Correlations in aftershock and seismicity patterns     

Robert Shcherbakov  Jordan Van Aalsburg  John B. Rundle  Donald L. Turcotte   《Tectonophysics》2006,413(1-2):53

Correlations in space and time play a fundamental role in earthquake processes. One direct manifestation of the effects of correlations is the occurrence of aftershocks due to the stress transfer in the vicinity of a main shock. Less obvious and more speculative changes in correlations may occur in the background seismicity before large earthquakes. Using statistical physics it is possible to introduce a measure of spatial correlations through a correlation length. This quantity characterizes how local fluctuations can influence the occurrence of earthquakes over distances comparable with the correlation length. In this work, the physical basis of spatial correlations of earthquakes is discussed in the context of critical phenomena and the percolation problem. The method of two-point correlation function is applied to the seismicity of California. Well defined variations in time of the correlation length are found for aftershock sequences and background seismicity. The scaling properties of our obtained distributions are analyzed with respect to changes in several scaling parameters such as lower magnitude cutoff of earthquakes, the maximum time interval between earthquakes, and the spatial size of the area considered. This scaling behavior can be described in a unified manner by utilizing the multifractal fit. Utilizing the percolation approach the time evolution of clusters of earthquakes is studied with the correlation length defined in terms of the radius of gyration of clusters. This method is applied to the seismicity of California.  相似文献   

An inverse cascade model for self-organized complexity and natural hazards     

Gleb Yakovlev  William I. Newman  Donald L. Turcotte  Andrei Gabrielov 《Geophysical Journal International》2005,163(2):433-442

  相似文献   

The mid-ocean ridge axial valley as a steady-state neck     

Steven H. Emerman  D.L. Turcotte 《Earth and Planetary Science Letters》1984,71(1):141-146

In this paper the mid-ocean ridge axial valley is modelled as a steady-state lithospheric neck in which lithospheric stretching balances lithospheric accretion. Conversely, the axial high is a steady-state lithospheric bulge. The lithosphere is modelled as a thin plate with a Newtonian rheology. It is shown that an axial valley will occur if the rate of viscosity increase away from the ridge axis is faster than the rate at which accretion decreases. An axial high will occur if the opposite condition holds. This is consistent with the observation that axial valleys occur at low spreading rates and axial highs at high spreading rates. By fitting our model to profiles across the Mid-Atlantic Ridge and the East Pacific Rise and assuming the lithospheric thickness at the ridge axis to be 5 km, we find accretion widths of 6–8 km. We find the width over which there is a significant increase in lithospheric viscosity to be also 6–8 km.  相似文献   

Synthetic coral-reef terraces and variations of Quaternary sea level     

D.L. Turcotte  M.J. Bernthal 《Earth and Planetary Science Letters》1984,70(1):121-128

Coral-reef terraces on tectonically elevated coasts provide important data on variations of sea level. In this paper a systematic approach is presented for the construction of synthetic reef terraces. Idealized reef terraces are generated assuming a constant rate of tectonic uplift ν and a harmonic variation of sea level with amplitudeh_wo and period τ. It is further assumed that coral terraces grow only during periods of relative sea-level rise. The behavior is governed by the parameter u = τυ/2π h_wo. If u > 1 no reef terraces form. If 0.217 < u < 1 a discontinuous series of terraces form on the uplifting basement. If 0 < u < 0.217 the basement is covered with coral and a series of coral terraces forms on this coral. Uplifted coral-reef terraces on the Huon Peninsula, Papua New Guinea, compare reasonably well with terraces generated by our model with τ = 20,000 years andh_wo = 21.4 m. We also compare the observed terraces with model terraces using the paleo sea level inferred from¹⁸O/¹⁶O data. The observed terraces are qualitatively similar to those predicted using the oxygen isotope data, however, the model terraces require larger relative sea-level variations with a near 20,000 year period than those inferred directly from the¹⁸O/¹⁶O data.  相似文献   

Along-strike magma mixing beneath mid-ocean ridges: effects on isotopic ratios     

P.M. Kenyon  D.L. Turcotte 《Earth and Planetary Science Letters》1987,84(4)

The effects of mixing processes on the isotopic variability of mid-ocean ridge basalts are studied. The processes considered are porous flow dispersion and convective mixing in magma chambers. Porous flow dispersion is capable of mixing magmas over distances of only a few tens of meters. Convective mixing, on the other hand, is found to produce mixing over scales of kilometers to hundreds of kilometers. Calculations of convective mixing are carried out for continuous magma chambers, where mixing is limited by convective processes, and for discontinuous chambers, where mixing is limited by chamber size. Preliminary comparison of our calculations with observations along the mid-ocean ridges shows that the calculations are consistent with the existence of a correlation between bathymetry and isotopic ratio at long, but not at short, wavelengths. They are also capable of explaining a decrease in isotopic variability with increasing spreading rate.  相似文献   

