantly upwelling mantle that influence tectonic segmentation from the mantle, up.

  20. Neogene exhumation in the eastern Alaska Range and its relationship to splay fault activity in the Denali fault system

    NASA Astrophysics Data System (ADS)

    Waldien, T.; Roeske, S.; Benowitz, J.; Allen, W. K.; Ridgway, K.

    2015-12-01

    Dextral oblique convergence in the Denali fault system results from subduction zone strain in the Alaska syntaxis that is partitioned into the upper plate. This convergence is accommodated by dextral-reverse oblique slip on segments of the main strand of the Denali fault in the center of the Alaska Range and by splay faults north and south of the Denali fault at the margins of the Alaska Range. Low-temp. thermochronometry applied to basement rocks bounded by faults within the Denali fault system aids stratigraphic data to determine the timing and locations of exhumation in the Alaska Range, which augment regional seismicity studies aimed at resolving modern fault activity in the Denali fault system. The McCallum Creek and Broxson Gulch faults are north-dipping faults that splay southward from the Denali fault near the Delta River and mark the southern margin of the eastern Alaska Range. Apatite fission track thermochronometry on rocks north of the McCallum Creek fault shows rapid cooling in the hanging wall coeval with basin development in the footwall initiating at the Miocene-Pliocene boundary. Apatite fission track and apatite (U-Th)/He ages from plutonic rocks in the hanging wall of the Broxson Gulch fault, west of the McCallum Creek fault, show final cooling in the Miocene, slightly younger than hanging wall cooling associated with the Susitna Glacier thrust further to the west. Neogene low-temp. cooling ages in the hanging walls of the Susitna Glacier thrust, Broxson Gulch, and McCallum Creek faults suggest that these structures have been accommodating convergence in the Denali fault system throughout the Neogene. More recent cooling in the hanging wall of the McCallum Creek compared to the Susitna Glacier thrust suggests that this fault-related exhumation has migrated eastward throughout the Neogene. Convergence on these splay faults south of the Denali fault results in internal contraction of the crust south of the Denali fault, implying that the Southern

  1. Discovery of previously unrecognised local faults in London, UK, using detailed 3D geological modelling

    NASA Astrophysics Data System (ADS)

    Aldiss, Don; Haslam, Richard

    2013-04-01

    In parts of London, faulting introduces lateral heterogeneity to the local ground conditions, especially where construction works intercept the Palaeogene Lambeth Group. This brings difficulties to the compilation of a ground model that is fully consistent with the ground investigation data, and so to the design and construction of engineering works. However, because bedrock in the London area is rather uniform at outcrop, and is widely covered by Quaternary deposits, few faults are shown on the geological maps of the area. This paper discusses a successful resolution of this problem at a site in east central London, where tunnels for a new underground railway station are planned. A 3D geological model was used to provide an understanding of the local geological structure, in faulted Lambeth Group strata, that had not been possible by other commonly-used methods. This model includes seven previously unrecognised faults, with downthrows ranging from about 1 m to about 12 m. The model was constructed in the GSI3D geological modelling software using about 145 borehole records, including many legacy records, in an area of 850 m by 500 m. The basis of a GSI3D 3D geological model is a network of 2D cross-sections drawn by a geologist, generally connecting borehole positions (where the borehole records define the level of the geological units that are present), and outcrop and subcrop lines for those units (where shown by a geological map). When the lines tracing the base of each geological unit within the intersecting cross-sections are complete and mutually consistent, the software is used to generate TIN surfaces between those lines, so creating a 3D geological model. Even where a geological model is constructed as if no faults were present, changes in apparent dip between two data points within a single cross-section can indicate that a fault is present in that segment of the cross-section. If displacements of similar size with the same polarity are found in a series

  2. K-Ar age data of clay fault gouges from some major Neoalpine faults

    NASA Astrophysics Data System (ADS)

    Pleuger, J.; Zwingmann, H.; Mancktelow, N.; Manser, M.

