The assumption of an eastward dipping fault is based on a suite of test inversions for dip direction and the prevalence of higher relief on the eastern edge of the fault within the study area (Figure 2b). Transform faults are so named because they are linked to other types of plate boundaries. Across this transect, they found that the Chaman fault accommodated ~8.5 mm/yr (±10.3/6.8 mm/yr) of sinistral slip and was likely locked to a depth of 3.4 km. Chaman Fault System is one of the longest (~1000 km) strike-slip faults forming the western boundary of the India plate with Eurasia. Moreover, the cumulative surface displacement maps span a broad range of time intervals (Table 1), meaning they cannot be jointly inverted for creep rate without introducing a rate bias. The example shown is for an inversion that inverts both data sets while keeping fault dip and slip direction fixed. These behaviors in turn act to lengthen earthquake recurrence intervals, limit the maximum magnitude of an earthquake on a particular fault segment, or prevent the occurrence of earthquakes altogether. Similar to the Ornach‐Nal fault, there are few examples of significant earthquakes reliably located on the Chaman fault south of 32°N. The >1000‐km‐long transform fault defining the continental western boundary of the Indian plate (Fig. The Chaman fault is the major strike‐slip structural boundary between the India and Eurasia plates. The relatively fast moving left-lateral, strike-slip Chaman Fault system in southeastern Afghanistan accommodates translational motion between the India and Eurasia plates. An M6.5 earthquake in 1892 near the town of Chaman (29.95°N) is well located on the Chaman fault due to records of offset cultural features (Figure 2) [Griesbach, 1893; Ambraseys and Bilham, 2003]. Frete GRÁTIS em milhares de produtos com o Amazon Prime. At ~30.5°N, near Quetta, Pakistan, the Ghazaband transitions to a more eastward strike and merges with thrust faults of the Sulaiman Hills [Lawrence et al., 1981]. The 95 km long locked segment, herein termed the “Chaman Segment” coincides with the GPS transect of Szeliga et al. I then extracted the cumulative line‐of‐sight displacements within a 40 km × 0.5 km swatch perpendicular to each fault segment. [2012] by exploring the distribution of fault creep rates, variations in geometry and slip direction of the Chaman fault, and changes in locking depth of the Chaman fault as inferred from ascending and descending Envisat and ALOS InSAR time series analysis. The profiles are denoted by variations in locking depth (km). I then individually inspected all interferograms for unwrapping errors, as evidenced by large displacement discontinuities between regions of high coherence. These motions typically result in north-south to northeast-southwest strike-slip motion at the latitude of the 24 September earthquake that is primarily accommodated on the Chaman Fault, with the earthquake potentially occurring on one of the southern-most strands of this fault system. Download Full PDF Package. This earthquake may likewise be misattributed to the Chaman fault or may be mislocated such that it occurred on the Chaman fault south of the Nushki Creeping Segment. The InSAR time series analysis and modeling presented here demonstrates that the southern and central Chaman fault exhibits significant aseismic creep within seismogenic depths shallower than 3 km over a 7.25 year observations period, with the fault commonly locked only to depths of 1 km or shallower (Figures 2, 7, and 9). The Neighbourhood Algorithm also inverted the displacements for long‐wavelength satellite orbital errors (i.e., ramps) that may still be present in the displacement profiles. Please check your email for instructions on resetting your password. This study presents new insights on the Chaman Fault System that connects deformation in the Makran and Himalayan collision zones. As such, my creep rate analysis focuses on the region spanned by Envisat tracks 256 and 406 (Figures 2a and 3a). Processes in Geophysics, Atmospheric Interferograms with substantial signal decorrelation were manually culled. Physics, Solar This inversion strategy does not account for depth variations in slip rate or the slip rate of the Chaman fault at depths greater than 3–4 km, as is discussed further below. The profile designations in both panels are the same as those in Figure, Journal of Advances These experiments do, however, reinforce the value of multiple interferometric look directions for the purposes of exploring unknown fault geometry and slip direction. The variations in creep rate within the Nushki Creeping Segment highlight an import and as yet unresolved gap in our understanding of strain partitioning within this plate boundary zone (Figure 7). 