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1.
Stochastic finite-fault modeling is an important tool for simulating moderate to large earthquakes. It has proven to be useful in applications that require a reliable estimation of ground motions, mostly in the spectral frequency range of 1 to 10 Hz, which is the range of most interest to engineers. However, since there can be little resemblance between the low-frequency spectra of large and small earthquakes, this portion can be difficult to simulate using stochastic finite-fault techniques. This paper introduces two different methods to scale low-frequency spectra for stochastic finite-fault modeling. One method multiplies the subfault source spectrum by an empirical function. This function has three parameters to scale the low-frequency spectra: the level of scaling and the start and end frequencies of the taper. This empirical function adjusts the earthquake spectra only between the desired frequencies, conserving seismic moment in the simulated spectra. The other method is an empirical low-frequency coefficient that is added to the subfault corner frequency. This new parameter changes the ratio between high and low frequencies. For each simulation, the entire earthquake spectra is adjusted, which may result in the seismic moment not being conserved for a simulated earthquake. These low-frequency scaling methods were used to reproduce recorded earthquake spectra from several earthquakes recorded in the Pacific Earthquake Engineering Research Center (PEER) Next Generation Attenuation Models (NGA) database. There were two methods of determining the stochastic parameters of best fit for each earthquake: a general residual analysis and an earthquake-specific residual analysis. Both methods resulted in comparable values for stress drop and the low-frequency scaling parameters; however, the earthquake-specific residual analysis obtained a more accurate distribution of the averaged residuals. 相似文献
2.
The aim of this paper is to understand the seismic anisotropy of the overburden shale in an oilfield in the North West Shelf of Western Australia. To this end, we first find the orientation of the symmetry axis of a spherical shale sample from measurements of ultrasonic P‐wave velocities in 132 directions at the reservoir pressure. After transforming the data to the symmetry axis coordinates, we find Thomsen's anisotropy parameters δ and ? using these measurements and measurements of the shear‐wave velocity along the symmetry axis from a well log. To find these anisotropy parameters, we use a very fast simulated re‐annealing algorithm with an objective function that contains only the measured ray velocities, their numerical derivatives and the unknown elasticity parameters. The results show strong elliptical anisotropy in the overburden shale. This approach produces smaller uncertainty of Thomsen parameter δ than more direct approaches. 相似文献
3.
Depth determination of small shallow earthquakes in eastern Canada from maximum power Rg/Sg spectral ratio 总被引:1,自引:0,他引:1
For small earthquakes, focal depths can be estimated jointly when epicenters are located using the arrival times of Pg and Sg waves recorded at seismic stations close to the event. However, if regional network coverage is sparse, this approach does
not give accurate results. An alternative solution is the use of the regional depth-phase modeling (RDPM) method when such
depth phases are available. Small, shallow earthquakes can generate Rg waves, the amplitudes of which approximately attenuate exponentially with focal depth; whereas, the amplitudes of Sg waves are, on average, less dependent on focal depth. Based on these features, a method using the maximum power spectral
ratio (MPSR) between the Rg and Sg segments was developed to determine focal depth. Tests show the focal depth solutions obtained by the MPSR and RDPM methods
for five events in an earthquake swarm and one event acquired by inspection are in good agreement. The error in the MPSR-determined
focal depth caused by the error in the epicentral distance is in the order of 0.1 km. The error in the focal depth when using
a default focal mechanism is in the order of 0.5 km. The quality factor, Q does not generate a significant error. Using the average of focal depths can provide a more reliable solution. Using an azimuth
of approximately 45° from the strike direction to generate the synthetic ratio curve can reduce the error. As with any other
earthquake locating technique, a reasonable regional crustal model is required when the MPSR method is used. Case studies
show that the MPSR method can be used to successfully determine focal depths for events as small as m
N 1.6. 相似文献
4.
The basic parameters for the earthquake with a moment magnitude (M W) of 5.2 on the 23rd of June 2010 have been investigated. The earthquake occurred on a hidden fault in the northwest direction about 60?km north-northeast of Ottawa in the Western Quebec Seismic Zone (WQSZ) and had a focal depth of about 21?km. The focal mechanism was a thrust type with strike in the northwest direction and dipping in the northeast direction. The relative relocations of seven larger aftershocks show that the source rupture area was about 6?km2. The b value of the aftershock sequence was 0.8?C1.0, and the decay rate of the aftershocks was faster than normal cases. The dominant seismogenic depths are about 12 to 22?km in most parts of the WQSZ, while the seismogenic depth along the Ottawa?CBonnechere Graben can be as deep as 28?km. Based on the seismic activity in the WQSZ and vicinity since 1961, it seems that the periods of moderate earthquakes are about 6?C10?years. 相似文献
5.