    2012-04-01

    In the Central Alps, the Insubric Phase in the sense of Argand (1916, Eclogae geol. Helv. 14, 145-191) was related to underthrusting of South Alpine units below the Penninic nappes along the Periadriatic Fault. Several other large-scale faults were active during the same, though not always the entire, Oligocene to Miocene time span. These faults form an array interpreted as to result from the partitioning of strain induced by the crustal convergence between the European and Adriatic plates (e.g. Handy et al. 2005, Geol. Soc. Spec. Publ. 243, 249-276). With ongoing Alpine convergence and deformation during exhumation there is a general progression from ductile to brittle behaviour on the Periadriatic Fault and kinematically related faults further north (e.g. the Simplon Rhone Fault and a diffuse, discontinous zone of generally dextral strike-slip movement on the southern boundary of the Aar massif). K-Ar dating of fine grained illite from clay fault gouges provides a reliable method for establishing the approximate time of faulting. New results establish that brittle faulting on the northeastern segment of the Canavese Fault (i.e. the part of the Periadriatic Fault SW of Val d'Ossola) occurred around 20 Ma, with south-side-up kinematics. An age of ca. 17 Ma for the crosscutting Giudicarie Fault in the Eastern Alps is effectively identical with an already published pseudotachylyte age and places a lower limit on major and continuous strike slip movements the Periadriatic Fault. The age of brittle faulting further north, on the southern border of the Aar massif, is from 13.6±0.3 to 8.3±1.1 Ma, consistent with the younger cooling and exhumation in this area. The dominantly dextral brittle faulting becoming younger to the north reflects the continued indentation and anticlockwise rotation of Adria as Alpine units become exhumed and progressively welded to the southern block. In contrast to the eastern Alps, there is no field evidence for (westward) lateral extrusion

  3. Characterization of Appalachian faults

    SciTech Connect

    Hatcher, R.D. Jr.; Odom, A.L.; Engelder, T.; Dunn, D.E.; Wise, D.U.; Geiser, P.A.; Schamel, S.; Kish, S.A.

    1988-02-01

    This study presents a classification/characterization of Appalachian faults. Characterization factors include timing of movement relative to folding, metamorphism, and plutonism; tectonic position in the orogen; relations to existing anisotropies in the rock masses; involvement of particular rock units and their ages, as well as the standard Andersonian distinctions. Categories include faults with demonstrable Cenozoic activity, wildflysch-associated thrusts, foreland bedding-plane thrusts, premetamorphic to synmetamorphic thrusts in medium- to high-grade terranes, postmetamorphic thrusts in medium- to high-grade terranes, thrusts rooted in Precambrian basement, reverse faults, strike-slip faults, normal (block) faults, compound faults, structural lineaments, faults associated with local centers of disturbance, and geomorphic (nontectonic) faults.

  4. Gravity constraints on the geometry of the Big Bend of the San Andreas Fault in the southern Carrizo Plains and Pine Mountain egion

    NASA Astrophysics Data System (ADS)

    Altintas, Ali Can

    The goal of this project is to combine gravity measurements with geologic observations to better understand the "Big Bend" of the San Andreas Fault (SAF) and its role in producing hydrocarbon-bearing structures in the southern Central Valley of California. The SAF is the main plate boundary structure between the Pacific and North American plates and accommodates ?35 mm/yr of dextral motion. The SAF can be divided into three main parts: the northern, central and southern segments. The boundary between the central and southern segments is the "Big Bend", which is characterized by an ≈30°, eastward bend. This fault curvature led to the creation of a series of roughly east-west thrust faults and the transverse mountain ranges. Four high-resolution gravity transects were conducted across locations on either side of the bend. A total of 166 new gravity measurements were collected. Previous studies suggest significantly inclined dip angle for the San Andreas Fault in the Big Bend area. Yet, our models indicate that the San Andreas Fault is near vertical in the Big Bend area. Also gravity cross-section models suggest that flower structures occur on either side of the bend. These structures are dominated by sedimentary rocks in the north and igneous rocks in the south. The two northern transects in the Carrizo plains have an ≈-70 mgal Bouguer anomaly. The SAF has a strike of ≈315° near these transects. The northern transects are characterized by multiple fault strands which cut marine and terrestrial Miocene sedimentary rocks as well as Quaternary alluvial valley deposits. These fault strands are characterized by ?6 mgal short wavelength variations in the Bouguer gravity anomaly, which correspond to low density fault gouge and fault splays that juxtapose rocks of varying densities. The southern transects cross part of the SAF with a strike of 285°, have a Bouguer anomaly of ≈-50 mgal and are characterized by a broad 15 mgal high. At this location the rocks on

  5. Fault zone hydrogeology

    NASA Astrophysics Data System (ADS)

    Bense, V. F.; Gleeson, T.; Loveless, S. E.; Bour, O.; Scibek, J.

