3,217 research outputs found
Analysis of seismological and geological observations for moderate-size earthquakes: the Colfiorito Fault System (Central Apennines, Italy)
To contribute to the understanding of the relationships between moderate earthquakes
and the faults that are recognizable in the geological record, we analysed seismological
and geological data related to the 1997–1998 Umbria-Marche (Central Italy) earthquake
swarm. The seismological recordings, collected by local networks, allowed accurate
location of about 1000 events, whereas the geological field observations provided a picture
of the structural features and the ground-surface deformations. We also re-examined
and used some published data and results, mostly about the fault plane solutions and
the geology.
On the basis of earthquake locations, fault plane solutions, and geological mapping
we explored the possible correlation between the earthquake causative fault planes and
the normal faults exposed in the area. Our results show that the two main shocks that
occurred on 1997 September 26 (MW=5.7 and MW=6.0) originated on the same
structure, reactivating at depth the Colfiorito normal faults. Neither rupture propagated
up to the ground surface, but both triggered gravitational sliding that occurred along
pre-existing fault scarps. The earthquake that occurred on 1997 October 14 (MW=5.6)
originated on another fault branch at a much shallower depth. In spite of its lower
magnitude, this earthquake produced tectonic ruptures where the fault plane projects
to the surface in an area where no faults were previously mapped.
By comparing the palaeostress reconstruction, based on slickenside lineation analysis,
and the focal mechanism solutions, we suggest a possible correlation between the longterm
(Early Middle Pleistocene) cumulative effects of the Colfiorito Fault System
and the short-term behaviour of the fault planes observed during this earthquake
swarm, favouring the idea of a seismogenic source producing clustered moderate-size
earthquakes rather than large events scattered in time
Deliverable # 3.01.5 Results of tectonic validation for the seismogenic source model (DISS)
This deliverable materializes the results obtained in the Activity A3 that aims at a quantitative tectonic validation of the seismic source model contained in the DISS, version 3.1.0 (Basili et., 2008; DISS Working Group, 2009). The validation consists of three tests: 1) geometric; 2) kinematic; and 3) dynamic
Migration and shortening rates in the Apennines
Is compression across the northern Apennine fold-and-thrust system (Italy) still active? To address this question, we quantified the long-term rates of migration and shortening of the system along with the measurement errors. Our approach integrates structural geology, seismicity patterns, and statistical
treatment of tectonic activity. On the basis of recently published surface and subsurface data, we found a migration rate of 8.85 ± 0.61 mm/yr. The inception age of individual
fold structures follow closely this average rate, indicating that the system has been migrating at a constant rate for the past
17 Myr. Cumulative shortening of the system also increases linearly through time at 2.93 ± 0.31 mm/yr. The location of the youngest structures in the easternmost portion of the
system coincides with a significant peak of seismic moment released by historical earthquakes. We conclude that not only
these easternmost thrusts are still active, but also that they generate earthquakes
Surface abundances of ON stars
Massive stars burn hydrogen through the CNO cycle during most of their
evolution. When mixing is efficient, or when mass transfer in binary systems
happens, chemically processed material is observed at the surface of O and B
stars. ON stars show stronger lines of nitrogen than morphologically normal
counterparts. Whether this corresponds to the presence of material processed
through the CNO cycle or not is not known. Our goal is to answer this question.
