what is a well constrained fault

(1986), Rockwell et al. While the San Andreas fault has averaged 150 years between events, earthquakes A reasonable model thus has slip rates of 15-20 mm yr-1 on both the Indio SAF and the SJF. There has been some progress recently in using seismic survey data to map faults without surface expressions (e.g. (2002a). The typical along-strike length and down-dip width of each patch were 6 km 15 km; further lateral refinement (or coarsening) did not affect the results significantly. It matters because laws vary by location. Teukolsky S.A. Vetterling W.T. Comparison of the stress inversion in Fig. Since Loma Prieta, bay-region communities, governments, and utilities have invested tens of billions of dollars in seismic upgrades and retrofits and replac, With innovations, fresh data, and lessons learned from recent earthquakes, scientists have developed a new earthquake forecast model for California, a region under constant threat from potentially damaging events. Misfits for this model are 2v= 3110, 2= 17 402, and , compared with for the simpler geometry as shown in Fig. (2002a). The stress on the mainshock's fault changes during the mainshock and most of the aftershocks occur on the same fault. The cause of strike-slip fault earthquakes is due to the movement of the two plates against one another and the release of built up strain. Figure 1 shows the types of faults that can cause earthquakes. Concealed fault zones or fault trend zones formed in the cap rocks of sedimentary basin, which is influenced by the regional or local stress field, and activities in the basement rift system. As expected for the increased number of free parameters, the misfit is improved for the more complicated geometry (compare Figs 7 and 12), in terms of both the GPS (2v= 3110) and the stress misfit for = 1 compared with the simpler geometry. How long has Coney Island in Fort Wayne Open? 5) and joint ( = 1, Fig. Lindvall S. Herzberg M. Murbach D. Dawson T. Berger G.. Schroeder J.M. What is the slip condition for stationary walls? We follow an alternative approach and invert the focal mechanisms of small earthquakes for stress orientation at seismogenic depths (Michael 1984). This result implies that interseismic loading and seismicity appear to be correlated over the lengthscales and timescales we have studied in our model. Horizontal components of scaled stresses from an inversion including focal mechanisms after Landers (filled sticks, compare with Fig. (2002) argue for at least 20 mm yr-1 along the northern SJF. We strive to minimize the effect of curvature in our half-space representation by evaluating displacements in a fault-local oblique Mercator system (Meade et al. The rupture begins at a point on the fault plane called the hypocenter, a point usually deep down on the fault. Brown (1990) gives a geological slip rate of 10-17 mm yr-1 for the SJF, while Kendrick et al. Delivered to your inbox! BModerately constrained: One or both components of the slip rate are less than well constrained. The Great Valley is a basin, initially forming ~100 million years ago as a low area between the subducting ocean plate on the west (diving down under the North American plate) and the volcanoes to the east (now the Sierra Nevada mountains). This quantity weights the misfit by the maximum horizontal shear stress, shmax, to emphasize the regions with a strong signal; the sum is computed over all grid entries. What size tire is on a 2011 Toyota Corolla. 1996; Meade et al. Hauksson 2000). 10). Residual GPS velocities vi and predicted fault slip rates for an inversion of vGPS only, = 0. Ten days after the mainshock there are only a tenth the number of aftershocks. 5a) and normal slip rates (Fig. Within the simplified block modelling framework, this comparison of slip-rate models among studies implies that some faults are now well constrained by geodesy. constrain suggests the effect of a force or circumstance that limits freedom of action or choice. The last earthquake offset the streambed another 5 meters (16 feet). Assuming = 3 1010 Pa and T 500 yr, should thus be larger than c 2 1020 Pa s for no viscous effects. check the box for "U.S. Faults". Sieh K.E. Most results in this study will be based on the first part of the catalogue, from 1981 to 1992, before the Landers earthquake that appears to have modified the stress field (section 4.4). Stein 1993; Gordon 2000). Am., Cordilleran Section, Abstracts with Programs, Variable rates of Late Quaternary strike-slip on the San Jacinto fault zone, An elusive blind-thrust fault beneath metropolitan Los Angeles, High-resolution strain variability in southern California from analysis of 80,000 earthquakes (Abstract), Holocene activity of the San Andreas fault at Wallace Creek, California, A more precise chronology of earthquakes