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91.
Discrimination of induced seismicity by full moment tensor inversion and decomposition 总被引:3,自引:1,他引:2
Human activities, including operations related to mining and reservoir exploitation, may induce seismicity and pose a risk for population and infrastructures. While different observations are commonly used to assess the origin of earthquakes, there is a lack of rules and methods for the discrimination between natural and induced seismicity. The inversion and decomposition of the full moment tensor and the observation of relevant deviation from a pure double couple (DC) model may be an indicator for induced seismicity. We establish here a common procedure to analyse a set of natural and induced events of similar magnitude, which occurred in Germany and neighbouring regions. The procedure is based on an inversion method and on a consistent velocity model and recording network. Induced seismicity is recorded during different mining and/or reservoir exploitations. Moment tensors are inverted using a multi-step inversion approach. This method, which was successfully applied in previous studies at regional and teleseismic distances, is further developed here to account for full moment tensor analysis. We first find a best DC solution and then perform a full moment tensor inversion, fitting full waveforms amplitude spectra at regional distances. The moment tensor solution is decomposed into DC, compensated linear vector dipole and isotropic terms. The discrimination problem is then investigated through the evaluation of distributions of non-DC source components for natural and induced data sets. Results illustrate the potential of the inversion and discrimination approach. Additional detailed analyses are carried out for the two most significant induced earthquakes, and rupture models are compared with the full moment tensor solutions. 相似文献
92.
A probabilistic approach for the classification of earthquakes as ��triggered�� or ��not triggered��
Luigi Passarelli Francesco Maccaferri Eleonora Rivalta Torsten Dahm Elias Abebe Boku 《Journal of Seismology》2013,17(1):165-187
The occurrence time of earthquakes can be anticipated or delayed by external phenomena that induce strain energy changes on the faults. ??Anticipated?? earthquakes are generally called ??triggered??; however, it can be controversial to label a specific earthquake as such, mostly because of the stochastic nature of earthquake occurrence and of the large uncertainties usually associated to stress modelling. Here we introduce a combined statistical and physical approach to quantify the probability that a given earthquake was triggered by a given stress-inducing phenomenon. As an example, we consider an earthquake that was likely triggered by a natural event: the M?=?6.2 13 Jan 1976 Kópasker earthquake on the Grímsey lineament (Tj?rnes Fracture Zone, Iceland), which occurred about 3?weeks after a large dike injection in the nearby Krafla fissure swarm. By using Coulomb stress calculations and the rate-and-state earthquake nucleation theory, we calculate the likelihood of the earthquake in a scenario that contains only the tectonic background and excludes the dike and in a scenario that includes the dike but excludes the background. Applying the Bayes?? theorem, we obtain that the probability that the earthquake was indeed triggered by the dike, rather than purely due to the accumulation of tectonic strain, is about 60 to 90?%. This methodology allows us to assign quantitative probabilities to different scenarios and can help in classifying earthquakes as triggered or not triggered by natural or human-induced changes of stress in the crust. 相似文献
93.
Imaging a shallow salt diapir using ambient seismic vibrations beneath the densely built-up city area of Hamburg,Northern Germany 总被引:1,自引:1,他引:0
Salt diapirs are common features of sedimentary basins. If close to the surface, they can bear a significant hazard due to
possible dissolution sinkholes, karst formation and collapse dolines or their influence on ground water chemistry. We investigate
the potential of ambient vibration techniques to map the 3-D roof morphology of shallow salt diapirs. Horizontal-to-vertical
(H/V) spectral peaks are derived at more than 900 positions above a shallow diapir beneath the city area of Hamburg, Germany,
and are used to infer the depth of the first strong impedance contrast. In addition, 15 small-scale array measurements are
conducted at different positions in order to compute frequency-dependent phase velocities of Rayleigh waves between 0.5 and
25 Hz. The dispersion curves are inverted together with the H/V peak frequency to obtain shear-wave velocity profiles. Additionally,
we compare the morphology derived from H/V and array measurements to borehole lithology and a gravity-based 3-D model of the
salt diapir. Both methods give consistent results in agreement with major features indicated by the independent data. An important
result is that H/V and array measurements are better suited to identify weathered gypsum caprocks or gypsum floaters, while
gravity-derived models better sample the interface between sediments and homogeneous salt. We further investigate qualitatively
the influence of the 3-D subsurface topography of the salt diapir on the validity of local 1-D inversion results from ambient
vibration dispersion curve inversion. 相似文献
94.
