679 research outputs found
Source process and tectonic implications of the great 1975 North Atlantic earthquake
The Atlantic segment of the Africa–Europe plate boundary has usually been interpreted as a transform boundary on the basis of the bathymetric expression of the Gloria fault and dextral strike-slip first-motion mechanisms aligned along the Azores–Gibraltar line of seismicity. The 1975 May 26 earthquake ( M s =7.9) was assumed to fit into this framework because it occurred in the general area of this line and has a similar first-motion focal mechanism (strike=288°, dip=72°, slip angle=184°). However, several anomalies cast doubt on this picture: the event is abnormally large for an oceanic transform event; a sizeable tsunami was excited; the aftershock area is unusually small for such a large event; and most significantly, the epicentre is 200 km south of the presumed plate boundary. The Rayleigh wave radiation pattern indicates a change in focal mechanism to one with a significant dip-slip component. The short duration of the source time history (20 s, as deconvolved from long-period P -waves), the lack of directivity in the Rayleigh waves, and the small one-day aftershock area suggest a fault length less than 80 km. One nodal plane of the earthquake is approximately aligned with the trace of an ancient fracture zone. We have compared the Pasadena 1-90 record of the 1975 earthquake to that of the 1941 North Atlantic strike-slip earthquake (200 km to the NNW) and confirmed the large size of the 1941 event ( M =8.2). The non-colinear relationship of the 1975 and 1941 events suggests that there is no well-defined plate boundary between the Azores and Gibraltar. This interpretation is supported by the intraplate nature of both the 1975 event and the large 1969 thrust event 650 km to the east. This study also implies that the largest oceanic strike-slip earthquakes occur in old lithosphere in a transitional tectonic regime.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/72996/1/j.1365-246X.1985.tb05148.x.pd
Uplift and subsidence associated with the great Aceh-Andaman earthquake of 2004
Rupture of the Sunda megathrust on 26 December 2004 produced broad regions of uplift and subsidence. We define the pivot line separating these regions as a first step in defining the lateral extent and the downdip limit of rupture during that great M_w ≈ 9.2 earthquake. In the region of the Andaman and Nicobar islands we rely exclusively on the interpretation of satellite imagery and a tidal model. At the southern limit of the great rupture we rely principally on field measurements of emerged coral microatolls. Uplift extends from the middle of Simeulue Island, Sumatra, at ~2.5°N, to Preparis Island, Myanmar (Burma), at ~14.9°N. Thus the rupture is ~1600 km long. The distance from the pivot line to the trench varies appreciably. The northern and western Andaman Islands rose, whereas the southern and eastern portion of the islands subsided. The Nicobar Islands and the west coast of Aceh province, Sumatra, subsided. Tilt at the southern end of the rupture is steep; the distance from 1.5 m of uplift to the pivot line is just 60 km. Our method of using satellite imagery to recognize changes in elevation relative to sea surface height and of using a tidal model to place quantitative bounds on coseismic uplift or subsidence is a novel approach that can be adapted to other forms of remote sensing and can be applied to other subduction zones in tropical regions
Recommended from our members
Influences on Affiliate HRM Systems in Japanese MNCs in Southeast Asia
Using data from 160 Asian affiliates of American and Japanese MNCs, this paper explores the determinants of whether MNCs transfer their parent company HRM systems overseas or adopt local practices. We find that demographic predictor variables which have often been found in previous studies to predict similarity are relatively unimportant while perceived HRM competence of the MNC is an important determinant of HRM transfer
Risk of Depression in Persons With alzheimer\u27s Disease: a National Cohort Study
INTRODUCTION: Depression is a risk factor and possible prodromal symptom of Alzheimer\u27s disease (AD), but little is known about subsequent risk of developing depression in persons with AD.
METHODS: National matched cohort study was conducted of all 129,410 persons diagnosed with AD and 390,088 with all-cause dementia during 1998-2017 in Sweden, and 3,900,880 age- and sex-matched controls without dementia, who had no prior depression. Cox regression was used to compute hazard ratios (HRs) for major depression through 2018.
RESULTS: Cumulative incidence of major depression was 13% in persons with AD and 3% in controls. Adjusting for sociodemographic factors and comorbidities, risk of major depression was greater than two-fold higher in women with AD (HR, 2.21; 95% confidence interval [CI], 2.11-2.32) or men with AD (2.68; 2.52-2.85), compared with controls. Similar results were found for all-cause dementia.
DISCUSSION: Persons diagnosed with AD or related dementias need close follow-up for timely detection and treatment of depression.
HIGHLIGHTS: In a large cohort, women and men with AD had \u3e2-fold subsequent risk of depression.Risks were highest in the first year (\u3e3-fold) but remained elevated ≥3 years later.Risk of depression was highest in persons aged ≥85 years at AD diagnosis.Persons with AD need close follow-up for detection and treatment of depression
Sum-over-states vs quasiparticle pictures of coherent correlation spectroscopy of excitons in semiconductors; femtosecond analogues of multidimensional NMR
Two-dimensional correlation spectroscopy (2DCS) based on the nonlinear
optical response of excitons to sequences of ultrafast pulses, has the
potential to provide some unique insights into carrier dynamics in
semiconductors. The most prominent feature of 2DCS, cross peaks, can best be
understood using a sum-over-states picture involving the many-body eigenstates.
However, the optical response of semiconductors is usually calculated by
solving truncated equations of motion for dynamical variables, which result in
a quasiparticle picture. In this work we derive Green's function expressions
for the four wave mixing signals generated in various phase-matching directions
and use them to establish the connection between the two pictures. The formal
connection with Frenkel excitons (hard-core bosons) and vibrational excitons
(soft-core bosons) is pointed out.Comment: Accepted to Phys. Rev.
