1,152 research outputs found
The 25 October 2010 Mentawai tsunami earthquake (M_w 7.8) and the tsunami hazard presented by shallow megathrust ruptures
The 25 October 2010 Mentawai, Indonesia earthquake (M_w 7.8) ruptured the shallow portion of the subduction zone seaward of the Mentawai islands, off-shore of Sumatra, generating 3 to 9 m tsunami run-up along southwestern coasts of the Pagai Islands that took at least 431 lives. Analyses of teleseismic P, SH and Rayleigh waves for finite-fault source rupture characteristics indicate âŒ90 s rupture duration with a low rupture velocity of âŒ1.5 km/s on the 10° dipping megathrust, with total slip of 2â4 m over an âŒ100 km long source region. The seismic moment-scaled energy release is 1.4 Ă 10^(â6), lower than 2.4 Ă 10^(â6) found for the 17 July 2006 Java tsunami earthquake (M_w 7.8). The Mentawai event ruptured up-dip of the slip region of the 12 September 2007 Kepulauan earthquake (M_w 7.9), and together with the 4 January 1907 (M 7.6) tsunami earthquake located seaward of Simeulue Island to the northwest along the arc, demonstrates the significant tsunami generation potential for shallow megathrust ruptures in regions up-dip of great underthrusting events in Indonesia and elsewhere
Constraining melt geometries beneath the Afar Depression, Ethiopia from teleseismic receiver functions: the anisotropic H-Îș stacking technique
Understanding the nature of the crust has long been a goal for seismologists when imaging the Earth. This is particularly true in volcanic regions where imaging melt storage and migration can have important implications for the size and nature of an eruption. Receiver functions and the H-Îș stacking (HÎș) technique are often used to constrain crustal thickness (H) and the ratio of P to S wave velocities (Îș). In this paper, I show that it is essential to consider anisotropy when performing HÎș. I show that in a medium with horizontally transverse isotropy a strong variation in Îș with back azimuth is present, which characterizes the anisotropic medium. In a vertically transverse isotropic medium, no variation in Îș with back azimuth is observed, but Îș is increased across all back azimuths. Thus, estimates of Îș are more difficult to relate to composition than previously thought. I extend these models to melt-induced anisotropy and show that similar patterns are observed, but with more significant variations and increases in Îș. Based on these observations, I develop a new anisotropic H-Îș stacking technique which inverts HÎș data for melt fraction, aspect ratio, and orientation of melt inclusions. I apply this to data for the Afar Depression and show that melt is stored in interconnected stacked sills in the lower crust, which likely supply the recent volcanic eruptions and dike intrusions. This new technique can be applied to any anisotropic medium where it can provide constraints on the average crustal anisotropy
Mesons from global Anti-de Sitter space
In the context of gauge/gravity duality, we study both probe D7-- and probe
D5--branes in global Anti-de Sitter space. The dual field theory is N=4 theory
on R x S^3 with added flavour. The branes undergo a geometrical phase
transition in this geometry as function of the bare quark mass m_q in units of
1/R with R the S^3 radius. The meson spectra are obtained from fluctuations of
the brane probes. First, we study them numerically for finite quark mass
through the phase transition. Moreover, at zero quark mass we calculate the
meson spectra analytically both in supergravity and in free field theory on R x
S^3 and find that the results match: For the chiral primaries, the lowest level
is given by the zero point energy or by the scaling dimension of the operator
corresponding to the fluctuations, respectively. The higher levels are
equidistant. Similar results apply to the descendents. Our results confirm the
physical interpretation that the mesons cannot pair-produce any further when
their zero-point energy exceeds their binding energy.Comment: 43 pages, 8 figures, references edited, few typos corrected, updated
to match the published versio
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An S to P Converted Phase Recorded Near Long Valley/Mono Craters Region, California
We examine and model the arrival time of a large secondary seismic arrival recorded in the Long Valley/Mono Craters region of east-central California. Zucca et. al. (1987) and Peppin (1987) both previously reported on different features of this same arrival. Using both arrays of sources and receivers we demonstrate that the arrival is an S to P converted phase as first suggested by Lewis and Peppin (1988). Backprojection of the observed travel times allows us to constrain the location of the converting material to a southeast dipping zone between 7 and 16 km depth, and {+-} 5 km on either side of the topographic margin of the caldera. The analysis demonstrates the power of source and receiver array combinations when analyzing seismic arrivals in complicated environments