Improved estimates of mean sea level changes in the German Bight over the last 166 years 总被引:1,自引:1,他引:0
In this paper, mean sea level changes in the German Bight, the south-eastern part of the North Sea, are analysed. Records
from 13 tide gauges covering the entire German North Sea coastline and the period from 1843 to 2008 have been used to derive
high quality relative mean sea level time series. Changes in mean sea level are assessed using non-linear smoothing techniques
and linear trend estimations for different time spans. Time series from individual tide gauges are analysed and then ‘virtual
station’ time series are constructed (by combining the individual records) which are representative of the German Bight and
the southern and eastern regions of the Bight. An accelerated sea level rise is detected for a period at the end of the nineteenth
century and for another one covering the last decades. The results show that there are regional differences in sea level changes
along the coastline. Higher rates of relative sea level rise are detected for the eastern part of the German Bight in comparison
to the southern part. This is most likely due to different rates of vertical land movement. In addition, different temporal
behaviour of sea level change is found in the German Bight compared to wider regional and global changes, highlighting the
urgent need to derive reliable regional sea level projections for coastal planning strategies. 相似文献
95.
International climate negotiations that aim at reducing global greenhouse gas emissions are strongly influenced by a conflict between rich and poor countries and by a lack of consensus about the urgency of emission reduction measures. We have previously in an experimental game characterised the implied challenge of avoiding dangerous climate change as the “collective-risk social dilemma”. Here we introduce heterogeneous wealth and two time horizons into the collective-risk social dilemma game. We show that rich players are willing to substitute for missing contributions by the poor, provided the players collectively face intermediate climate targets that, if not reached, are potentially followed by simulated intermediate costly climate risks. However, despite some increase in the contributions of the rich against the final collective target, the final target is reached less often than the intermediate target. Our results provide experimental evidence that similar, intermediate time horizons between climate risks and climate change mitigation planning are a necessary, though not sufficient, component of successful climate negotiations. 相似文献
96.
Least-squares harmonic estimation of the tropopause parameters using GPS radio occultation measurements 总被引:1,自引:0,他引:1
Mohammad Ali Sharifi Ali Sam Khaniani Salim Masoumi Torsten Schmidt Jens Wickert 《Meteorology and Atmospheric Physics》2013,120(1-2):73-82
In order to investigate temporal variations of the tropopause parameters, Least-Squares Harmonic Estimation (LS-HE) is applied to the time series of the tropopause temperatures and heights derived from Global Positioning System Radio Occultation (GPS RO) atmospheric profiles of CHAMP, GRACE and COSMIC missions from January 2006 until May 2010 in different regions of Iran. By applying the univariate LS-HE to the completely unevenly spaced time series of the tropopause temperatures and heights, annual and diurnal components are detected together with their higher harmonics. The multivariate LS-HE estimates the main periodic signals, particularly diurnal and semidiurnal cycles, more clearly than the univariate LS-HE. Mixing in the values of the tropopause height and temperature is seen to occur in winter at lower latitudes (around 30°) as a result of subtropical jet, and in summer at higher latitudes (36°–42°) as an effect of subtropical high. A bimodal pattern is observed in the frequency histograms of the tropopause heights, in which the primary modes for the southern and northern parts of Iran correspond to subtropical and extratropical heights, respectively. 相似文献
97.
