n Alas - Alaska Division of Geological & Geophysical Surveys - State ...

(19811 awed that neither earthquake ruptured into
the Shumagin gap, but the evidence is circumstantial.
Strah release during 1938 (or 1946) seems at least a
possible explanation for the absence of any observed
strdn accumulation.
At Cape Yakataga, an 18-Une trllateration net-
work with e 35-km aperture was measured in 1979 and
19801 included within this network is a seotion of a
1959 dectronio distance traverse. Comparison of the
1959 and 1979-80 surveys shows that the west edge 06
the Yakataga network has been dkphced 3.4 nl S. 40
E. wlth respect to the east edge. We attribute thls
deformation primarily to the 1964 Alaska earthqualre,
the effects of which apparently penetrated into what
Is now known as the Yakataga seismic gap. A cornpar-
isan of five lengths common to the 1979 and 1980 sur-
veys shows no significant strain accumulation at the
0.5-~gtrain level.
REPEREN CES CITED
Davfes, J. N., and House, L. S., 1979, Aleutian subdue
tion zone seismicity, volcanbtrench separation,
and their relation to great thrust-type earth-
quakes: Journal of Geophysical Researoh, v. 84,
no. B9, p. 4583-4591.
Davies, J. N., Sykes, L. R., House, L. S., and Jacob, K.
H., 1981, Shumagin seismic gap, Alaska Penin-
sulas History of great earthquakes, tectonic
settlng, and evidence for high seismic potential:
Journal of Geophysical Research, v. 88, no. B5,
p. 3821-385s.
Savage, J. C., 1883, A dislocetIon model of strain
accumulation and release at a subduction zone:
Journal of Geophysical Research [tn pm.
By Rialmd 116 OUnq aad Jane8 I). Hoffman
The Anchorage geochemical field laboratory was
in operation durlng summer 1981 at 5500 Oilwell Road,
Elmendorf AFB, Alaska, as it has been sfnce 1967. The
laboratory is managed and operated by the U.8. Geo-
logical Survey, Golden, Cola. It is equipped with a
drying oven, rock crushers, pulverizers, and sleve
shakers to preparc samples of rock, stream sediment,
glacial debris, and soil for geochemical analysk. The
analytical laboratory include8 two emission spectro-
graphs capable of generating semiquantitatlve analyses
for 9 1 elements on each sample. -4tomlc-absorption
spaatrophotornetry and bercury-vapordetection
instruments com~lement the analvticd capabilities.
To provide additional space and -faafliti&, a self-
contained wet-hemical mobile unit (housed in a 7-m-
long fifth-wheel trailer) was brought to Anchorage
from Denver in 1880. A minicomputer system, added
in recent years, is used to enter, edlt, update, and
retrieve analytical data from the rock-analysis storage
system (RASS) while the laboratory is in normal. opera-
tion. This system circumvents the keypmah operation
and timelag involved in processing date through the
office in Golden.
The field laboratory offers the advantage of
central location for last mall service and is able to
handle a large volume of samples within a short
period. The quick turnaround of analytical results
allows M e r sampling or checking of anomalous or
critical meas while crews are st111 in their fteld mas.
During the 3-1/2-month pericd in 1981 when the
laboratory was in operation, about 7,000 samples col-
lected from the Mount Hayes, BristoI Bay-Ugashfk-
Karluk, Healy, Circle, Wiseman, OancUer Lake, Killik
River, Bendeleben?Solornon, Baird Mountains, and
Petersburg quadrangles and the Chugach RARE l
project area were processed. The results of these
analyses were used mainly to generate geochemical
maps that aid in mineral-resource assessments and
help locate possible mineral deposits.
Cornput-ted latitude and la@- template9
for rapid determinatloo d -hie papitiam in
Alaslca
For the put 8 years, U.S. Geological Survey
scientists worklng in Alaska have been aided by
computer-generated latitude and longitude
ternplat-. These templates were prepared by digital
computers a d are reproduced on transparent film,
which can be easily laid over maps and plotting
sheets. Vgrfous scales and formats have already been
prepared and more may become available in the
future. Reproduction problems hampered the early
distribution of the templates, and their we was
originally restricted to Government workers.
However, their popularity has shown a need tor wider
distribution, which has recently been met by improved
reproduction and distribution methods; templates are
now available to the public through specified offiaes in
Anchorage and Denver per information in the last
paragraph below. I
Geographic coordinates are an essential com-
ponent of any data base designed to show map lo=-
tions of field data, but the methods of measuring,
recording, and plotting these locations vary. Cartesian
coordinates, such as the State grid systems or univer-
sal transverse mercator (UTM) grid, are satisfactory
for plotting data within local areas, and the coordi-
nates can be measured by linear map scales. However,
cartesian systems do not provide accurate representa-
tions of locations over large areas of the Earth's
spherical surface, and so the global system of latitude
and longitude is the conventiond way of recording
geographic locations in data bases covering large
areas. Although most modern topographic maps of the
United Sates include the State grid and UTM coordi-
nates on their margins, latitudes and longitudes are
better labeled and generally include gridmark ticks
within the maps. On most map projections, meridional
convergence causes longitude scale changes that at
high latitudes can be significant even within a single
map. Digital computer programs now provide systems
for converting from gewaphic to cartesim W-
dinates and vice versa, and electronic plotters and
digitizers may be used for more accurate measurement
and pIotting of locations. Computers, however, are
expensive facilities that generally require space, el-
tric power, and significant setup time. me templetea
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