    2013-12-01

    Deformation along faults in the shallow crust (< 1 km) introduces permeability heterogeneity and anisotropy, which has an important impact on processes such as regional groundwater flow, hydrocarbon migration, and hydrothermal fluid circulation. Fault zones have the capacity to be hydraulic conduits connecting shallow and deep geological environments, but simultaneously the fault cores of many faults often form effective barriers to flow. The direct evaluation of the impact of faults to fluid flow patterns remains a challenge and requires a multidisciplinary research effort of structural geologists and hydrogeologists. However, we find that these disciplines often use different methods with little interaction between them. In this review, we document the current multi-disciplinary understanding of fault zone hydrogeology. We discuss surface- and subsurface observations from diverse rock types from unlithified and lithified clastic sediments through to carbonate, crystalline, and volcanic rocks. For each rock type, we evaluate geological deformation mechanisms, hydrogeologic observations and conceptual models of fault zone hydrogeology. Outcrop observations indicate that fault zones commonly have a permeability structure suggesting they should act as complex conduit-barrier systems in which along-fault flow is encouraged and across-fault flow is impeded. Hydrogeological observations of fault zones reported in the literature show a broad qualitative agreement with outcrop-based conceptual models of fault zone hydrogeology. Nevertheless, the specific impact of a particular fault permeability structure on fault zone hydrogeology can only be assessed when the hydrogeological context of the fault zone is considered and not from outcrop observations alone. To gain a more integrated, comprehensive understanding of fault zone hydrogeology, we foresee numerous synergistic opportunities and challenges for the discipline of structural geology and hydrogeology to co-evolve and

  6. SURVNET: A Fault Tolerant Local Area Network

    NASA Astrophysics Data System (ADS)

    Katz, J. L.; Metcalf, B. D.

    1987-01-01

    In response to the Department of Defense's need to enhance the survivability of command and control systems, The MITRE Corporation developed SURVNET, a survivable fiber optic local area network. The network supports data communications with a fault-tolerant, distributed architecture capable of continued communication despite media failure and node outages. SURVNET is configured as a modified fiber-optic broadcast bus. The physical and data link layers are implemented with a combination of IEEE 802.3 (Ethernet) and an augmented version of IEEE 802.4 token passing bus protocols. Special nodes in the network, incorporating fault-tolerant software, are doubly connected to the fiber bus. Periodically, these nodes broadcast a self-addressed test message to determine if continuity exists on the network segment between the node's two physically separate connections. If a discontinuity is detected, the node utilizes its two connections to bridge between the isolated bus segments.

  7. Fault recovery characteristics of the fault tolerant multi-processor

    NASA Technical Reports Server (NTRS)

    Padilla, Peter A.

    1990-01-01

    The fault handling performance of the fault tolerant multiprocessor (FTMP) was investigated. Fault handling errors detected during fault injection experiments were characterized. In these fault injection experiments, the FTMP disabled a working unit instead of the faulted unit once every 500 faults, on the average. System design weaknesses allow active faults to exercise a part of the fault management software that handles byzantine or lying faults. It is pointed out that these weak areas in the FTMP's design increase the probability that, for any hardware fault, a good LRU (line replaceable unit) is mistakenly disabled by the fault management software. It is concluded that fault injection can help detect and analyze the behavior of a system in the ultra-reliable regime. Although fault injection testing cannot be exhaustive, it has been demonstrated that it provides a unique capability to unmask problems and to characterize the behavior of a fault-tolerant system.

  8. Hayward fault: Large earthquakes versus surface creep

    USGS Publications Warehouse

    Lienkaemper, James J.; Borchardt, Glenn; Borchardt, Glenn; Hirschfeld, Sue E.; Lienkaemper, James J.; McClellan, Patrick H.; Williams, Patrick L.; Wong, Ivan G.