Christoph Mayr Andreas Lücke Nora I. Maidana Michael Wille Torsten Haberzettl Hugo Corbella Christian Ohlendorf Frank Schäbitz Michael Fey Stephanie Janssen Bernd Zolitschka 《Journal of Paleolimnology》2009,42(1):81-102
A combination of carbon-to-nitrogen ratios (TOC/TN), Rock Eval-analyses, and stable isotope values of bulk nitrogen (δ15N) and organic carbon (δ13Corg) was used to characterize bulk organic matter (OM) of a piston core from the Patagonian maar lake Laguna Potrok Aike (Argentina)
for the purpose of palaeoenvironmental reconstruction. Sedimentary data were compared with geochemical signatures of potential
OM sources from Laguna Potrok Aike and its catchment area to identify the sources of sedimentary OM. Correlation patterns
between isotopic data and TOC/TN ratios allowed differentiation of five distinct phases with different OM composition. Before
8470 calibrated 14C years before present (cal. yrs BP) and after 7400 cal. yrs BP, isotopic and organo-geochemical fingerprints indicate that
the sediments of Laguna Potrok Aike consist predominantly of soil and diatom OM with varying admixtures of cyanobacterial
and aquatic macrophyte OM. For a short phase of the early Holocene (ca. 8470–7400 cal. yrs BP), however, extremely high input
of soil OM is implied by isotopic fingerprints. Previous seismic and geochronological results indicate a severe lake-level
drop of 33 m below present-day shortly before 6590 cal. yrs BP. It is suggested that this lake level drop was accompanied
by increased erosion of shore banks and channel incision enhancing soil OM deposition in the lake basin. Thus, isotopic data
can be linked to hydrological variations at Laguna Potrok Aike and allow a more precise dating of this extremely low lake
level. An isotopic mixing model was used including four different sources (soil, cyanobacteria, diatom and aquatic macrophyte
OM) to model OM variations and the model results were compared with quantitative microfossil data. 相似文献
98.
Torsten Haberzettl Flavio S. Anselmetti Sabine W. Bowen Michael Fey Christoph Mayr Bernd Zolitschka Daniel Ariztegui Barbara Mauz Christian Ohlendorf Stephanie Kastner Andreas Lücke Frank Schäbitz Michael Wille 《Quaternary Science Reviews》2009,28(25-26):2927-2939
Paleoenvironmental records extending well into the last glacial period are scarce in the steppe regions of southern South America. Here, we present a continuous record for the past 55 ka from the maar lake Laguna Potrok Aike (51°58′ S, 70°23′ W, southern Patagonia, Argentina). Previous studies on a sedimentary core from a lake level terrace near the northern margin of the lake covered parts of Oxygen Isotope Stage (OIS) 3 (59–29 ka) whereas a second core from the centre of the basin comprised the last 16 ka. Tephrostratigraphical constraints and OSL ages from a third core located below the lake level terrace provide the crucial piece to close the gap between the previous coring sites. High-resolution XRF and magnetic susceptibility as well as grain size data indicate a positive hydrological balance alongside with relatively high aeolian activity during the glacial which is contemporaneous with increased dust fluxes in Antarctica. This is therefore the first evidence for contemporaneity of aeolian deposition in both the target area (Antarctica) and in the major source area of Patagonia. During the Holocene climatic conditions driving sediment deposition seem to have been more variable and less dominated by wind compared to glacial times. The identification of a minor lake level lowering at approximately 4 cal ka BP allows to refine earlier paleoenvironmental reconstructions for the Holocene. Within error margins the OSL ages are consistent with published radiocarbon-dated records offering hence a valuable tool for further studies of the sediments from Laguna Potrok Aike. The new chronology confirms the age of three tephra layers up to now only found in Laguna Potrok Aike sediments and ascribed to OIS 3. 相似文献
99.
