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I I Nnhval restomtion from tfie effects of the 1064 es*thqueke at Portege, maern Alaske During the 1964 AIaska earthquake, the land in the Portage area (loc. 11, fig. 44) subsided about 2 m owing to local and regional subsidence (Kachadoarian, 1968; YcCuUoch and BonWa, 1870). An area of about 18 km was lowered into the intertidal zone of the Turnagain Arm (Ovens)~ine and others, 19761, and the encroaching tidal waters killed forest, shrub, and grassland communities that the Portege area sup ported. These tidal waters also caused rapw sp- rnentation in the area, and by 1974 about 20x10 m of silt had accumulated in a layer averaging 1.5 m in thickness (Ovenshine and others, 1978). Geologk? data available on the pre-1964 earthquake sediment in the Portage area suggest that the cycle of subsidence and restoration had occurred at least twice previously during Holocene time (Oven- shine and others, 1976). To determine the rate of sedimentation and the time required for restoration at Portage due entirely to sedimentation, Ovenshine and Kachadoorian (1976, fig. 18) developed a mode1 based on data frorn the cycle initiated by the 1964 earthquake. The data available to develop thk model for estimating the rate of sedimentation were that: (1) The total subsidence was about 2 m, and (2) the aver- age thickness of sediment accumulated during the 10- yew period 1964-74 was 1.55 m. The sedimentation model (fig. 71) derived by Ovenshine and Kachadoorian predicts the total thickness of sediment acclirnulated at any given time after the 1964 earthquake. The curve is based on the equation where is the total thickness of sediment accumulated at time & S is the total subsidence due to the 1964 earthquake, g=0.1492, and 1 is the time (in years) slnce 1964. The value of the constant k was deter- mined for E=2 m, A=1.55 m, and 1=10 years. (In Ovenshine and Kaohadoorianrs report, the minus sip was inadvertently omitted in the value given for the constant &) The curve generated by the model (3, fig. 71; Ovenshine and Kachadoorian, L976, fig. 18) predicts that sedimentation in the Portage area will cease by the year 2011 and will be approximately Qa-percent complete by 1989. Results of recent investigations by Bartsch- WLnkler and Garrow (1982) and ourselves indicate that sedimentation in the Portage area hed stopped by summer 1961. Bartsch-Winkler and Garrow have con- cluded Chat the Portage wea was in the flnal recon- struction phase of the sedimentation cycle in summer 1980. We observed the presence of lush vegetation and the occurrence of Succinea sp. (a freshwater gastro- pod) on the higher mudflats during summer 1981. These observations indicate that sedirnentatlon had StoppeU in Portage by 1981, or about 23 years sooner than predicted by Ovenshine and Kachadoorian (1976). Curve 3 (fig. 711, derived from Ovenshine and Kachadoorianfs sedimentat ion model, indicates that by 1980 about 1.80 m of sedimentation would have occurred in the Portage area, or about 20 cm less than the 2.0 m of subsidence to which the area was subjected. Actually, only 1.75 m of aedimentatlon had occurred by 1980. Apparently, either the model is incorrect, or some physical factor is responsible for this discrepancy. The discrepancy is due to postearthquake tectonic rebound, as reported by Brown and others (1977). No rebound was measured at Portage between 1964 and 1968, and about 20 am of rebound occurred between 1968 and 1975 (curve 5, fig. 71; Brown and others, 1977, fig. 2). We have, however, extrapolated the curve from the years 1975-82 on the basis of an analysis of Brown and others' data. Curve 1 (fig. 711, which reprssents the ground-surface elevation relative to the post-1964 surface elevation, is based on the addition of curve 3 (predicted amount of sedimentation frorn equation 1) and curve 5 (amount of tectonlc uplift after 1964). This curve, whlch intersects the 2.0-rn (amount of subsidence at Port~ge) line at mid-1978, indicates that sedimentation should have stopped at that time. Field data indicated that some sedimentation was occurring during summer 1978, albelt slight. Pigure 71.-Rate of sedimentation, amount of uplift, and sedlment+wface elevation relative to past-1964 earthquake elevation. Curve 1, sediment-surface elevatlon based on addition of curves 3 and 5; curve 2, actual sediment-surface elevation based on addition of curves 4 and 5; curve 3, predicte amount of sedimentation from equation pg1-e-1; curve 4, actual amount of sedimentation; curve 5, tectonic upUft in Portage area. Ovenshine and KachadoorIanrs (1976) model sedimentation-ate aurve was based on an assumption of no tectonic uplift and thus does not consider the effect of tectonio uplift on the sedimentation rate. Any uplift of the Portage area would naturally slow down the sedimentation to a rate below that predicted by the model. The equation on which the predictive tt