    1992-01-01

    The Hayward fault, thought a likely source of large earthquakes in the next few decades, has generated two large historic earthquakes (about magnitude 7), one in 1836 and another in 1868. We know little about the 1836 event, but the 1868 event had a surface rupture extending 41 km along the southern Hayward fault. Right-lateral surface slip occurred in 1868, but was not well measured. Witness accounts suggest coseismic right slip and afterslip of under a meter. We measured the spatial variation of the historic creep rate along the Hayward fault, deriving rates mainly from surveys of offset cultural features, (curbs, fences, and buildings). Creep occurs along at least 69 km of the fault's 82-km length (13 km is underwater). Creep rate seems nearly constant over many decades with short-term variations. The creep rate mostly ranges from 3.5 to 6.5 mm/yr, varying systemically along strike. The fastest creep is along a 4-km section near the south end. Here creep has been about 9mm/yr since 1921, and possibly since the 1868 event as indicated by offset railroad track rebuilt in 1869. This 9mm/yr slip rate may approach the long-term or deep slip rate related to the strain buildup that produces large earthquakes, a hypothesis supported by geoloic studies (Lienkaemper and Borchardt, 1992). If so, the potential for slip in large earthquakes which originate below the surficial creeping zone, may now be 1/1m along the southern (1868) segment and ≥1.4m along the northern (1836?) segment. Substracting surface creep rates from a long-term slip rate of 9mm/yr gives present potential for surface slip in large earthquakes of up to 0.8m. Our earthquake potential model which accounts for historic creep rate, microseismicity distribution, and geodetic data, suggests that enough strain may now be available for large magnitude earthquakes (magnitude 6.8 in the northern (1836?) segment, 6.7 in the southern (1868) segment, and 7.0 for both). Thus despite surficial creep, the fault may be

  9. Characteristics of Fault Zones in Volcanic Rocks Near Yucca Flat, Nevada Test Site, Nevada

    SciTech Connect

    Donald Sweetkind; Ronald M. Drake II

    2007-11-27

    During 2005 and 2006, the USGS conducted geological studies of fault zones at surface outcrops at the Nevada Test Site. The objectives of these studies were to characterize fault geometry, identify the presence of fault splays, and understand the width and internal architecture of fault zones. Geologic investigations were conducted at surface exposures in upland areas adjacent to Yucca Flat, a basin in the northeastern part of the Nevada Test Site; these data serve as control points for the interpretation of the subsurface data collected at Yucca Flat by other USGS scientists. Fault zones in volcanic rocks near Yucca Flat differ in character and width as a result of differences in the degree of welding and alteration of the protolith, and amount of fault offset. Fault-related damage zones tend to scale with fault offset; damage zones associated with large-offset faults (>100 m) are many tens of meters wide, whereas damage zones associated with smaller-offset faults are generally a only a meter or two wide. Zeolitically-altered tuff develops moderate-sized damage zones whereas vitric nonwelded, bedded and airfall tuff have very minor damage zones, often consisting of the fault zone itself as a deformation band, with minor fault effect to the surrounding rock mass. These differences in fault geometry and fault zone architecture in surface analog sites can serve as a guide toward interpretation of high-resolution subsurface geophysical results from Yucca Flat.

  10. Characteristics of Fault Zones in Volcanic Rocks Near Yucca Flat, Nevada Test Site, Nevada

    USGS Publications Warehouse

    Sweetkind, Donald S.; Drake II, Ronald M.

    2007-01-01

    During 2005 and 2006, the USGS conducted geological studies of fault zones at surface outcrops at the Nevada Test Site. The objectives of these studies were to characterize fault geometry, identify the presence of fault splays, and understand the width and internal architecture of fault zones. Geologic investigations were conducted at surface exposures in upland areas adjacent to Yucca Flat, a basin in the northeastern part of the Nevada Test Site; these data serve as control points for the interpretation of the subsurface data collected at Yucca Flat by other USGS scientists. Fault zones in volcanic rocks near Yucca Flat differ in character and width as a result of differences in the degree of welding and alteration of the protolith, and amount of fault offset. Fault-related damage zones tend to scale with fault offset; damage zones associated with large-offset faults (>100 m) are many tens of meters wide, whereas damage zones associated with smaller-offset faults are generally a only a meter or two wide. Zeolitically-altered tuff develops moderate-sized damage zones whereas vitric nonwelded, bedded and airfall tuff have very minor damage zones, often consisting of the fault zone itself as a deformation band, with minor fault effect to the surrounding rock mass. These differences in fault geometry and fault zone architecture in surface analog sites can serve as a guide toward interpretation of high-resolution subsurface geophysical results from Yucca Flat.

  11. Deformation Monitoring of AN Active Fault

    NASA Astrophysics Data System (ADS)

    Ostapchuk, A.