Jean Vallance Lluís Fontboté Massimo Chiaradia Agnès Markowski Susanne Schmidt Torsten Vennemann 《Mineralium Deposita》2009,44(4):389-413
The Jurassic (approximately 145 Ma) Nambija oxidized gold skarns are hosted by the Triassic volcanosedimentary Piuntza unit
in the sub-Andean zone of southeastern Ecuador. The skarns consist dominantly of granditic garnet (Ad20–98) with subordinate pyroxene (Di46–92Hd17–42Jo0–19) and epidote and are spatially associated with porphyritic quartz-diorite to granodiorite intrusions. Endoskarn is developed
at the intrusion margins and grades inwards into a potassic alteration zone. Exoskarn has an outer K- and Na-enriched zone
in the volcanosedimentary unit. Gold mineralization is associated with the weakly developed retrograde alteration of the exoskarn
and occurs mainly in sulfide-poor vugs and milky quartz veins and veinlets in association with hematite. Fluid inclusion data
for the main part of the prograde stage indicate the coexistence of high-temperature (500°C to >600°C), high-salinity (up
to 65 wt.% eq. NaCl), and moderate- to low-salinity aqueous-carbonic fluids interpreted to have been trapped at pressures
around 100–120 MPa, corresponding to about 4-km depth. Lower-temperature (510–300°C) and moderate- to low-salinity (23–2 wt.%
eq. NaCl) aqueous fluids are recorded in garnet and epidote of the end of the prograde stage. The microthermometric data (Th
from 513°C to 318°C and salinity from 1.0 to 23 wt.% eq. NaCl) and δ18O values between 6.2‰ and 11.5‰ for gold-bearing milky quartz from the retrograde stage suggest that the ore-forming fluid
was dominantly magmatic. Pressures during the early retrograde stage were in the range of 50–100 MPa, in line with the evidence
for CO2 effervescence and probable local boiling. The dominance of magmatic low-saline to moderately saline oxidizing fluids during
the retrograde stage is consistent with the depth of the skarn system, which could have delayed the ingression of external
fluids until relatively low temperatures were reached. The resulting low water-to-rock ratios explain the weak retrograde
alteration and the compositional variability of chlorite, essentially controlled by host rock compositions. Gold was precipitated
at this stage as a result of cooling and pH increase related to CO2 effervescence, which both result in destabilization of gold-bearing chloride complexes. Significant ingression of external
fluids took place after gold deposition only, as recorded by δ18O values of 0.4‰ to 6.2‰ for fluids depositing quartz (below 350°C) in sulfide-rich barren veins. Low-temperature (<300°C)
meteoric fluids (δ18Owater between −10.0‰ and −2.0‰) are responsible for the precipitation of late comb quartz and calcite in cavities and veins and
indicate mixing with cooler fluids of higher salinities (about 100°C and 25 wt.% eq. NaCl). The latter are similar to low-temperature
fluids (202–74.5°C) with δ18O values of −0.5‰ to 3.1‰ and salinities in the range of 21.1 to 17.3 wt.% eq. CaCl2, trapped in calcite of late veins and interpreted as basinal brines. Nambija represents a deep equivalent of the oxidized
gold skarn class, the presence of CO2 in the fluids being partly a consequence of the relatively deep setting at about 4-km depth. As in other Au-bearing skarn
deposits, not only the prograde stage but also the gold-precipitating retrograde stage is dominated by fluids of magmatic
origin. 相似文献
100.
André Waelkens Matteo Maturi Torsten Enßlin 《Monthly notices of the Royal Astronomical Society》2008,383(4):1425-1430
We consider the role of the Galactic kinetic Sunyaev–Zeldovich (SZ) effect as a cosmic microwave background (CMB) polarization foreground. While the Galactic thermal SZ effect has previously been studied and discarded as a potential CMB foreground, we find that the kinetic SZ effect is dominant in the Galactic case. We analyse the detectability of the kinetic SZ effect by means of an optimally matched filter technique applied to a simulation of an ideal observation. We obtain no detection, getting a signal-to-noise ratio of 0.1, thereby demonstrating that the kinetic SZ effect can also safely be ignored as a CMB foreground. However, we provide maps of the expected signal for inclusion in future high-precision data processing. Furthermore, we rule out the significant contamination of the polarized CMB signal by second scattering of Galactic kinetic SZ photons, since we show that the scattering of the CMB quadrupole photons by Galactic electrons is a stronger effect than the SZ second scattering, and has already been shown to produce no significant polarized contamination. 相似文献