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
Study Area Year 3
Bo rde r
Y
56 -160
Co ok In
-156
PWS
Kenai Penin.
Study Area Year 1
Flt
.Sy s.
Y’ Gulf of Alaska
Kodiak Island
-152
ut ia n
Tr en ch
B R FS
Pe ni n.
58
A la sk a
latitude
60
Ra ng es
A le
Alaska
let
62
Study Area Year 2
-148
-144
-140
longitude
Red is BRFS. Boxes show study areas for years 1,2 and 3. Black square indicates Anchorage. Interpretation of YY’ shown in last figure.
62 Border Ranges Fault System Other faults and folds
61.75
61.5
gravity data collected 2011 gravity data collected 2010 gravity data collected June 2009 gravity data collected March 2009
61.25
original gravity data base
61
60.75
60.5
60.25 -151.5
-151
-150.5
-150
-149.5
-149
-148.5
Between 2009 and 2011 we have collected over 1200 gravity observations (green, magenta, blue, and black symbols) to help constrain our models of the BRFS. Note sparseness of original data (brown plusses).
Border Ranges Fault System Other faults and folds Gravity observation
62
61.75
60 40 20
61.5
0 -20
61.25
-40 -60
61
-80 -100 -120
60.75
-140 -160 free air gravity in mGals
60.5
60.25 -151.5
-151
-150.5
-150
-149.5
-149
-148.5
Our latest map of variation in gravitational acceleration across the BRFS.
We have collected gravity observations in subregions to estimate variations in nearsurface densities. These are comparable to estimates from well logs (blue box) or surface samples (red box).
Cross section along Y-Y’ (see first figure) showing observed gravity (black dots), calculated gravity (black line) and error (red line). Preliminary geologic/density model shown below. Model is based on well log, seismic reflection, surface geology and other information.