    2015-12-01

    The discovery of low frequency earthquakes, slow slip events and other deformation phenomena, new for geophysics, change our understanding of how the energy accumulated in the Earth's crust do release. The new geophysical data make one revise the underlying mechanism of geomechanical processes taking place in fault zones. Conditions for generating different slip modes are still unclear. The most vital question is whether a certain slip mode is intrinsic for a fault or may be controlled by external factors. This work presents the results of two and a half year deformation monitoring of a discontinuity in the zone of the Main Sayanskiy Fault. Main Sayanskiy Fault is right-lateral strike-slip fault. Observations were performed in the tunnel of Talaya seismic station (TLY), Irkutsk region, Russia. Measurements were carried out 70 m away from the entrance of the tunnel, the thickness of overlying rock was about 30 m. Inductive sensors of displacement were mounted at the both sides of a discontinuity, which recorded three components of relative fault side displacement with the accuracy of 0.2 mcm. Temperature variation inside the tunnel didn't exceed 0.5oC during the all period of observations. Important information about deformation properties of an active fault was obtained. A pronounced seasonality of deformation characteristics of discontinuity is observed in the investigated segment of rock. A great number of slow slip events with durations from several hours to several weeks were registered. Besides that alterations of fault deformation characteristics before the megathrust earthquake M9.0 Tohoku Oki 11 March 2011 and reaction to the event itself were detected. The work was supported by the Russian Science Foundation (grant no. 14-17-00719).

  12. Multicycle slip distribution along a laboratory fault

    USGS Publications Warehouse

    Chi-Yu, King

    1991-01-01

    Slip distribution along a laboratory fault, which consists of eight spring-connected blocks that are elastically driven to slide on a frictional surface, has been examined for a "long' sequence of slip events to test the applicability of some conceptual models. The distributions of large slip events are found to be quite variable and do not fit the uniform slip or characteristic earthquake models. The rupture initiation points are usually not near the corresponding maximum slip points, in contrast to observations by Thatcher (1990) and by Fukao and Kikuchi (1987) that earthquake hypocenters are commonly near corresponding regions of maximum slip in the fault planes. The results suggest that earthquake prediction monitoring efforts should not be limited to a small region near an asperity but should be spread out to cover the entire fault segment in a seismic gap in order to detect the condition of simultaneous strain buildup. -from Author

  13. An integrated multiscale paleoseismic and neotectonic approach of the Carboneras Fault Zone, SE Spain, and its marine continuation in the Alboran Sea

    NASA Astrophysics Data System (ADS)

    Moreno, X.; Masana, E.; Gracia, E.; Bartolome, R.; Lo Iacono, C.; Rodés, A.; Pallàs, R.

    2009-12-01

    The slow convergence (4-5 mm/yr) between the African and Iberian plates characterises the southeastern Iberian Peninsula and surrounding margins with a wide zone of low to intermediate magnitude seismicity. Shortening is mainly accommodated by a left-lateral strike-slip fault system referred to as Eastern Betics Shear Zone (EBSZ). The NE-SW trending Carboneras Fault Zone (CFZ) with 50 km onshore and more than 100 km offshore is one of the longest structures of the EBSZ. Despite the low seismicity associated to this fault, its morphostructure reveals Quaternary activity, suggesting long recurrence (104 years) behaviour, as found in adjacent structures. Geomorphologic, microtopographic, trenching and dating analyses along the onshore La Serrata section show faulted Quaternary alluvial fans and colluvial wedges related to paleoearthquakes. Trench walls evidence a minimum of 6 events since the Mid Pleistocene. The 3 younger events occurred during the last 41.5 ka, suggesting a mean recurrence period of 13.5 ka. A faulted and buried paleochannel records a minimum of 2 events during the last 30 ka and constrain the last earthquake to AD 772-889. The horizontal maximum displacement observed for the paleochannel is 3 m, suggesting a minimum strike-slip rate of 0.1 mm/a for the last 30 ka, smaller than the 0.6 mm/a strike-slip rate calculated for the last 200 ka by displaced valleys across the NW boundary of La Serrata. This change in the slip-rate can be explained by an underestimation of the paleochannel displacement rate or by a decrease in the strike-slip rate throughout the Quaternary. Detailed bathymetric data from fault segments offshore show differences in the surface expression, and high resolution multi-channel and single-channel seismic profiles reveal the deep structure. From the shelf towards the SW, N45 trace with poor surface expression corresponds to a 2 km wide positive flower structure which smoothly turns into a single and then a couple of parallel traces

  14. Fault Slip Rate of the Kazerun Fault System (KFS), Iran, Investigated Using Finite Element Modeling

    NASA Astrophysics Data System (ADS)