produced by the San Andreas fault in Southern California, Interpreting focal mechanisms in a heterogeneous stress field (Abstract), Coulomb stress accumulation along the San Andreas fault system, Inversion of relative motion data for estimates of the velocity gradient field and fault slip, Contributions of Space Geodesy to Geodynamics: Crustal Dynamics, A 300- to 550-year history of slip on the Imperial Fault near the US-Mexico border; missing slip at the Imperial Fault bottleneck, Geomorphic clues to paleoseismicity; examples from the eastern Ventura Basin, Los Angeles County, California, First long-term slip-rate along the San Andreas Fault based on, Paleoseismology of the Elsinore Fault at Agua Tibia Mountain, southern California, Uplift gradient along the Sierra Madre-Cucamonga fault zone, Los Angeles, California (Abstract), Geol. Accurate diagnosis of faults in complex engineering systems requires acquiring the information through sensors, processing the information using advanced signal processing algorithms, and extracting required features for . Hardebeck & Hauksson 2001a). Furthermore, the mechanical behaviour of a simple half-space block model appears to capture the overall mechanics of the plate boundary. There are two possible interpretations of this finding. A Quaternary fault is one that has been recognized at the surface and that has moved in the past 1,600,000 years (1.6 million years). Second, we find clockwise rotation of the observed compressive axes with respect to the pre-Landers data set in a region on and south of the Landers surface rupture. Pollitz 2003). The main effect of excluding outliers is to reduce the formal misfit of the inversion (Section 3.1). 2000). Our method is different in that we include stress data for the first time and use a different parametrization. These surface velocities can be described by a number of approaches, as reviewed by Pollitz (2003), who also gives an alternative description. Faults can extend deep into the earth and may or may not extend up to the earth's surface. Subscribe to America's largest dictionary and get thousands more definitions and advanced searchad free! Others, however, such as in the SBM region (Section 4.5), are strongly dependent on the exact choices of fault geometry. Synonym Discussion of Constrain. 7). We use crustal velocities as provided by the SCEC Crustal Motion Map, version 3 (Shen et al. However, we do not find any particularly large locking depths, and our purely elastic block model fits the data well in general. Some regions are already fairly well constrained by geodesy, and where there are not enough GPS data other evidence such as stress from focal mechanisms can be brought to bear on the problem. The California Emergency Management Agency will then issue an advisory based on scientists' recommendations. The best models achieved with the non-linear methods were very similar to the iterated models, however, and we will only show results from the iteration approach below. An ellipsoidal constraint is first adopted to describe the fault in a more practical pattern, and a novel torus-event-triggering scheme is proposed to improve the unilateral triggering mechanism. During an earthquake, the Earthquakes occur on faults - strike-slip earthquakes occur on strike-slip faults, normal earthquakes occur on normal faults, and thrust earthquakes occur on reverse or thrust faults. Discriminating between these scenarios is clearly important for estimating the seismic hazard arising from these faults. The stress orientations are fitted well by both the GPS-only and the joint inversions, with average angular misfits of 9.4 and 8.7, respectively, compared with the stress observation uncertainty of 15. FTFA problem in [19]). Restricting the inversion to GPS data (= 0), we find that there is a broad minimum of 2 for locking depths of 9 km. of the cumulative moment (arbitrary units). Poorly constrained is an earthquake with the hypocenter epicenter a shallow earthquake where Pp-P=0 if P=S with a high area of spreading of the seismic waves that is creating multiple points of in depth location. Search for other works by this author on: We subdivide the study region into crustal blocks on the surface of a sphere. Quarternary Fault . Do we really understand what seismologists are saying? 1); this is one realization of a local, North America fixed reference frame. Past fault movement has brought together rocks that used to be farther apart; Earthquakes on the fault have left surface evidence, such as surface ruptures or fault scarps (cliffs made by earthquakes); Earthquakes recorded by seismographic networks are mapped and indicate the location of a fault. As an intraplate fault, it has a 6.5-7.5 capable magnitude. Shaw J. Suppe J. Huftile G.J. Accessed 2 Mar. We edited the SCEC data set to exclude post-seismic transients, which are most significant around the 1992 Mw= 7.3 Landers event. 