Recurrent intraplate tectonism in the new madrid seismic zone

For the first time, New Madrid seismicity can be linked to specific structural features that have been reactivated through geologic time. Extensive seismic reflection profiling reveals major faults coincident with the main earthquake trends in the area and with structural deformation apparently caused by repeated episodes of igneous activity.     

Rapid intraplate strain accumulation in the new madrid seismic zone

Remeasurement of a triangulation network in the southern part of the New Madrid seismic zone with the Global Positioning System has revealed rapid crustal strain accumulation since the 1950s. This area experienced three large (moment magnitudes >8) earthquakes in 1811 to 1812. The orientation and sense of shear is consistent with right-lateral strike slip motion along a northeast-trending fault zone (as indicated by current seismicity). Detection of crustal strain accumulation may be a useful discriminant for identifying areas where potentially damaging intraplate earthquakes may occur despite the absence of large earthquakes during historic time.     

Slow deformation and lower seismic hazard at the new madrid seismic zone

Global Positioning System (GPS) measurements across the New Madrid seismic zone (NMSZ) in the central United States show little, if any, motion. These data are consistent with platewide continuous GPS data away from the NMSZ, which show no motion within uncertainties. Both these data and the frequency-magnitude relation for seismicity imply that had the largest shocks in the series of earthquakes that occurred in 1811 and 1812 been magnitude 8, their recurrence interval should well exceed 2500 years, longer than has been assumed. Alternatively, the largest 1811 and 1812 earthquakes and those in the paleoseismic record may have been much smaller than typically assumed. Hence, the hazard posed by great earthquakes in the NMSZ appears to be overestimated.     

Reconciling short recurrence intervals with minor deformation in the new madrid seismic zone

At least three great earthquakes occurred in the New Madrid seismic zone in 1811 and 1812. Estimates of present-day strain rates suggest that such events may have a repeat time of 1000 years or less. Paleoseismological data also indicate that earthquakes large enough to cause soil liquefaction have occurred several times in the past 5000 years. However, pervasive crustal deformation expected from such a high frequency of large earthquakes is not observed. This suggests that the seismic zone is a young feature, possibly as young as several tens of thousands of years old and no more than a few million years old.     

Stream networks and long-term surface uplift in the new madrid seismic zone

Stream networks are sensitive to low rates of surface uplift and can be used to decipher the history of large earthquakes even where faults do not rupture the surface, as in intraplate seismic zones. Statistical analysis of alluvial network data from topographic maps in the New Madrid seismic zone, in the central United States, shows that stream-segment gradients deviate the most from an estimated natural stream profile where surface uplift is greatest. Evidence of cumulative deformation distilled from stream network patterns represents at least several meters of differential surface uplift during Holocene time, which suggests that more than one cycle of surface deformation occurred.     

A mechanical model for intraplate earthquakes: application to the new madrid seismic zone

We present a time-dependent model for the generation of repeated intraplate earthquakes that incorporates a weak lower crustal zone within an elastic lithosphere. Relaxation of this weak zone after tectonic perturbations transfers stress to the overlying crust, generating a sequence of earthquakes that continues until the zone fully relaxes. Simulations predict large (5 to 10 meters) slip events with recurrence intervals of 250 to 4000 years and cumulative offsets of about 100 meters, depending on material parameters and far-field stress magnitude. Most are consistent with earthquake magnitude, coseismic slip, recurrence intervals, cumulative offset, and surface deformation rates in the New Madrid Seismic Zone. Computed interseismic strain rates may not be detectable with available geodetic data, implying that low observed rates of strain accumulation cannot be used to rule out future damaging earthquakes.     

Double seismic zone for deep earthquakes in the izu-bonin subduction zone

A double seismic zone for deep earthquakes was found in the Izu-Bonin region. An analysis of SP-converted phases confirms that the deep seismic zone consists of two layers separated by approximately 20 kilometers. Numerical modeling of the thermal structure implies that the hypocenters are located along isotherms of 500 degrees to 550 degrees C, which is consistent with the hypothesis that deep earthquakes result from the phase transition of metastable olivine to a high-pressure phase in the subducting slab.     

Dislocation damping and anisotropic seismic wave attenuation in Earth's upper mantle

Crystal defects form during tectonic deformation and are reactivated by the shear stress associated with passing seismic waves. Although these defects, known as dislocations, potentially contribute to the attenuation of seismic waves in Earth's upper mantle, evidence for dislocation damping from laboratory studies has been circumstantial. We experimentally determined the shear modulus and associated strain-energy dissipation in pre-deformed synthetic olivine aggregates under high pressures and temperatures. Enhanced high-temperature background dissipation occurred in specimens pre-deformed by dislocation creep in either compression or torsion, the enhancement being greater for prior deformation in torsion. These observations suggest the possibility of anisotropic attenuation in relatively coarse-grained rocks where olivine is or was deformed at relatively high stress by dislocation creep in Earth's upper mantle.     

A seismotectonic model for the 300-kilometer-long eastern tennessee seismic zone

Ten years of monitoring microearthquakes with a regional seismic network has revealed the presence of a well-defined, linear zone of seismic activity in eastern Tennessee. This zone produced the second highest release of seismic strain energy in the United States east of the Rocky Mountains during the last decade, when normalized by crustal area. The data indicate that seismicity produced by regional, intraplate stresses is now concentrating near the boundary between relatively strong and weak basement crustal blocks.     

Fault zone connectivity: slip rates on faults in the san francisco bay area, california

The slip rate of a fault segment is related to the length of the fault zone of which it is part. In turn, the slip rate of a fault zone is related to its connectivity with adjoining or contiguous fault zones. The observed variation in slip rate on fault segments in the San Francisco Bay area in California is consistent with connectivity between the Hayward, Calaveras, and San Andreas fault zones. Slip rates on the southern Hayward fault taper northward from a maximum of more than 10 millimeters per year and are sensitive to the active length of the Maacama fault.     