1). Second, inversions that allow both dip and rake angles to vary freely (Figure 8a) exhibit a smaller spread in values than inversions where dip is fixed to 90° (Figure 8b). Further resolving the relative influences of fault coupling and slip partitioning would benefit from additional GPS and InSAR time series observations, as well as estimates of geologic slip rates from multiple locations along these faults in order to better constrain if the short geodetic observation period is representative of long‐term slip rates. Tectonics of Pakistan Pakistan geographically lies between 60°E to78°E & 24°N to 37°N. Additional to ascending track 256, Envisat descending track 406 provides a different viewing geometry that may reduce the nonuniqueness inherent to inverting a single viewing geometry alone (Figures 1b and 3a). Chaman Transverse Fault • Chaman fault is one of the major left-lateral transform faults of Pakistan. Two general patterns are evident: first, inversions that include observations from two look directions prefer shallower rake angles (0–10°) than inversions of a single look direction (8–14°). Szeliga et al. It has high density of active faults and is seismically one of the most active area of the Asia. Locked segments are inferred for portions of the fault where no discrete offset is evident or where locking depth is unconstrained (>3 km depth) by the available observations (Figure 2). Despite these issues, the successful identification of creep and locking with InSAR time series analysis provides a conservative synopsis of fault slip rates in the Chaman fault system. [2012] found slip rates of 8.5 mm/yr and a locking depth of 3.4 km from a GPS transect spanning the Chaman Segment (Figure 2a). The location and strike of the fault plane were also permitted to vary within a reasonable range (±5° strike, 500 m in a fault‐normal direction) to account for local inaccuracies in the mapped fault trace location. and Paleomagnetism, History of Positive displacements indicate motion toward the satellite (LOS shortening), and negative displacements indicate motion away from the satellite (LOS lengthening). Fault dip = 60° to 90° to the east, rake = 20 to −20°. In 1505, a segment of the Chaman Fault system near Kabul, Afghanistan ruptured causing widespread destruction of Kabul and surrounding villages. The Persian Gulf has major economic importance because of oil occurrence in large domes and anticlines of the Arabian platform and Zagros mountain belt, the two geological provinces which border the Persian Gulf (Fig. When combined with an estimated 11 mm/yr slip rate on the Chaman fault, these two faults account for 64–83% of the total plate motion across the plate boundary, leaving 6–13 mm/yr of relative plate motion that is accommodated off of these two structures. As expected given the slight obliquity of the Chaman fault with respect to the plate motion vector of India (Figure 1), inferred rakes exhibit a slightly oblique‐convergent sense. Plate tectonics is the unifying theory of geology. Searching a parameter space, Geodetic determination of relative plate motion in central California, Distribution of aseismic slip rate on the Hayward fault inferred from seismic and geodetic data, The Mechanics of Earthquakes and Faulting, Source dynamics of two great earthquakes of the Indian subcontinent: The Bihar‐Nepal earthquake of January 15, 1934 and the Quetta earthquake of May 30, 1935, Public release of the ISC–GEM global instrumental earthquake catalogue (1900–2009), Fold and thrust partitioning in a contracting fold belt: Insights from the 1931 Mach earthquake in Baluchistan, Interseismic strain accumulation along the western boundary of the Indian subcontinent, Mesozoic ophiolites, sutures, and arge‐scale tectonic movements in Afghanistan, Crustal earthquake instability in relation to the depth variation of frictional slip properties, New empirical relationships among magnitude, rupture length, rupture width, rupture area, and surface displacement, New, improved version of generic mapping tools released, Surface effects of the 16 March 1978 earthquake, Pakistan‐Afghanistan border, Journal of Geophysical Research: Solid Earth. They also found from InSAR observations that the northern Chaman fault (>33°N) likely accommodated velocities of 16.8 ± 2.7 mm/yr. Fault dip = 90°, rake = 0° (left‐lateral strike slip); Fault dip = 90°, rake varies from 20 to −20° (left‐lateral strike slip with a dip‐slip component); Fault dip = 60° to 90° to the east, rake = 0°; and. The inversions presented suggest that there may be some variability in both the dip and slip direction of the Chaman fault along strike, yet these variations are small and indicate that the Chaman fault neither dips substantially nor accommodates significant fault‐normal displacements within the study area, as is expected from plate motion models (Figures 8 and S3) [e.g., Jackson et al., 1995; DeMets et al., 