Geology Reference
In-Depth Information
especially in the upper mantle. The technique of
determining the lateral variations of seismic ve-
locity starting from the observation of arrival time
differences is known as
seismic tomography
and
represents a powerful tool of modern seismology.
This technique has shown to be effective in pro-
viding spectacular images of the Earth's internal
structure, in particular of descending slabs.
local travel time table for
Pg
waves generated
from a surficial source, assuming take-off an-
gles from 85
ı
to the minimum take-off angle
for
Pg
waves, with increments of 5
ı
, starting
from (
9.60
)and(
9.61
).
References
Aki K (1969) Analysis of seismic coda of local earth-
quakes as scattered waves. J Geophys Res 74:615-631.
Anderson DL, Spetzler H (1970) Partial melting and the
low-velocity zone. Phys Earth Planet Int 4(1):62-64
Dziewonski AM, Anderson DL (1981) Preliminary ref-
erence
Problems
1. What is the geometry of a seismic ray with
™
0
D
0?;
2. Determine the travel-time curve
T
D
T
(
X
)for
waves reflected at a horizontal discontinuity,
knowing that the two-way travel time (TTWT)
for vertical incidence is
T
0
;
3. What is the correction that must be applied
on a set of travel times of reflected arrivals
to obtain proportionality between arrival time
and depth to the reflector (this is known as
normal moveout
)?
4. Determine the travel-time curve
T
D
T
(
X
)of
a
Pn
phase, given the crustal thickness and
assuming a homogeneous crust and surficial
source;
5. Assuming a homogeneous crustal layer, the
first arrival at short range would be a direct
wave only below the crossover distance. De-
termine this distance;
6. Determine the critical distance below which
Pn
phase arrivals are impossible, assuming a
homogeneous crust;
7. Draw the delay time curve associated with the
travel time curve of Fig.
9.13
;
8. Download the MS Excel file ESP215.txt, con-
taining a velocity model of oceanic crust in the
Balearic Basin (Pascal et al., 1993,
Geophys.
J. Int.,
113
, 701-726.), from the supplemental
material web site. This file contains a table that
divides the oceanic crust into a series of flat
layers with
P
wave velocity that increases lin-
early and variable thickness. Write a computer
program that uses this ASCII table to build the
Earth
model.
Phys
Earth
Planet
Inter
25:
297-356
Hirschmann MM (2010) Partial melt in the oceanic low
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Jeffreys H, Bullen KE (1940) Seismological tables, British
Association for the Advancement of Science. Burling-
ton House, London
Karato SI, Jung H (1998) Water, partial melting and the
origin of the seismic low velocity and high attenuation
zone in the upper mantle. Earth Planet Sci Lett 157
(3-4):193-207
Kennett BLN, Engdahl ER (1991) Travel times for global
earthquake location and phase identification. Geophys
J Int 105:429-466
Kennett BLN, Engdahl ER, Buland R (1995) Constraints
on seismic velocities in the Earth from traveltimes.
Geophys J Int 122:108-124
Lambert IB, Wyllie PJ (1970) Low-velocity zone of the
Earth's mantle: incipient melting caused by water.
Science 169(3947):764-766
Sato H, Fehler MC, Maeda T (2012) Seismic wave
propagation and scattering in the heterogeneous Earth.
Springer, Berlin, p 494
Shearer PM (2007) Seismic scattering in the deep Earth.
In: Schubert G (ed) Treatise on geophysics, vol 1.
Elsevier, The Netherlands, pp 695-730
Shearer PM (2009) Introduction to seismology, 2nd edn.
Cambridge University Press, Cambridge, UK, 396 pp
Stein S, Wysession M (2003) An Introduction to seis-
mology, earthquakes, and earth structure. Blackwell
Publishing Ltd, Carlton, 498 pp
Stixrude L, Lithgow-Bertelloni C (2005) Mineralogy and
elasticity of the oceanic upper mantle: origin of the
low-velocity zone. J Geophys Res 110(B3):B03204.
doi:
10.1029/2004JB002965
Storchak DA, Schweitzer J, Bormann P (2003) The
IASPEI standard seismic phase list. Seismol Res Lett
74(6):761-772
Thybo H (2006) The heterogeneous upper mantle low
velocity zone. Tectonophysics 416(1):53-79