An inverted double seismic zone in chile: evidence of phase transformation in the subducted slab

Data from two microseismic field experiments in northern Chile revealed an elongated cluster of earthquakes in the subducted Nazca plate at a depth of about 100 kilometers in which down-dip tensional events were consistently shallower than a family of compressional earthquakes. This double seismic zone shows a distribution of stresses of opposite polarity relative to that observed in other double seismic zones in the world. The distribution of stresses in northern Chile supports the notion that at depths of between 90 to 150 kilometers, the basalt to eclogite transformation of the subducting oceanic crust induces tensional deformation in the upper part of the subducted slab and compressional deformation in the underlying mantle.     

Earthquakes, faults, and nuclear power plants in southern new york and northern new jersey

Seismic activity in the greater New York City area is concentrated along several northeast-trending faults of which the Ramapo fault appears to be the most active. Three nuclear power plants at Indian Point, New York, are situated close to the Ramapo fault. For a reactor site in use for 40 years, the probability that the site will experience an intensity equal to or in excess of the design (safe shutdown) earthquake is estimated to be about 5 to 11 percent.     

Variation of interplate fault zone properties with depth in the japan subduction zone

The depth dependence of physical properties along the Japan subduction zone interface was explored using teleseismic recordings of earthquake signals. Broadband body waves were inverted to determine the duration of rupture and source depth for 40 interplate thrust earthquakes located offshore of Honshu between 1989 and 1995. After scaling for differences in seismic moment, there is a systematic decrease in rupture duration with increasing depth along the subducting plate interface. This indicates increases in rupture velocity or stress drop with depth, likely related to variation in rigidity of sediments on the megathrust.     

Deep crustal drilling in the north atlantic ocean

Oceanic crustal drilling by R. V. Glomar Challenger at 15 sites in the North Atlantic has led to a complex picture of the upper half kilometer of the crust. Elements of the picture include the absence of the source for linear magnetic anomalies, marked episodicity of volcanic activity, ubiquitous low temperature alteration and evidence for large scale tectonic disturbance. Comparison sections in the Pacific and much deeper crustal drilling are needed to attack problems arising from the North Atlantic results.     

Methionine adenosyltransferase deficiency: new enzymatic defect associated with hypermethioninemia

A specific deficiency of methionine adenosyltransferase has been demonstrated in the liver of an infant with hypermethioninemia. Since the enzymatic activity was below that in fetal liver and the metabolic abnormality has persisted (the infant now being 1 year of age), there is probably a genetic mutation. Mass screening for hypermethioninemia may uncover more such cases.     

Devonian brachiopods from the sillimanite zone, mount moosilauke, new hampshire

Devonian brachiopods, identifiable at the generic level, have been recovered from calc-silicate rocks more intensely metamorphosed and metasomatized than any other known fossil occurrence. The fossils are a key stratigraphic link between granulite facies rocks of central New Hampshire and fossiliferous rocks of western New Hampshire and Maine.     

Deep seismic sounding with nuclear explosives in the soviet union

A large geophysical program of exploration that uses deep seismic sounding has been under way in the Soviet Union for decades. Underground nuclear explosives have been used as strong seismic sources since 1971. The wide spacing between these seismic sources-for example, 500 kilometers-has permitted seismic exploration of inaccessible areas in traverses up to 3000 kilometers in length. During the same time an ultra-deep drilling program has also been under way. The data gathered have been used to elucidate details of the crust as well as to describe layering and inhomogeneities in the underlying mantle. By Soviet account, deep seismic sounding has been instrumental in confirming the existence of numerous sedimentary structures containing oil and gas fields in western and eastern Siberia.     

Diversity in metagenomic sequences reveals new pathogenic fungus associated with smut in Job's tears

Smut is a serious disease in Job's tears, also known as adlay, and contributes to the reduction of crop yield in agricultural fields. In this study, the key pathogenic fungi in adlay smut disease were first identified by internal transcribed spacer region(ITS) high-throughput sequencing and then used to elucidate the composition and diversity of the fungal community in adlay smut. Results indicate that an abundance of operational taxonomic units(OTUs) were detected in the infected involucres of flowering plants and the OTUs were classified to nine phyla, 20 classes, 45 orders, 90 families and 119 genera. A total of 4 986 OTUs clustered together, sharing six core OTUs in all samples, while 145 OTUs were shared among four geographical groups. The Shannon and Simpson indices ranged from 0.137–1.629 and 0.357–0.970, respectively. Community diversity ranked as Anshun(AS)Qinglong(QL)Xingren(XR)Xingyi(XY) among the four geographical groups by Shannon and Simpson indices, exhibiting complex community diversities among accessions and geographical groups. The richness and diversity data imply a weak relationship between the accession community richness and geographical origins of samples. Two closely related fungal genera, Sporisorium and Ustilago, were implicated as causes of smut disease. The genus Sporisorium appears to be more commonly found among accessions and thus is more likely to be the fungal pathogen causing smut in adlay. This work can facilitate strategies to control and prevent smut infection to improve adlay yield.     

沈阳新城区土地利用结构及生态足迹分析

依据用地面积分布数据和开发建设规划,利用信息熵和土地利用均衡度指标,分析了沈北新区土地利用结构的变化趋势.结果表明:沈北新区土地利用信息熵和均匀度总体呈下降趋势,土地利用系统向相对有序状态发展,土地利用的均质性减小,土地利用方式趋向多样化;研究区人均生态足迹为1.22 hm2/人,生态赤字达0.93 hm2/人,处于不可持续发展状态.