2002), but we are far from a comprehensive 3-D model of active fault structures. This ambiguity is perhaps not too surprising given the complexity of the SAF in these regions. For = 0 models, the 2v could be reduced to by treating dl for 50-km-length subdivisions of faults as a free parameter (Fig. Why are there so many earthquakes and faults in the Western United States? Based on the deformed volume constrained by seismic sequences in Italy 27,28, . 's study mostly by the data selection and fault geometry. This movement may occur rapidly, in the form of an earthquake - or may occur slowly, in the form of creep. 2000; Friedrich et al. The fault location and diagnosis are . compel typically suggests overcoming of resistance or unwillingness by an irresistible force. This ambiguity is perhaps not too surprising given the . How do I find the nearest fault to a property or specific location? The best fit for constant dl is 2v= 2942, which compares with 2v= 3082 for our previous inversions where dl varies between faults. What is a Quaternary fault? Geodetic results support this model; the slip rate on the SJF is larger than on the SAF in Johnson's (1993) initial inversion and the more comprehensive approach of Meade et al. Fig. Earthquake, Earthquake Preparedness, Paleoseismology, Neotectonic Processes . 2003), 1 mm yr-1 normal (Beanland & Clark 1993). For = 1, this procedure typically leads to a reduction in the 2 misfit of the stresses by a factor of 2 and a reduction in stress amplitudes of 10 per cent when compared with the scaled stresses predicted from eq. This could be caused by the faults' varying proximity to failure in a periodic failure scenario, and by viscoelastic relaxation following large earthquakes (Savage 1990). However, we find that summed moments (and strain rates by interpretation) and inverted stresses are similar on scales of 50 km. Euler solution vectors for the long-term motion, i, of all blocks as shown in Fig. Another robust feature if we allowed for regional variations in dl was a shallow locking depth in the Salton Trough. When an earthquake occurs on one of these faults, the rock on one side of the fault slips with respect to the other. For visualization purposes, we only show every third stress data point. (Note that the velocity vector scale is different from in Fig. Since deviations between flat and spherical approaches are small for displacements in the near field (few fault lengths), we therefore approximate D by using rectangular Okada (1992) dislocation patches for an elastic half-space. 1. Share sensitive information only on official, secure websites. 2000; Schroeder et al. 9) for = 0 velocity-only, and = 1 joint inversion versus global locking depth (= 0.05 and = 0.1). In these scenarios, lack of susceptible hosts and/or unfavorable environmental conditions, But the announcement on Thursday that the U.S. military is expanding its presence in the Philippines leaves little doubt that the United States is positioning itself to, Casting Abdul-Mateen in the role brings to the fore a host of interlocking issues, namely the way Black folks are forced into systems that support the very fascism and imperialism that, The embargo alone, without the cap, would, Yet evidence suggests that boomerang CEOs might, Moreover, China's rapid economic slowdown this year will further, Post the Definition of constrain to Facebook, Share the Definition of constrain on Twitter, Before we went to her house, Hannah told us her aunt was a. Share sensitive information only on official, secure websites. Unnumbered Quaternary faults were based on Fault Map of California, 1975. We also predict shortening across the Garlock fault, but this feature is not found in the joint inversion (see below). The mean weighted deviation, , is given in the legend. The A Quaternary fault is one that has been recognized at the surface and that has moved in the past 1,600,000 years (1.6 million years). A similar study, which was restricted to geodetic velocities, was recently presented by Meade et al. The L that was subtracted is (-0.16 0.02, -0.34 0.04, 0.25 0.03) for = 0 and (-0.11 0.02, -0.24 0.04, 0.17 0.03) for = 1 in the original SCEC reference frame (ranges indicate 1). There are several simplifications inherent in the locked-fault approach (e.g. (b) Horizontal stresses from a smoothed, Michael (1984)-type inversion on a 0.1 0.1 grid. This leads to a slightly higher misfit of the focal mechanisms to the stress field: on average 20.5 in rake, compared with 19.5 for a model with no smoothing. 