Jökull - 01.01.2015, Side 54

J. Schuler et al.,
Þeistareykir
Kraa
Fremri −
námar
Askja
HFFS
BLAF
BRUN
BUNG
BURF
DDAL
DRUM
FJAS
FLAT
GUDF
HRUR
HVAN
K006 K008
K190
KODA
KOLL
KVIH
MIDF
MYVO
N66D
SBLA
SKOG
SVAD
TREB
VEGG
VVAT
K009
K010
K180
VIKI
HOTTOSKV UTYR
DIM
GHA
KVO
MEL
REN
SKI
GHS
0 10
km
0 20 40 60 80
E p ic e n t r a l d is t a n c e [ k m ]
0
5
10
15
20
25
T
ra
v
e
l
ti
m
e
[
s
]
VI
KI
VV
AT
N
66
D
G
U
D
F
BU
N
G
G
H
A
KV
IH
K0
08
K0
30
K0
06
K0
55
K1
90
K2
19
K2
50
BU
RF
H
VA
N
SK
O
G
TR
EB
BL
AF
KO
D
A
VE
G
G
KO
LL
FL
AT
H
RU
R
M
YV
O
SV
AD
D
D
AL
M
ID
F
FJ
AS...
0 2 0 4 0 6 0 8 0
E p ic e n t r a l d is t a n c e [ k m ]
0
5
10
15
20
25
T
ra
v
e
l
ti
m
e
[
s
]
VI
KI
VV
AT
N
66
D
G
U
D
F
BU
N
G
G
H
A
KV
IH
K0
08
K0
30
K0
06
K0
55
K1
90
K2
19
K2
50
BU
RF
H
VA
N
SK
O
G
TR
EB
BL
AF
KO
D
A
VE
G
G
KO
LL
FL
AT
H
RU
R
M
YV
O
SV
AD
D
D
AL
M
ID
F
FJ
AS...
66°00'
-20
-20
65°45'
65°30'
65°15'
-17°00' -16°30'
a)
b)
c)
SouthNorth
North South
Figure 2. Example seismograms of event 2012 Jan 24 20:49:52.85, ML=0.67 based on SIL stations, located
at about 16–17 km depth b.s.l., showing a) vertical and b) horizontal components. The traces were zero-phase
band-pass filtered between 1–10 Hz. P-wave (red) and S-wave (green) first arrivals are often best observed on
the vertical and horizontal components, respectively. Seismic energy (orange) arriving after the S-wave first
breaks, best visible in the northern direction, may be interpreted as SmS arrivals with their reflector (the Moho)
at approximately 6 km below the hypocenter. A total of 35 P- and S-wave arrival pairs were picked. c) Map of
the stations (triangles) in our network along the NVZ and the epicenter (green circle) of the source event from
which these seismograms come. Mapped faults of the Húsavík-Flatey system (HFFS) are shown in red color and
the faults of the Þeistareykir fissure swarm in purple, after Magnúsdóttir and Brandsdóttir (2011). – Jarðskjálfti
suðaustan Þeistareykja 24. janúar 2012, kl. 20:49, stærð ML=0.67 samkvæmt SIL-mælistöðvum. Skjálftinn
hafði upptök á 16–17 km dýpi. Samsett línurit af lóðréttum a) og láréttum b) þætti hreyfingarinnar á skjálfta-
mælistöðvum á mynd (c). Upptök skjáfltans eru merkt með grænfylltum hring á kortinu. Misgengi Húsavíkur-
Flateyjarbeltisins eru rauð og misgengi sprungusveims Þeistareykja lillablá (Magnúsdóttir og Brandsdóttir,
2011). Rauð brotalína sýnir komutíma P-bylgjunnar sem er skýrust á a) og græn brotalína komutíma S-bylgj-
unnar, sem er skýrust á (b). Reiknaður komutími SmS-bylgju frá botni skorpunnar (appelsínugul lína), 6 km
fyrir neðan upptök skjálftans, passar þokkalega vel við aukið útslag á lárétta línuritinu b) og gefur til kynna
23–24 km jarðskorpuþykkt á þessu svæði.
Including only earthquakes with P- or S-wave ar-
rivals recorded at a minimum of five nearby stations,
the remaining 153 events were then used in the VE-
LEST algorithm by Kissling et al. (1994) to simul-
taneously build a 1D velocity model and locate the
hypocenters. An average local P- to S-wave veloc-
ity (Vp/Vs) ratio of 1.78 was estimated from Wadati
diagrams using data presented here. As starting ve-
locities we used the Krafla regional model and the
South Iceland Lowland (SIL) model (Stefánsson et
al., 1993), routinely used by IMO for earthquake lo-
cation across Iceland. Both models and other tested
velocity-depth profiles, displayed in Figure 3a, were
examined to find a simple 1D model fitting our lim-
ited dataset. The velocity profile we obtained (Table
1) is weakly constrained where we have a poor dis-
54 JÖKULL No. 65, 2015