Highly Variable Recurrence of Tsunamis In the 7,400 Years Before the 2004 Indian Ocean Tsunami
The devastating 2004 Indian Ocean tsunami caught millions of coastal residents and the scientific community off-guard. Subsequent research in the Indian Ocean basin has identified prehistoric tsunamis, but the timing and recurrence intervals of such events are uncertain. Here we present an extraordinary 7,400 year stratigraphic sequence of prehistoric tsunami deposits from a coastal cave in Aceh, Indonesia. This record demonstrates that at least 11 prehistoric tsunamis struck the Aceh coast between 7,400 and 2,900 years ago. The average time period between tsunamis is about 450 years with intervals ranging from a long, dormant period of over 2,000 years, to multiple tsunamis within the span of a century. Although there is evidence that the likelihood of another tsunamigenic earthquake in Aceh province is high, these variable recurrence intervals suggest that long dormant periods may follow Sunda megathrust ruptures as large as that of the 2004 Indian Ocean tsunami
Reduction of CO_2 by Pyridine Monoimine Molybdenum Carbonyl Complexes: Cooperative Metal–Ligand Binding of CO_2
[(^(Ar)PMI)Mo(CO)_4] complexes (PMI=pyridine monoimine; Ar=Ph, 2,6-di-iso-propylphenyl) were synthesized and their electrochemical properties were probed with cyclic voltammetry and infrared spectroelectrochemistry (IR-SEC). The complexes undergo a reduction at more positive potentials than the related [(bipyridine)Mo(CO)_4] complex, which is ligand based according to IR-SEC and DFT data. To probe the reaction product in more detail, stoichiometric chemical reduction and subsequent treatment with CO_2 resulted in the formation of a new product that is assigned as a ligand-bound carboxylate, [(^(iPr2Ph)PMI)Mo(CO)_3(CO_2)]^(2-), by NMR spectroscopic methods. The CO_2 adduct [(^(iPr2Ph)PMI)Mo(CO)_3(CO_2)]^(2-) could not be isolated and fully characterized. However, the C_C coupling between the CO_2
molecule and the PDI ligand was confirmed by X-ray crystallographic characterization of one of the decomposition products of [(^(iPr2Ph)PMI)Mo(CO)_3(CO_2)])^(2-)
Near-field propagation of tsunamis from megathrust earthquakes
We investigate controls on tsunami generation and
propagation in the near-field of great megathrust earthquakes
using a series of numerical simulations of subduction and
tsunamigenesis on the Sumatran forearc. The Sunda
megathrust here is advanced in its seismic cycle and may be
ready for another great earthquake. We calculate the seafloor
displacements and tsunami wave heights for about 100
complex earthquake ruptures whose synthesis was informed
by reference to geodetic and stress accumulation studies.
Remarkably, results show that, for any near-field location:
(1) the timing of tsunami inundation is independent of slipdistribution
on the earthquake or even of its magnitude, and
(2) the maximum wave height is directly proportional to the
vertical coseismic displacement experienced at that location.
Both observations are explained by the dominance of long
wavelength crustal flexure in near-field tsunamigenesis. The
results show, for the first time, that a single estimate of vertical
coseismic displacement might provide a reliable short-term
forecast of the maximum height of tsunami waves
Optically induced coherent intra-band dynamics in disordered semiconductors
On the basis of a tight-binding model for a strongly disordered semiconductor
with correlated conduction- and valence band disorder a new coherent dynamical
intra-band effect is analyzed. For systems that are excited by two, specially
designed ultrashort light-pulse sequences delayed by tau relatively to each
other echo-like phenomena are predicted to occur. In addition to the inter-band
photon echo which shows up at exactly t=2*tau relative to the first pulse, the
system responds with two spontaneous intra-band current pulses preceding and
following the appearance of the photon echo. The temporal splitting depends on
the electron-hole mass ratio. Calculating the population relaxation rate due to
Coulomb scattering, it is concluded that the predicted new dynamical effect
should be experimentally observable in an interacting and strongly disordered
system, such as the Quantum-Coulomb-Glass.Comment: to be published in Physical Review B15 February 200
Future Seismic Hazards in Southern California - Phase I: Implications of the 1992 Landers Earthquake Sequence
Southern California and its seismologists received a wake-up call on June 28, 1992. The
largest earthquake to strike southern California in 40 years occurred near the town of Landers,
located 30 km north of the San Andreas fault. It had a magnitude of 7.5 (M7.5). Three and one-half
hours later, a M6.5 aftershock struck the Big Bear area 40 km (kilometers) to the west of
Landers. An ad hoc working group was rapidly convened in July, 1992, to evaluate how the
Landers-Big Bear earthquake sequence might affect future large earthquakes along major faults
in southern California. In particular, what are the chances of large earthquakes in the next few
years and how do they compare to previous estimates (such as those of the Working Group on
California Earthquake Probabilities -- WGCEP, 1988)? Such an evaluation was made for central
California after the Lorna Prieta earthquake of 1989 (WGCEP, 1990). The charge to the Landers
ad hoc working group included analyzing the seismicity for the last several years in southern
California and the new paleoseismic, geologic, and geodetic data recently available for southern
California. To inform the public about the potential hazard of plausible earthquakes, the working
group was also asked to map the predicted severity of ground shaking for such earthquakes
compared to that from the Landers earthquake
- …