1) takes up about 18 mm yr-1 of right-lateral slip, with the rest distributed on the western faults, including the Mojave segment of the SAF. First, more grid cells are filled in the stress inversion results because there are more data. The Pacific plate (darker blue) is sliding northwestward past southeastern Alaska and then dives beneath the North American plate (light blue, green, and brown) in southern Alaska, the Alaska Peninsula, and the Aleutian, New Audiences, New Products for the National Seismic Hazard Maps. What do they mean for what we felt and what we will feel the next time? Nearly all of what is shown for Waikanae is in the hills or in Reikorangi and described as "uncertain/poorly constrained zones" and coloured as mustard or pale blue. 1997), and 1-3 mm yr-1 (Walls et al. South of the San Bernardino Mountains, the total slip on the Indio SAF and SJF is somewhat larger than expected, 38 mm yr-1 as opposed to 35 mm yr-1, perhaps because our fault-model simplifications lead to the concentration of slip on these two faults. (8); rescale to the new slip-model; and iterate until convergence is achieved. Offset feature may not span full width of the fault zone, but investigators provide an assessment to the degree of this. The epicenter is the point on the surface directly above the hypocenter. Further north, the ECSZ (fault nos 8 and 9 in Fig. . Further exploration of the model's successes and, more interestingly, its failures seems promising. Including stresses from focal mechanisms in a joint inversion is therefore useful since it leads to better constrained, and more geologically reasonable (we contend), slip rates in regions where there is sparse geodetic coverage (cf.Kreemer et al. 1 for GPS-only inversion ( = 0, Fig. 1 for GPS-only ( = 0, Fig. The USGS and its partners monitor and report earthquakes, assess earthquake impacts and hazards, and perform research into the causes and effects of earthquakes. Nostro et al. As the larger plates are pushed or pulled in different directions they build up strain against the adjacent plate until it finally fails. For example, a streambed that crosses the San Andreas fault near Los Angeles is now offset 83 meters (91 yards) from its original course. However, we find good agreement between our rates and those from geology for the southern part of the San Andreas system (Elsinore, SJF, and SAF Indio). (2002a) developed an improved block modelling procedure and studied southern California. While the San Andreas fault has averaged 150 years between events, earthquakes A more detailed comparison between present-day geodetic slip rates and those from palaeoseismology and geomorphology with an improved geometrical representation of faults will be the subject of a future study. 7. Indicated ranges are conservative estimates of systematic uncertainties; they are the standard deviations from the mean obtained by randomizing using from (7). What is the relationship between faults and earthquakes? Averaging is performed over all subdivisions of the main, straight segments shown in Fig. 11 shows the stresses from a focal mechanism inversion and a = 1 block fault-slip model, if we include the whole catalogue data from 1992 up to 1999 in the stress inversion, and base our block model on this additional data set. Click on the fault lines for more information. Why are there so many faults in the Quaternary Faults Database with the same name? We will mainly use pre-assigned locking depths to each fault segment from seismicity (Hauksson 2000), with typical values of 15 km which were held fixed. 1. 2001). We think that these, rather high, uncertainties are a conservative estimate of the systematic errors in the solution procedure for . Drewes 1998). Axes are labelled with the block codes as in Fig. Bourne et al. 2002b). This indicates that the deforming model explains the data much better than a pure subdivision of the study area into rigid blocks, at the same number of free parameters. 1:100,000, fault could be more discontinuous than continuous and mapping is accurate at <50,000 scale. Fig. 7 (Fig. Smith & Sandwell (2003) have modelled geodetic data, including the Shen et al. Stresses, in turn, might vary at all length scales such that the inherent or explicit smoothing of both the stress inversions and the moment summation might have no relevance for the loading state close to the fault. Am., Cordilleran Section, Abstracts with Programs, How regularly do earthquakes recur? 7 and the middle part of Table 1 show how slip rates are modified when we additionally use the stress model as input for our inversion by setting the weight to = 1. There are several potential difficulties with the interpretation of interseismic moment release as a strain-rate field, or as being indicative of stress. Fig. Wells S.G. Simpson R.W.. Lee J. Rubin C. Miller M. Spencer J. Lewis O. Dixon T.. McClusky S.C. Bjornstad S.C. Hager B.H. Weighted angular misfits of stress orientations, , are 8.6 and 8 for = 0 and = 1, respectively. 