2010; Szeliga et al., 2012]. Second, current observations cannot fully resolve the degree of slip partitioning within the plate boundary zone between India and Eurasia. While I and others are able to identify creeping and locked fault segments along the Chaman fault, the robustness of interpretations drawn from these observations are limited with respect to resolving the distributed fault slip rates of the entire plate boundary zone and the degree of interseismic coupling on the Chaman fault itself. Modern geodetic measurements of fault slip rates within the Chaman transform boundary from GPS are sparse but provide important constraints on relative fault motions. The Chaman fault is an active fault and also locus of many catastrophic earthquakes. In each iteration, the Neighbourhood Algorithm was permitted to find the best fitting combination of model parameters (depth to the top of the fault plane, slip magnitude, and/or dip and rake). Comparison with other major strike-slip faults The Chaman Fault is a major, active geological fault in Pakistan and Afghanistan that runs for over 850 km. Our observations are in very good agreement with this assessment: a 95 km × 3.4 km locked fault accruing a slip deficit of 8.5 mm/yr would produce one M6.6 earthquake every 100 years. Here interferograms that span short time scales (i.e., less than 1 year) are coherent; however, large, short wavelength displacements are apparent, due to drift of the sand dunes, that obscure measurements of stable ground displacements farther than 10–20 km west of the Chaman fault (Figures 2 and 3). Plate Tectonics Theory. Near 29.4°N, inversions that allow rake to vary again find slower creep rates than the fixed rake inversions; however, this discrepancy may be explained by interferometric decorrelation that obscures displacements of >5 km west of the fault. The Chaman fault appears locked south of this section, although it may be difficult to detect creep in this region due to the spatial limitations of the InSAR observations, a deeper locking depth, or slower creep rates (i.e., variable coupling ratio along strike). From this geometry, track 406 should be insensitive to fault‐parallel displacements (displacements perpendicular to the satellite look direction) and provide an important constraint on where the slip direction is purely strike‐slip. This generates potential trade‐offs between inferred coupling of the Chaman fault and partitioned slip rates, both of which can explain the variations in creep rates illustrated in Figure 7. The inferred variations in creep rate may arise from two different sources: variations in the degree of fault coupling on the Chaman fault along strike or partitioning of slip rates onto the neighboring Ghazaband fault and other structures. The rate of creep within creeping segments is heterogeneous along strike, varying in the Nushki Creeping segment from 2 (±1) to 11 (+1/−2) mm/yr (Figure 7). Displacements in the Rigestan Desert have been omitted from the time series analysis because of the rarity with which pixels are coherent, but the limited region of coherence west of the Chaman fault and noise in the time series influence the reliable detection of increasingly deep locking depths. The most notable locked segment in this study area, the Chaman Segment, extends for ~95 km and was the locus of an ~M6.5 event in 1892 [Ambraseys and Bilham, 2003]. Unlike the Ghazaband fault, the Ornach‐Nal fault has produced no known major or destructive earthquakes larger than an Mw5.9 earthquake in 1974 (U.S. Geological Survey (USGS) Comprehensive Catalog [Bilham et al., 2007]). Locking depths greater than 3 km fall within the spread of displacements in model residuals; thus, I denote profiles where the inferred locking depth is greater than 3 km as interseismically locked (Figure 2b). The gray region represents the spread of residual displacements from a suite of slip rate inversions that is used as a proxy for a deformation detection threshold. By extension, slip rates inferred from profiles with locking depths >3 km should be considered unconstrained. Learn more. Summary. From the south, the Chaman fault starts at the triple junction where the Arabian Plate, the Eurasian Plate and the Indo-Australian Plate meet, which is just off the Makran Coast of Pakistan. The Chaman Fault is a major, active geological fault in Pakistan and Afghanistan that runs for over 850 km. I approximated an infinitely long strike‐slip fault by fixing the downdip width and along‐strike length of the fault plane to 100 km. I find that the fault deviates little from a vertical geometry and accommodates little to no fault‐normal displacements. Tectonically it is located in the region of intersection of three plates, Indian, Eurasian and Arabian sea plate. and Petrology, Exploration Chaman Fault Last updated March 19, 2019.