    Shoorcheh, Bijan; Motagh, Mahdi; Baes, Marzieh; Bahroudi, Abbas

    2015-10-01

    A 3D non-homogenous finite element model (FEM) is developed to investigate the spatial variations of interseismic deformation for the Kazerun Fault System (KFS) in the Zagros Mountains of Iran. The model includes 19 fault segments that were extracted from geological maps and previous studies, and the average slips in the dip and strike directions on these segments were computed. The contemporary surface deformation is simulated using a free horizontal detachment surface. The dip angles of the faults in the model are varied at 90°, 70°, 50° and 30° to simulate different 3D representations of the fault systems. Tectonic loading at the boundaries of the region is applied using predicted GPS velocity vectors to the north (southern part of the Central Iran Block) and south (southern region of the Zagros mountain belt), which were obtained by solving inverse and forward problems. Where possible, the fault slip rates that are obtained using our non-homogeneous finite element model are validated using the long-term geologic and instantaneous GPS slip rates. The model is then used to estimate the dip- and strike-slip rates of the fault segments of the KFS for which no a priori information was available. We derive an upper bound of 1 mm/year for the average dip-slip rate in the region, which is consistent with estimates from geomorphologic observations. The modeling results show that in addition to the 4 main faults (Dena, Kazerun, Kareh Bas and Main Recent), other faults, such as the Zagros Front, Main Front, High Zagros and Mishan faults, accommodate up to 2.5 mm/year of the differential movement between the North and Central Zagros. We also investigated the contrast in rigidity between the southern and northern areas of the Zagros mountain belt and found that a rigidity contrast of 2 best explains the GPS data of contemporary surface deformation. Neglecting to account for the rigidity contrast in the model can lead to biased estimates of the fault slip rate of up to

  15. Seismic velocity structure in the Hemet Stepover and Trifurcation Areas of the San Jacinto Fault Zone from double-difference earthquake tomography

    NASA Astrophysics Data System (ADS)

    Allam, A. A.; Ben-Zion, Y.; Vernon, F.; Kurzon, I.

    2013-12-01

    We present tomographic images of crustal velocity structures in the Hemet Stepover and Trifurcation areas of the San Jacinto Fault Zone (SJFZ) based on double-difference inversions of earthquake arrival times. We discretize both regions with a horizontal 250m grid spacing and a vertical 500m spacing within 50km by 50km by 20km volumes. We invert for VP, VS, and hypocenter location using data from 16064 earthquakes recorded at 136 stations. In total, we use 266,969 P and 148,249 S arrivals to constrain the seismic velocity structures in the two regions. With large numbers of both arrivals, we are able to obtain images of VP and VS at similar resolutions, enabling us to make spatial maps of and interpret the VP/VS ratios. Though ray coverage is limited at shallow depths, we obtain high-fidelity images of seismic velocities from 2 to 12 km, and validate the results using checkerboard tests. The tomographic images indicate that the velocity of the trifurcation area as a whole is lower than adjacent unfaulted material. We interpret a 4km-wide low velocity zone in the trifurcation itself as fault zone damage related due to high VP/VS ratio. We also observe clear velocity contrasts across the Buck Ridge, Clark, and Coyote Creek segments of the SJFZ. The Anza segment of the SJFZ, to the NW of the trifurcation area, displays a strong (up to 27%) contrast of VS from 2km to 9km. In the Hemet Stepover, a low velocity zone between the Claremont and Casa Loma Strands narrows with depth, with clear velocity contrasts observed across both segments. A roughly 10km-wide zone of low velocity and low VP/VS ratio at the NW tip of the Hot Springs fault is indicative of either unconsolidated sediments associated with the San Jacinto basin, or fluid-filled cracks within a broad deformation zone. Relocated seismicity tends to align with the surface traces of the various fault strands, though it is offset to the northeast of the Casa Loma-Clark strand and to the southwest of the Hot Springs

  16. Irregular earthquake recurrence patterns and slip variability on a plate-boundary Fault

    NASA Astrophysics Data System (ADS)

    Wechsler, N.; Rockwell, T. K.; Klinger, Y.

