Jökull - 01.01.2010, Side 57

Upptyppingar seismic swarms
7209
7210
7211
7212
7213
7214
N
o
rt
h
in
g
[k
m
]
437
438
439
440
441
442
E
a
s
ti
n
g
[k
m
]
20Jul 12:00 21Jul 12:00 22Jul 12:00 23Jul 12:00 24Jul 12:00
13
14
15
16
17
18
D
e
p
th
[k
m
]
Date in 2007
Figure 7. Single-event locations derived from the data of six SIL stations that are common to both the ASN and SIL-system.
Locations are obtained from HypoInverse-2000 using time-pick information provided by Cambridge University from PPICK
(red) and the IMO from similar manual refinement procedures (blue). All locations are re-datumed to depth below sea level.
Due to the limited number of stations used here, the locations appear more scattered than in Figure 6; however, the offsets
in northing and depth have effectively disappeared (Table 1). – Staðsetningar stakra skjálfta með SIL-stöðvunum sex, sem
notaðar eru í báðum netum. HypoInverse-2000 er notað í báðum tilfellum og komutímaaflestrar eru þeir sömu og á 6. mynd
(PPICK og leiðréttir SIL-komutímar). Dýpið er miðað við sjávarmál í báðum tilfellum. Staðsetningarnar eru dreifðari en
áður, vegna þess hve fáar stöðvar eru notaðar, en engin kerfisbundin hliðrun er sjáanleg.
best-fit plane to each case, respectively. We have ig-
nored events that locate below 17.5 km depth, as they
do not seem to be associated with the dyke itself.
These events are most apparent in Figure 11. The
distribution of the hypocentres looking from the dip
direction of the best-fit plane to the ASN relative lo-
cations is shown in Figure 12.
Two standard-deviation (2σ) relative location un-
certainties for ASN are estimated as < 60 m, based
on the output of HypoDD (Waldhauser, 2001), which
computes errors using the method of singular value
decomposition. Relative uncertainties for SIL are es-
timated as < 400 m by Jakobsdóttir et al. (2008);
however, when SIL system time picks are applied
through HypoDD for consistency with our own error
estimates, we obtain relative location uncertainties of
<120 m. Absolute horizontal and vertical uncertain-
ties for the SIL catalogue locations are estimated as
±0.7 km and ±1.0 km (1σ), respectively (Slunga et
al., 1995).
The best-fit plane to the ASN data dips at
49.2◦±0.2◦ (2σ) and strikes at N075◦E±1◦. For SIL,
relative locations of identical events are best repre-
sented by a plane dipping at 45.6◦±2.6◦ and striking
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