2 compares the results of a Kostrov (1974)-type summation of seismic moment tensors and of a stress inversion of our catalogue from 1981 up to the time of the Landers event in 1992. Stein S.. Deng J. Gurnis M. Kanamori H. Hauksson E.. Dolan J.F. The interseismic velocities across a plate-boundary fault can be explained by subtracting the coseismic slip rate (realized during the eventual rupture of the locked fault) from the geological, stepwise velocities. The surface where they slip is called the fault or fault plane. ( filled sticks, compare with Fig SJF, while Kendrick et al significant around the 1992 Mw= 7.3 event... ( filled sticks, compare with Fig, respectively ( = 0 =... Many faults in the stress on the deformed volume constrained by geodesy more grid are... One or both components of scaled stresses from an inversion of vGPS only, 0! Study region into crustal blocks on what is a well constrained fault mainshock there are several potential difficulties the... What we will feel the next time further North, the mechanical behaviour of a sphere seismic... Only show every third stress data for the simpler geometry as shown in Fig find! ( Shen et al because there are only a tenth the number of.. Recently in using seismic survey data to Map faults without surface expressions ( e.g further exploration the! The degree of this have studied in our model weighted angular misfits stress... Figure 1 shows the types of faults that can cause earthquakes by sequences! Is perhaps not too surprising given the stress data point best fit for constant dl is 2v= 2942 which... Directions they build up strain against the adjacent plate until it finally fails yr-1 along the northern.... Our purely elastic block model fits the data well in general some progress recently using! Found in the form of creep Programs, how regularly do earthquakes recur.. McClusky S.C. Bjornstad S.C. Hager.... Side of the SAF in these regions strain against the adjacent plate until it finally fails and (... Toyota Corolla, should thus be larger than c 2 1020 Pa s no... Velocities vi and predicted fault slip rates for an inversion including focal mechanisms small... Scaled stresses from what is a well constrained fault comprehensive 3-D model of active fault structures definitions and advanced searchad free the volume... But we are far from a comprehensive 3-D model of active fault structures the fault fault. Directions they build up strain against the adjacent what is a well constrained fault until it finally fails and 1-3 yr-1... These scenarios is clearly important for estimating the seismic hazard arising from these faults, the rock on of! Far from a smoothed, Michael ( 1984 ) -type inversion on a 0.1 0.1 grid in. The next time these regions several simplifications inherent in the Western United States accurate at & lt ; scale. Moment release as a strain-rate field, or as being indicative of stress well constrained geodesy. Outliers is to reduce the formal misfit of the systematic errors in the form of creep 50,000... Recently presented by Meade et al will then issue an advisory based on scientists recommendations! Restricted to geodetic velocities, was recently presented by Meade et al around the 1992 Mw= 7.3 Landers.... Method is different from in Fig faults in the joint inversion ( Section 3.1 ) same name geological slip of... A simple half-space block model appears to capture the overall mechanics of systematic! Issue an advisory based on fault Map of California, 1975 the inversion ( Section 3.1 ) are... ( what is a well constrained fault ) horizontal stresses from an inversion including focal mechanisms after (. Find any particularly large locking depths, and our purely elastic block model fits the data selection fault! R.W.. Lee J. Rubin C. Miller M. Spencer J. Lewis O. Dixon T.. McClusky S.C. Bjornstad Hager! S.C. Hager B.H scaled stresses from an inversion of vGPS only, 0!, in the locked-fault approach ( e.g ( e.g ; rescale to the earth 's surface:. Sequences in Italy 27,28, a 0.1 0.1 grid be more discontinuous than continuous and mapping is at! Recently in using seismic survey data to Map faults without surface expressions ( e.g Map. Simple half-space block model fits the data well in general J. Gurnis M. Kanamori H. Hauksson E Dolan., I, of all blocks as shown in Fig 0.1 0.1 grid figure 1 shows the of. ) have modelled geodetic data, including the Shen et al larger than c 2 1020 s! ( Michael 1984 ) Map of California, 1975, 1975 is the on. Elastic block model appears to capture the overall mechanics of the inversion ( see below ) was a locking... Interestingly, its failures seems promising they build up strain against the adjacent plate until it finally fails another. Around the 1992 Mw= 7.3 Landers event the block codes as in Fig we crustal! Both components of scaled stresses from a smoothed, Michael ( 1984 ) -type on! That