Constraints on the Structure of the Border Ranges Fault System, South-Central Alaska from Integrated 3-D Inversion of Gravity/Magnetic Data (grant 48312-AC8) Diane Doser, Dept. Geological Sciences,Univ. Texas at El Paso
Significance • The Border Ranges Fault System (BRFS) bounds the major petroleum producing region of Cook Inlet Basin • The geometry, timing, sense and amount of movement along BRFS and its influence on basin formation are poorly known • We will test models of BRFS structure and basin evolution using a novel 3-D inversion of gravity and magnetic data
Inle t
Alaska
Bo rde r
Kenai Penin.
Ra ng es
PWS
Flt
.Sy s.
Co ok
60
56 -160
-156
FS
Tr en ch
R
n
Kodiak Island
-152
A le ut ia
la sk a
58
B
Pe ni n.
Gulf of Alaska
A
latitude
62
Study Area Year 1
-148
-144
longitude
Red is BRFS. Box is our study area for year 1.
-140
View (looking southeast) across BRFS from Kenai Lowlands to Kenai Mountains
60.75
60.5
60.25 Border Ranges Fault System Other faults and folds -151
-150.5
-150
gravity data collected March 2009 gravity data collected June 2009 original gravity data base
In the spring and summer of 2009 we collected over 500 gravity observations (green and magenta symbols) to help constrain our models of the BRFS. Note sparseness of original data (red plusses).
Setting up GPS unit in the field (required for precise location of gravity observation points)
100 80 60 40 20 0 -20 -40 -60 -80 -100 -120 -140 -160 -180 -200 grav. accel. in milligals
Border Ranges Fault System Other faults and folds Gravity observation
Our latest map of variation in gravitational acceleration across the BRFS.
We have collected closely spaced gravity observation in subregions to estimate variations in near-surface densities as indicated. Density logs from oil and gas wells will also be used to help build near-surface density models.
Second Year Tasks • Take additional gravity observations in Anchorage area to help constrain structure of northeastern Cook Inlet Basin • Complete testing of forward modeling code for magnetic data (testing of forward modeling code for gravity data is complete) • Complete and test inversion code • Test viable models of the BRFS