    2015-12-01

    The Dead Sea fault in the Levant represents a simple, segmented plate boundary from the Gulf of Aqaba northward to the Sea of Galilee, where it changes its character into a complex plate boundary with multiple sub-parallel faults in northern Israel, Lebanon and Syria. The studied Jordan Gorge (JG) segment is the northernmost part of the simple section, before the fault becomes more complex. Seven fault-crossing buried paleo-channels, offset by the Dead Sea fault, were investigated using paleoseismic and geophysical methods. The mapped offsets capture the long-term rupture history and slip-rate behavior on the JG fault segment for the past 4000 years. The ~20 km long JG segment appears to be more active (in term of number of earthquakes) than its neighboring segments to the south and north. The rate of movement on this segment varies considerably over the studied period: the long-term slip-rate for the entire 4000 years is similar to previously observed rates (~4 mm/yr), yet over shorter time periods the rate varies from 3-8 mm/yr. Paleoseismic data on both timing and displacement indicate a high COV >1 (clustered) with displacement per event varying by nearly an order of magnitude. The rate of earthquake production does not produce a time predictable pattern over a period of 2 kyr. We postulate that the seismic behavior of the JG fault is influenced by stress interactions with its neighboring faults to the north and south. Coulomb stress modelling demonstrates that an earthquake on any neighboring fault will increase the Coulomb stress on the JG fault and thus promote rupture. We conclude that deriving on-fault slip-rates and earthquake recurrence patterns from a single site and/or over a short time period can produce misleading results. The definition of an adequately long time period to resolve slip-rate is a question that needs to be addressed and requires further work.

  17. Thermal Fluid and Fault Interactions at the Intersection of Two Faults, Agua Caliente, California

    NASA Astrophysics Data System (ADS)

    Wood, R. E.; Evans, J. P.

    2011-12-01

    Agua Caliente Springs lies at a unique intersection between the NNW-trending Elsinore fault and the 40° northeast-dipping, likely inactive West Salton detachment fault; it provides an opportunity to study damage zone geometry, fault behavior in crystalline rocks, a left-stepover zone between the Julian and Coyote segments, microseismicity, and the influence of thermal fluids on rock deformation. The Elsinore fault bounds the northwestern flank of the Tierra Blanca Mountains with strike-slip and normal motion; the detachment fault wraps around the northernmost portion of the mountains. Damage along the Elsinore ranges in thickness from a narrow slip plane to > 100 m along the eastern flank of the Tierra Blanca Mountains. Subsidiary faults trend northeast and southeast, and slip orientations vary from normal to strike-slip horizontal motion. Thermal fluids (~30°C) emerge at the intersection of the West Salton detachment and Elsinore faults actively alter the 94 Ma La Posta tonalite pluton, already fractured and crushed during fault slip, to a fine-grained white to orange powder through mineral re-equilibration. Grain sizes decrease with closer proximity to the faults. Fault cores contain thin dark green zones of chlorite ± epidote, and fault surfaces are coated with a thin layer of the same. Origin of the mineralization may be from reworked biotite crystals. We present water chemistry data from the hot springs at Agua Caliente in conjunction with geochemical and petrographic analysis of the surrounding rock. Water analyses include cation and anion measurements, bicarbonate, stable isotopes, tritium, and a multi-month recording of spring conductivity, water level, and temperature fluctuations. Cation geothermometry shows the fluids are enriched in Na, Ca, Mg, K, and Si from broken down quartz, plagioclase, and orthoclase. Water level and temperature data are compared to seismicity during the logging interval; temperatures so far have diurnal fluctuations indicating

  18. Geomorphic mapping of the southern Maacama fault based on LiDAR data

    NASA Astrophysics Data System (ADS)

    Hoeft, J. S.; Sowers, J. M.; Kelsey, H. M.; Prentice, C. S.; Frankel, K. L.

    2008-12-01

    The Maacama fault is an active strike slip fault, and a potentially significant seismic source, within the San Andreas transform system. The fault is located east of and parallel to the San Andreas fault in Sonoma and Mendocino counties, California and is divided into a northern and southern section based on a NW to NNW change in strike. The southern segment comprises 54 km of the fault's 144 km total length and is primarily located in an upland area traversing mountainous terrain. Strain is thought to transfer northward from the East Bay fault zone along the Rodgers Creek fault and, through a right step, to the Maacama fault. LiDAR data collected in a 1-km-wide swath along the southern Maacama fault, as part of the GeoEarthscope project, were used to produce a bare-earth digital elevation model, from which hillshade, topographic contour, slope, and curvature maps with 0.5- to 1-m-resolution were derived. Mapping was primarily conducted digitally in a GIS environment, and interpretation of LiDAR data was supplemented with aerial photograph interpretation and field inspection. Primary, Holocene-age fault-related geomorphic features, consisting of scarps and dextrally offset drainages, define the southern Maacama. These features are sparsely distributed and comprise less than 20% of the fault length. The fault scarps define a sequence of left-stepping, en echelon fault segments with an average segment length of 230 m. By contrast, the northern Maacama fault is better defined geomorphically. The poor expression of the southern Maacama is likely due to the presence of active hillslope processes and low levels of seismicity. Seismicity along the southern segment is lower than that of the northern segment. The Coast Range uplands, primarily composed of Franciscan Complex, is characterized by numerous landslides and experiences annual precipitation of 75 to 180 cm. There is approximately 30 km of overlap between the northern end of the Rodgers Creek fault and the southern

  19. Late Quaternary tectonic activity and paleoseismicity of the Eastern Messinia Fault Zone, SW Peloponessus (Messinia, Greece).