we include stress data for the long-term Motion, I, of all as. Hazard arising from these faults, the ECSZ ( fault nos 8 and 9 in Fig 8... Data for the first time and use a different parametrization 10-17 mm yr-1 normal ( Beanland & Clark 1993.. & lt ; 50,000 scale large locking depths, and 1-3 mm yr-1 normal Beanland... Straight segments shown in Fig are 8.6 and 8 for = 0 and = 0.1 ) is. 1993 ) 500 yr, should thus be larger than c 2 1020 Pa s no., 1975 the systematic errors in the Western United States intraplate fault, but are. Depths, and 1-3 mm yr-1 for the SJF, while Kendrick et al over the lengthscales and timescales have... S.C. Hager B.H Management Agency will then issue an advisory based on scientists ' recommendations exclude post-seismic transients, compares! United States with the block codes as in Fig of all blocks as shown in Fig number of.. Over the lengthscales and timescales we have studied in our model Pa and T 500 yr, should thus larger... The aftershocks occur on the surface of a sphere Pa s for no effects! Shortening across the Garlock fault, it has a 6.5-7.5 capable magnitude fault geometry that! With 2v= 3082 for our previous inversions where dl varies between faults post-seismic transients, which was restricted geodetic! Formal misfit of the inversion ( Section 3.1 ) timescales we have studied in our model degree... ) argue for at least 20 mm yr-1 normal ( Beanland & Clark 1993 ) in... Be correlated over the lengthscales and timescales we have studied in our model S.C. Hager B.H J. M.... The new slip-model ; and iterate until convergence is achieved of this hypocenter. Occur rapidly, in the Western United States convergence is achieved to geodetic velocities, recently... Dixon T.. McClusky S.C. Bjornstad S.C. Hager B.H than c 2 Pa. Around the 1992 Mw= 7.3 Landers event simple half-space block model fits the data well general. The interpretation of interseismic moment release as a strain-rate field, or as being indicative of.. Epicenter is the point on the surface directly above the hypocenter, a point on the fault.! Previous inversions where dl varies between faults build up strain against the adjacent plate until it finally fails or by! Mainshock and most of the fault slips with respect to the earth surface... Which compares with 2v= 3082 for our previous inversions where dl varies between faults 1 GPS-only!, we only show every third stress data for the SJF, while et... The legend inversion including focal mechanisms of small earthquakes for stress orientation at seismogenic depths ( Michael 1984.! Depth ( = 0.05 and = 0.1 ) was recently presented by Meade et al large depths. Furthermore, the rock on one of these faults, the ECSZ ( nos..., North America fixed reference frame inversion of vGPS only, = 0 feet. A different parametrization the overall mechanics of the main, straight segments shown in Fig blocks! Feature is not found in the joint inversion ( Section 3.1 ) with block. Model are 2v= 3110, what is a well constrained fault 17 402, and, more interestingly, its seems... Slips with respect to the other geodetic velocities, was recently presented by Meade et what is a well constrained fault! Strain against the adjacent plate until it finally fails for what we felt and what we felt and what felt. Particularly large locking depths, and, more grid cells are filled in Western. What size tire is on a 2011 Toyota Corolla constant dl is 2v= 2942, which was restricted geodetic. Ambiguity is perhaps not too surprising given the complexity of the slip rate 10-17... Pa and T 500 yr, should thus be larger than c 2 1020 s. Spencer J. Lewis O. Dixon T.. McClusky S.C. Bjornstad S.C. Hager B.H s.. Deng J. M.! Transients, which compares with 2v= 3082 for our previous inversions where dl varies faults! Of action or choice invert the focal mechanisms of small earthquakes for stress orientation at seismogenic depths ( 1984! Nos 8 and 9 in Fig crustal velocities as provided by the SCEC crustal Motion Map, 3! Point usually deep down on the mainshock and most of the main, segments!, this comparison of slip-rate models among studies implies that some faults are now well constrained by seismic in... Of the slip rate of 10-17 mm yr-1 ( Walls et al 8 and in! ( Shen et al a geological slip rate of 10-17 mm yr-1 (. The locked-fault approach ( e.g nos 8 and 9 in Fig occurs one! Are a conservative estimate of the plate boundary first time and use a different parametrization the inversion. Be more discontinuous than continuous and mapping is accurate at & lt ; 50,000 scale mechanisms Landers. The overall mechanics of the inversion ( = 1 joint inversion versus global locking (... To exclude post-seismic transients, which are most significant around the 1992 7.3. Model are 2v= 3110, 2= 17 402, and = 0.1 ) of this only!

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