curve is based indicates that 6.1 cm of sedimentation SOUTHEASTERN ALASKA should have occurred in the 1-year period between 1974 and 1975; however, we measured only 5 cm of (Figure 72 shows study areas discussed) sedimentation for this period. Although 0vGshine and Kachadoorian did not consider this difference to be significant, we now believe that the difference of 1.1 cm of sedimentation is due to tectonic uplift. An analysis of the predictive-model sedimentation-rate By J- R saleebyl, George E Gekekl, G. Zknald curve and the uplift curve, extended to 1982, indicates 3berlein, that by 1980 the amount of actual and Henry C. Berg ,sedimentation at Portage was 5 om less than predicted: The actual sedimentation curve (4, fig. 71) indicates that 1.75 m Geologic mapping and zircon leadlurenium gmof sedimentation occurred by 1980 instead of the 1.80 chronologic studies on southern Prince of Wales Island rn predicted. Curve 2 (fig. 71), which represents the and southern Annette bland (area 10, fig. 72; fig. 73) actual ground-surface elevation relative to the post- have delineated a regional rnetaigneous complex that 1964 earthquake ground elevation, is based on the addition of the tectonic-uplift curve (5) and the actualsedimentation curve (4). Curve 2, which intersects the 2.0-m line in the year 1980, indicates that sedimentation stopped in the Portfge area in 1980, as suggested by field data. The slope of curve 2 becomes the same as that of the uplift curve after deposition stopped in 1980. on the basis af the data available, We believe tnat the model proposed by Ovenshine and KachadoorIan (1976) was a valid approach to estimate the time required for natural restoration due only to sedimentation from the effects of the 1964 earthquake at Portage, Alaska. REFERENCES CITED Bartsch-Winkler, S. R, and Garrow, H. C., 1982, Depositional system approaching maturity at Portage Flats, & Cmnrad, W. L., ed., TRe Ulrited States Geological Survey in Alaska: Accom- plishments during 1980: U.S. Geological Survey Circular 844, p. 115-117. Brown, 2. D., Reilanger, R. E., Holdhal, S. R., md Balazs, E. I., 1977, Post seismic crustal ~ U f t near Anchorage, Alaska: Journal of Geophysical Research, v. 82, no. 23, p. 3369-3378. Kechadoorian, Reuben, 1968, Effects of the earthquake of March 27, 1964, on the Alaska highway system: U.S. GeologicAl Survey Professional Paper 545-C, p. C1-C66. WaCLUloch, D. S., and Bonilla, Me G., 1970, Effects of the earthquake of March 27, 1964, on the Alaska Railroad: U.S. Geological Survey Professional Paper 545-D, p. Dl-D161. Ovenshine, A. T., end Kachadoorian, Reuben, 1976, Estimate of the time required for natural regto- ration of the effects of the 1964 earthquake at Portage, In Cobb, 6. H., ed., The United States Geological Survey in Alaska: Accomplishm entc during 1975: U.S. Geological Survey Circulai 733, p. 53-54. Ovenshine, A. T., Lawson, D. E., and Bartsch-Winkler Susan, 1976, The Placer River Formation-intertidal sdimentatlon caused by the Alaska earthquake of March 27, 1964: U.S. Geological Survey Souraal of Research, v. 4, no. 2, p. 151-162. FQum 72.-Areas and Icealltie6 In southeBstern AlasKe discussed in this voltlme. A listing af autbrship, applicable figures and tables, and article pagination (in parentheses) relating to the numbered areas follows. 1, Brew and Ford, figure 19 (p. 120-124); 2, Burrell, figures 80 and 81 (p. 124-126); 3, Gehrels and others, figure 75 (p. 113-1151; 4, Gehrels and Taylor, figures 86 through 89 (p. 134-1365; 5, Hjmmelberg and others, fiwe 85 (p. 131-1341; 6, Hunt, figtires 83 and 84 (p. 128-131); 7, Karl, figures 76 and 77 (p. 115-117); 8, h and Elliott, figure 82 (p. 126-128); 9, Panuska ad ers, figure 78, tables 20 and 21 (p. 117-1~0)~ 10, !eby and others, figures 73 and 74 (p. 110-1131. l~ivision of GeolaglcaI md Lanetary WielIea, California hstftute of Technolqy, Pasadena, CA 91125.
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n Alas Accompli: ' I.S. GE OLOGI CA
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I CONTENTS Page A bst raet ........