Chaotic seismic faulting with a mass-spring model and velocity-weakening friction     

Jie Huang  D. L. Turcotte 《Pure and Applied Geophysics》1992,138(4):569-589

We present a systematic analysis of the dynamical behavior introduced by fault zone heterogeneities, using a simple mass-spring model with velocity-weakening friction. The model consists of two sliding blocks coupled to each other and to a constant velocity driver by clastic springs. The state of this system can be characterized by the positions of the two blocks relative to the driver. Symmetry stabilizes the system and generates only cyclic behavior. For an asymmetric system where the frictional forces for the two blocks are not equal, the solutions exhibit chaotic behavior. The transition from stable cyclic behavior to chaos is characterized by the period-doubling route to chaos. Lyapunov exponents are computed to quantify the deterministic chaos and to locate the onset of the chaotic evolution in parameter space. In many examples of deterministic chaos, chaotic behavior of a low-order system implies chaos in similar higher order systems. Thus, our results provide substantial evidence that crustal deformation is an example of deterministic chaos.  相似文献   

A cellular-automata, slider-block model for earthquakes II. Demonstration of self-organized criticality for a 2-D system     

Jie Huang  Galina Narkounskaia  Donald L. Turcotte 《Geophysical Journal International》1992,111(2):259-269

  相似文献   

Can Damage Mechanics Explain Temporal Scaling Laws in Brittle Fracture and Seismicity?     

Donald L. Turcotte  Robert Shcherbakov 《Pure and Applied Geophysics》2006,163(5-6):1031-1045

Time delays associated with processes leading to a failure or stress relaxation in materials and earthquakes are studied in terms of continuum damage mechanics. Damage mechanics is a quasi-empirical approach that describes inelastic irreversible phenomena in the deformation of solids. When a rock sample is loaded, there is generally a time delay before the rock fails. This period is characterized by the occurrence and coalescence of microcracks which radiate acoustic signals of broad amplitudes. These acoustic emission events have been shown to exhibit power-law scaling as they increase in intensity prior to a rupture. In case of seismogenic processes in the Earth's brittle crust, all earthquakes are followed by an aftershock sequence. A universal feature of aftershocks is that their rate decays in time according to the modified Omori's law, a power-law decay. In this paper a model of continuum damage mechanics in which damage (microcracking) starts to develop when the applied stress exceeds a prescribed yield stress (a material parameter) is introduced to explain both laboratory experiments and systematic temporal variations in seismicity.  相似文献   

Magma migration beneath an ocean ridge     

J.L. Ahern  D.L. Turcotte 《Earth and Planetary Science Letters》1979,45(1):115-122

Basaltic volcanism which forms the oceanic crust at mid-ocean ridges is the result of pressure release melting associated with ascending mantle convection. We present a model that gives the distribution of melting beneath the ridge and the subsequent migration of magma through the asthenosphere. In order to produce the degree of partial melting associated with the basaltic rocks making up the ocean crust, melting must extend to a depth of at least 70 km. Small degrees of partial melting are expected to result in an interconnected permeability along grain intersections. Due to the differential buoyancy of the magma relative to the residual solid the magma will be rapidly driven upwards. Solid-state creep allows the solid matrix to collapse as the magma migrates upwards and the lithostatic pressure in the matrix is nearly equal to the fluid pressure in the magma. The percentage partial melt present is only slightly greater than that necessary for the development of interconnected permeability and is much less than the degree of partial melting. The first partial melt fraction produced at the greatest depths migrates upwards and mixes with the later partial melt fractions produced at shallower depths. The uniformity of this mixing will have a profound effect on the chemistry of the basalts of the oceanic crust.  相似文献   

An elastic-perfectly plastic analysis of the bending of the lithosphere at a trench   总被引：1，自引：0，他引：1  

D.L. Turcotte  D.C. McAdoo  J.G. Caldwell 《Tectonophysics》1978,47(3-4)

A number of authors have modelled the flexure of the lithosphere at an oceanic trench using a thin elastic plate with a hydrostatic restoring force. In some cases good agreement with observed topography is obtained but in other cases the slope of the lithosphere within the trench is greater than that predicted by the elastic theory. In this paper the bending of a thin plate is considered using an elastic-perfectly plastic rheology. It is found that the lithosphere behaves elastically seaward of the trench, but that plasticity decreases the radius of curvature within the trench. The results are compared with a number of observed trench profiles. The elastic-perfectly plastic profiles are in excellent agreement with those profiles that deviate from elastic behavior.  相似文献