We perform a spectroscopic analysis of a sample of ON stars with atmosphere
models. We determine the fundamental parameters as well as the He, C, N, and O
surface abundances. We also measure the projected rotational velocities. We
compare the properties of the ON stars to those of normal O stars. We show that
ON stars are usually helium-rich. Their CNO surface abundances are fully
consistent with predictions of nucleosynthesis. ON stars are more chemically
evolved and rotate - on average - faster than normal O stars. Evolutionary
models including rotation cannot account for the extreme enrichment observed
among ON main sequence stars. Some ON stars are members of binary systems, but
others are single stars as indicated by stable radial velocities. Hence, mass
transfer is not a simple explanation for the observed chemical properties. We
conclude that ON stars show extreme chemical enrichment at their surface,
consistent with nucleosynthesis through the CNO cycle. Its origin is not clear
at present.Comment: 18 pages, 10 figures (+ appendix). A&A accepte
Optical Spectroscopy of X-Mega targets in the Carina Nebula - VI. FO 15: a new O-Type double-lined eclipsing binary
We report the discovery of a new O-type double-lined spectroscopic binary
with a short orbital period of 1.4 days. We find the primary component of this
binary, FO 15, to have an approximate spectral type O5.5Vz, i.e. a
Zero-Age-Main-Sequence star. The secondary appears to be of spectral type
O9.5V. We have performed a numerical model fit to the public ASAS photometry,
which shows that FO 15 is also an eclipsing binary. We find an orbital
inclination of ~ 80 deg. From a simultaneous light-curve and radial velocity
solution we find the masses and radii of the two components to be 30 +/- 1 and
16 +/- 1 solar masses and 7.5 +/- 0.5 and 5.3 +/- 0.5 solar radii. These radii,
and hence also the luminosities, are smaller than those of normal O-type stars,
but similar to recently born ZAMS O-type stars. The absolute magnitudes derived
from our analysis locate FO 15 at the same distance as Eta Carinae. From
Chandra and XMM X-ray images we also find that there are two close X-ray
sources, one coincident with FO 15 and another one without optical counterpart.
This latter seems to be a highly variable source, presumably due to a
pre-main-sequence stellar neighbour of FO 15.Comment: 11 pages, 9 figures, 3 tables. Accepted for publication in MNRAS.
Higher resolution version available at
http://lilen.fcaglp.unlp.edu.ar/papers2006.htm
Thresholds for the formation of satellites in two-dimensional vortices
Copyright © 2008 Cambridge University Press. Published version reproduced with the permission of the publisher.This paper examines the evolution of a two-dimensional vortex which initially consists of an axisymmetric monopole vortex with a perturbation of azimuthal wavenumber m = 2 added to it. If the perturbation is weak, then the vortex returns to an axisymmetric state and the non-zero Fourier harmonics generated by the perturbation decay to zero. However, if a finite perturbation threshold is exceeded, then a persistent nonlinear vortex structure is formed. This structure consists of a coherent vortex core with two satellites rotating around it.
The paper considers the formation of these satellites by taking an asymptotic limit in which a compact vortex is surrounded by a weak skirt of vorticity. The resulting equations match the behaviour of a normal mode riding on the vortex with the evolution of fine-scale vorticity in a critical layer inside the skirt. Three estimates of inviscid thresholds for the formation of satellites are computed and compared: two estimates use qualitative diagnostics, the appearance of an inflection point or neutral mode in the mean profile. The other is determined quantitatively by solving the normal mode/critical-layer equations numerically. These calculations are supported by simulations of the full Navier–Stokes equations using a family of profiles based on the tanh function
A Tuned and Scalable Fast Multipole Method as a Preeminent Algorithm for Exascale Systems
Among the algorithms that are likely to play a major role in future exascale
computing, the fast multipole method (FMM) appears as a rising star. Our
previous recent work showed scaling of an FMM on GPU clusters, with problem
sizes in the order of billions of unknowns. That work led to an extremely
parallel FMM, scaling to thousands of GPUs or tens of thousands of CPUs. This
paper reports on a a campaign of performance tuning and scalability studies
using multi-core CPUs, on the Kraken supercomputer. All kernels in the FMM were
parallelized using OpenMP, and a test using 10^7 particles randomly distributed
in a cube showed 78% efficiency on 8 threads. Tuning of the
particle-to-particle kernel using SIMD instructions resulted in 4x speed-up of
the overall algorithm on single-core tests with 10^3 - 10^7 particles. Parallel
scalability was studied in both strong and weak scaling. The strong scaling
test used 10^8 particles and resulted in 93% parallel efficiency on 2048
processes for the non-SIMD code and 54% for the SIMD-optimized code (which was
still 2x faster). The weak scaling test used 10^6 particles per process, and
resulted in 72% efficiency on 32,768 processes, with the largest calculation
taking about 40 seconds to evaluate more than 32 billion unknowns. This work
builds up evidence for our view that FMM is poised to play a leading role in
exascale computing, and we end the paper with a discussion of the features that
make it a particularly favorable algorithm for the emerging heterogeneous and
massively parallel architectural landscape
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