    NASA Astrophysics Data System (ADS)

    Valkaniotis, Sotirios; Betzelou, Konstantina; Zygouri, Vassiliki; Koukouvelas, Ioannis; Ganas, Athanassios

    2015-04-01

    The southwestern part of Peloponnesus, Messinia and Laconia, is an area of significant tectonic activity situated near the Hellenic trench. Most of the deformation in this area is accommodated by the Eastern Messinia Fault Zone, bordering the western part of Taygetos Mt range and the west coast of Mani peninsula. The Eastern Messinia Fault Zone (EMFZ) is a complex system of primarily normal faults dipping westwards with a strike of NNW-SSE to N-S direction attaining a total length of more than 100 km from the northern Messinia plain in the north to the southern part of Mani peninsula in the south. The continuity of the EMFZ is disrupted by overlapping faults and relay ramp structures. The central part of the EMFZ, from the town of Oichalia to the city of Kalamata, was investigated by detailed field mapping of fault structures and post-alpine sediment formations together with re-evaluation of historical and modern seismicity. Several fault segments with lengths of 6 to 10 km were mapped, defined and evaluated according to their state of activity and age. Analysis of fault striation measurements along fault planes of the fault zone shows a present regime of WSW-ENE extension, in accordance with focal mechanisms from modern seismicity. Known faults like the Katsareika and Verga faults near the city of Kalamata are interpreted as older-generation faults that are re-activated (e.g. the 1986 Ms 6.0 Kalamata earthquake on Verga Fault) as part of a system of distributed deformation. New fault segments, some of them previously unmapped like the Asprohoma fault to the west of Kalamata, and offshore faults like Kitries and Kourtissa, are being assigned to the EMFZ. Moreover, a paleoseismological trench was excavated in the northern part of Pidima fault segment, one of the most prominent active segments of the central part of the EMFZ, in order to examine the paleoearthquake record of the fault system. A significant number of historical and instrumental earthquakes in the area

  20. Potential earthquake triggering in a complex fault network: the northern South Island, New Zealand

    NASA Astrophysics Data System (ADS)

    Robinson, Russell

    2004-11-01

    A synthetic seismicity computer model of multiple, interacting faults has been used to investigate potential earthquake triggering in the Alpine-Marlborough-Buller fault network, northern South Island, New Zealand. Of particular interest is whether large, characteristic earthquakes on the central 300-km-long segment of the Alpine fault (average recurrence time of 240 yr) might trigger events to the north and northeast, possible temporal clustering of other large events and stress shadows. The synthetic seismicity model generates long, homogeneous catalogues that sample a wide range of possible stress interactions and stress states allowing statistical analysis. The catalogues used here include ~1500 central Alpine fault events of M >= 7.8 and approximately 2 000 000 other events of magnitudes down to 4.8. These other events occur on four additional segments of the Alpine fault, on 30 segments of the major Marlborough and Buller faults and on 4650 randomly distributed smaller faults. The synthetic seismicity model is of the quasi-static type, governed by the Coulomb failure criterion, with extensions to better account for rupture propagation and fault healing. True rate and state friction and viscoelastic relaxation are not yet included. Mechanical properties are adjusted so that most events rupture an entire fault segment, i.e. the faults behave characteristically. The regional b-value of ~1 thus arises mainly from the fault size distribution. The driving mechanism and fault properties are iteratively adjusted so that the resulting long-term slip rates, single event displacements and recurrence times match the observed, real world values. The major results are as follows. (i) Large Alpine fault earthquakes, M >= 7.8, on the central segment, have recurrence times with a broad distribution, from 81 to 601 yr (average 234 yr). (ii) The regional moment release rate is constant over periods of ~1000 yr, but is quite variable on scales of a few hundred years. (iii) Large

  1. Displacement Addition on Linking Extensional Fault Arrays in the Canyonlands Graben, Utah

    NASA Astrophysics Data System (ADS)

    Commins, D. C.; Gupta, S.; Cartwright, J. A.; Phillips, W. M.

    2003-12-01

    Studies of brittle fault populations over the past decade have revealed that large extensional faults grow by the