Dena Aufseeser 《Urban geography》2013,34(6):870-888
In this article, I develop a critical analysis of the relationship between urban “revitalization” campaigns and the regulation of street children in Lima, Peru. Scholars writing mostly in the Global North have drawn attention to increasingly punitive policies regarding public space. While in many regards Lima’s urban policy is reflective of such larger trends, I consider whether the regulation of street children is as punitive as might be assumed. I am particularly concerned with the role that children’s rights play as another logic structuring urban regulation. I first show how a language of children’s rights has been manipulated to justify the removal of street children from public space, as is most evident through Peru’s Law to Protect Minors from Situations of Begging. However, there is also something more ambiguous occurring. In the second part of this article, I examine the uneven implementation of policy: street children themselves resist and rework policies “on the ground,” and children’s rights frameworks may offer possibilities for rupture of formal regulation. I suggest that these overlapping and competing dynamics sustain an uneven and contingent geography of urban regulation. 相似文献
6.
Richard D. Brodeur Dena M. Gadomski William G. Pearcy Harold P. Batchelder Charles B. Miller 《Estuarine, Coastal and Shelf Science》1985,21(3):365-378
The abundance and distribution patterns of nearshore ichthyoplankton were investigated during a year of anomalously high sea temperatures off Oregon. Samples collected from 2 to 18 km offshore from April through September of 1983 showed increased occurrences and higher abundances of taxa usually found at distances offshore of 37 km in other years. The dominant species collected, comprising more than half of the total larval fish abundance, was the northern anchovy (Engraulis mordax). Larval anchovy have rarely been collected inshore in previous studies. Many of the dominant taxa normally found inshore, especially osmerids, were present in reduced numbers in 1983. Changes in the hydrographic conditions associated with onshore surface drift and reduced summer upwelling during the 1983 El Niño could explain the distributional patterns observed. The warm inshore waters apparently provided a substantial spatial and temporal expansion of the spawning habitat for E. mordax. 相似文献
7.
Photometric observations of GO Cyg were performed during July–October 2002, in B and V filters (Johnson system). Using the
Wilson's computer codes, the light curve analysis were carried out to find the photometric elements of the system. The O-C
diagram which is based on the observed times of minima as well as those found in the literature, suggests a negative rate
of period variation (i.e. ) for the system. 相似文献
8.
Photometric observations of the eccentric eclipsing binary V1143 Cyg were performed during Aug.–Sep. 2000 and July 2002, in
Johnson B and V bands. The analysis of both light curves was made separately using the 1998 version of Wilson’s LC code. In order to find
a new observed rate of apsidal motion, we followed the procedure described by Guinan and Maloney (1985). A new observed rate
of apsidal motion of 3∘.72/100 yr was computed, which is close to the one reported earlier by Khaliullin (1983), Gimenez and Margrave (1985), and
Burns et al. (1996). 相似文献
9.
Many crucial tasks in seismology, such as locating seismic events and estimating focal mechanisms, need crustal velocity models. The velocity models of shallow structures are particularly important in the simulation of ground motions. In southern Ontario, Canada, many small shallow earthquakes occur, generating high-frequency Rayleigh (Rg) waves that are sensitive to shallow structures. In this research, the dispersion of Rg waves was used to obtain shear-wave velocities in the top few kilometers of the crust in the Georgian Bay, Sudbury, and Thunder Bay areas of southern Ontario. Several shallow velocity models were obtained based on the dispersion of recorded Rg waves. The Rg waves generated by an m N 3.0 natural earthquake on the northern shore of Georgian Bay were used to obtain velocity models for the area of an earthquake swarm in 2007. The Rg waves generated by a mining induced event in the Sudbury area in 2005 were used to retrieve velocity models between Georgian Bay and the Ottawa River. The Rg waves generated by the largest event in a natural earthquake swarm near Thunder Bay in 2008 were used to obtain a velocity model in that swarm area. The basic feature of all the investigated models is that there is a top low-velocity layer with a thickness of about 0.5 km. The seismic velocities changed mainly within the top 2 km, where small earthquakes often occur. 相似文献
10.