Holographic Flavor Transport in Arbitrary Constant Background Fields
We use gauge-gravity duality to compute a new transport coefficient
associated with a number Nf of massive N=2 supersymmetric hypermultiplet fields
propagating through an N=4 SU(Nc) super-Yang-Mills theory plasma in the limits
of large Nc and large 't Hooft coupling, with Nf << Nc. We introduce a baryon
number density as well as arbitrary constant electric and magnetic fields,
generalizing previous calculations by including a magnetic field with a
component parallel to the electric field. We can thus compute all components of
the conductivity tensor associated with transport of baryon number charge,
including a component never before calculated in gauge-gravity duality. We also
compute the contribution that the flavor degrees of freedom make to the
stress-energy tensor, which exhibits divergences associated with the rates of
energy and momentum loss of the flavor degrees of freedom. We discuss two
currents that are free from these divergences, one of which becomes anomalous
when the magnetic field has a component parallel to the electric field and
hence may be related to recent study of charge transport in the presence of
anomalies.Comment: 27 page
Mantle Transition Zone Discontinuities beneath the Contiguous United States
Using over 310,000 high-quality radial receiver functions recorded by the USArray and other seismic stations in the contiguous United States, the depths of the 410 km and 660 km discontinuities (d410 and d660) are mapped in over 1,000 consecutive overlapping circles with a radius of 1â°. The average mantle transition zone (MTZ) thickness for both the western and central/eastern U.S. is within 3 km from the global average of 250 km, suggesting an overall normal MTZ temperature beneath both areas. The Pacific Coast Ranges and the southern Basin and Range Province are underlain by a depressed d410, indicating higher-than-normal temperature in the upper MTZ. The proposed Yellowstone and Raton hot spots are not associated with clear undulations of the MTZ discontinuities, but d410 beneath another proposed hot spot, Bermuda, is depressed significantly and d660 has a normal depth. Low-temperature regions are found in the upper MTZ associated with the subducted Juan de Fuca slab beneath the northern Rocky Mountains and in two circular areas beneath the northern Basin and Range Province and the southern Colorado Plateau. Part of the Great Plains is characterized by a depressed d660. This observation, when combined with results from seismic tomography, suggests the existence of a cold region in the lower MTZ, probably associated with subducted Farallon slab segments
Doped two orbital chains with strong Hund's rule couplings - ferromagnetism, spin gap, singlet and triplet pairings
Different models for doping of two-orbital chains with mobile
fermions and strong, ferromagnetic (FM) Hund's rule couplings stabilizing the
S=1 spins are investigated by density matrix renormalization group (DMRG)
methods. The competition between antiferromagnetic (AF) and FM order leads to a
rich phase diagram with a narrow FM region for weak AF couplings and strongly
enhanced triplet pairing correlations. Without a level difference between the
orbitals, the spin gap persists upon doping, whereas gapless spin excitations
are generated by interactions among itinerant polarons in the presence of a
level difference. In the charge sector we find dominant singlet pairing
correlations without a level difference, whereas upon the inclusion of a
Coulomb repulsion between the orbitals or with a level difference, charge
density wave (CDW) correlations decay slowest. The string correlation functions
remain finite upon doping for all models.Comment: 9pages, 9figure
Origin of Spin Incommensurability in Hole-doped S=1 Chains
Spin incommensurability has been recently experimentally discovered in the
hole-doped Ni-oxide chain compound (G. Xu {\it
al.}, Science {\bf 289}, 419 (2000)). Here a two orbital model for this
material is studied using computational techniques. Spin IC is observed in a
wide range of densities and couplings. The phenomenon originates in
antiferromagnetic correlations ``across holes'' dynamically generated to
improve hole movement, as it occurs in the one-dimensional Hubbard model and in
recent studies of the two-dimensional extended t-J model. The close proximity
of ferromagnetic and phase-separated states in parameter space are also
discussed.Comment: RevTex, 4 pages, 4 figures (eps
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