Page 5 and 6:
-- --A I ALASEU i nued rral expluru
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........ igure .JB. ;5~ercn map ox
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. , ".,k a. ,.e ,\a 1 y U11 IIIUUII
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THE UNITED STATES GEOLOGICAL SURVEY
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~ t I r n t S i m ~ ~ Alarr a ~ man
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I -1977, RelImlnary documentat!on l
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I I MaCenn, W. R., Perez, 0. J., an
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were deslgned to impMve the accurac
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Noatak Sandstom and is overlaln con
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I (Nilsen and others, 1981a); (2) f
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I that contains the Upper Devonian
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who found Westeqaardodina sp., posb
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Table 2 lists the means rtnd for th
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' Noatak Vdley (fig. 129. This ice
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3 EUMN OF MAP UNITS WAmWARY OUAERNA
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-om displacement of the cc tween th
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I US I Surlicial dcnrrua,ts [~dater
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I Plafker, George, Hudson, Travis,
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!omlensed iring vapors generated by
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and the thinning. -upward cycles .,
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Kellum, L. B., Devless, S. N., and
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1912 sample (a mediumwey pumice blo
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various Utholagic units present Thu
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fault, and Its depositional basemen
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suggested by coplanar foUaticm and
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1 slgnlficarrtly more umnlum (73&1,
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ecrSigtallized catadastic matrix of
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analyzed to determine whether Immob
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are tgplcd of both ocean-floor basa
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& Fclsic in~rutirt rucks 0 Eio~ite
Page 67 and 68: are Lrdlcated by coexisting @&ite+q
Page 69 and 70: (Mg3.09 pe2+ 0.69 pe 0.~1~0.01~~0.9
Page 71 and 72: westward into a narrow band that ex
Page 73 and 74: EXF'lANATIOW 66600' Contan-Apprnimn
Page 75 and 76: ! few fold closures are preserved.
Page 77 and 78: even thickness and conform to irreg
Page 79 and 80: (Alnus ap.), heaths (Ericaceae, + E
Page 81 and 82: terrane extends at least 300 krn to
Page 83 and 84: Table 19.--6tneral petrography of M
Page 85 and 86: were measured on 8 12-in. mass spec
Page 87 and 88: Thin lenses of cabonate packtone to
Page 89 and 90: The cantwell(?) Pormation south of
Page 91 and 92: in the 18 lava flows b thermoremane
Page 93 and 94: Upper Cretaceous shale in contact w
Page 95 and 96: Gran tz, Arthur, 1960, Generalized
Page 97 and 98: at 15 to 20 percent. Primary Inolus
Page 99 and 100: addition, this factor generally def
Page 101 and 102: Joreskog, K. G., Klovan, J. E., and
Page 103 and 104: Mineral qItWation end r ~ k t k W e
Page 105 and 106: 1 "~_liO-/ 200 1000 B roo C E % A B
Page 107 and 108: Smaller placer mines ere active on
Page 109 and 110: Figme 62.-Plant fassils from the co
Page 111 and 112: Hallam, Anthony, 1975, Alfred Wegen
Page 113 and 114: u ALASKA Figure 65.--Sketch map of
Page 115 and 116: F ' i a?.-Intertidal bluffs compose
Page 117: C-s - - Figure 70.-Products of eros
Page 121 and 122: sampled is related to widespread ma
Page 123 and 124: marble is alsa locally present In t
Page 125 and 126: Bedding in the conglomerate ranges
Page 127 and 128: 1 purpose of this study wes to dete
Page 129 and 130: The secona k~~-~ri?tation mmes that
Page 131 and 132: epizonb'l granitic Miss, mixed with
Page 133 and 134: 40 40 Forbes, R. B., and Engels, J.
Page 135 and 136: foliated and inequigranular end con
Page 137 and 138: I I thy euheclra. Sphene anhedra an
Page 139 and 140: Quartz Alkali feldspar Plagioclase
Page 141 and 142: F'@m 85.--Sketch map of Juneau area
Page 143 and 144: HoUister, L. 8, 1966, Garnet zoning
Page 145 and 146: ! ~ bI8oO, (IN PERMIL) ~lqp~e 87.-8
Page 147 and 148: Figure 90.-Offshore ereas discussed
Page 149 and 150: Preliminerg analpsis of miemfauna f
Page 151 and 152: Survey tn Alaekai AccompUshments hh
Page 153 and 154: Gecllogical Survey Open-File Report
Page 155 and 156: I provenance, and tectonia sIgnific
Page 157 and 158: Keith, T. E. C, Barnes, Ivan, afrd
Page 159 and 160: Open-Flle Report 8P811C, 19 p. + 2
Page 161 and 162: United States Qeological Survey in
Page 163 and 164: , ,. nldslra poblisbe!d by Prior, D
Page 165 and 166: 60, Alaska: Offshore Technology Con
Page 167: Author Index [Page number underscor
Page 170 and 171:
Parks. Bruce ......................
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