Chemical and Physical Characteristics of Pulverized Tejon Lookout Granite Adjacent to the San Andreas and Garlock Faults: Implications for Earthquake Physics

We present new detailed analyses of samples of pulverized Tejon Lookout granite collected from sections adjacent to the San Andreas and Garlock faults in southern California. The Tejon Lookout granite is pulverized in all exposures within about 100 m from both faults. Chemical analyses indicate no or little weathering in the collected samples, although XRD analysis shows the presence of smectite, illite, and minor kaolinite in the clay-size fraction. Weathering products may dominate in the less than 1 micron fraction. The average grain size in all samples of pulverized Tejon Lookout granite ranges between 26 and 208 microns (silt to fine sand), with the particle size distribution in part a function of proximity to the primary slip zone. The San Andreas fault samples that we studied are generally finer grained than those collected from adjacent to the Garlock fault. The particle size distribution for each studied sample from both faults follows a pseudo-power law with a continuously changing exponent, which suggests that pulverization is not simply a consequence of direct shear. The average particle size that we determined for our samples is considerably coarser than reported in previous investigations, which we attribute to possible measurement errors in the prior work. Our data and observations suggest that dynamic fracturing in the wall rock of the San Andreas and Garlock faults only accounts for about 1% or less of the earthquake energy budget.     

Scaling relations of earthquakes and aseismic deformation in a damage rheology model

We perform analytical and numerical studies of scaling relations of earthquakes and partition of elastic strain energy between seismic and aseismic components using a thermodynamically based continuum damage model. Brittle instabilities occur in the model at critical damage level associated with loss of convexity of the strain energy function. A new procedure is developed for calculating stress drop and plastic strain in regions sustaining brittle instabilities. The formulation connects the damage rheology parameters with dynamic friction of simpler frameworks, and the plastic strain accumulation is governed by a procedure that is equivalent to Drucker–Prager plasticity. The numerical simulations use variable boundary forces proportional to the slip-deficit between the assumed far field plate motion and displacement of the boundary nodes. These boundary conditions account for the evolution of elastic properties and plastic strain in the model region. 3-D simulations of earthquakes in a model with a large strike-slip fault produce scaling relations between the scalar seismic potency, rupture area, and stress drop values that are in good agreement with observations and other theoretical studies. The area and potency of the simulated earthquakes generally follow a linear log–log relation with a slope of 2/3, and are associated with stress drop values between 1 and 10 MPa. A parameter-space study shows that the area-potency scaling is shifted to higher stress drops in simulations with parameters corresponding to lower dynamic friction, more efficient healing, and higher degree of seismic coupling.     

RATIONALIZATION AND DECONCENTRATION OF THE U.S. CONTAINER PORT SYSTEM

The recent development of intermodal transportation and the relaxation of U.S. transport regulations have encouraged ocean carriers to rationalize their port schedules. Container shipping is therefore believed to concentrate shipping at a few large ports. Port traffic analysis, using the Lorenz Curve and Gini Coefficient, reveals, nevertheless, that the structure of the U.S. port system is actually becoming less concentrated. The challenge of secondary ports and changes in the transportation system explain this deconcentration.     

Earthquake activity related to seismic cycles in a model for a heterogeneous strike-slip fault

We investigate the evolution of seismicity within large earthquake cycles in a model of a discrete strike-slip fault in elastic solid. The model dynamics is governed by realistic boundary conditions consisting of constant velocity motion of regions around the fault, static/kinetic friction and dislocation creep along the fault, and 3D elastic stress transfer. The fault consists of brittle parts which fail during earthquakes and undergo small creep deformation between events, and aseismic creep cells which are characterized by high ongoing creep motion. This mixture of brittle and creep cells is found to generate realistic aftershock sequences which follow the modified Omori law and scale with the mainshock size. Furthermore, we find that the distribution of interevent times of the simulated earthquakes is in good agreement with observations. The temporal occurrence, however, is magnitude-dependent; in particular, the small events are clustered in time, whereas the largest earthquakes occur quasiperiodically. Averaging the seismicity before several large earthquakes, we observe an increase of activity and a broadening scaling range of magnitudes when the time of the next mainshock is approached. These results are characteristics of a critical point behavior. The presence of critical point dynamics is further supported by the evolution of the stress field in the model, which is compatible with the observation of accelerating moment release in natural fault systems.     

Biogene,klastische und evaporitische Sedimentation in einem mesothermen monomiktischen ufernahen See (Golf von Aqaba)

The genesis and development of a monomictic, mesothermal lake and its sediments is demonstrated by the analysis of sediment cores from different parts of the lake and from different stages of development. The compounds which build up the sediments, consist of irregular large particles from the surrounding crystalline rocks, of fine grained silt sediments from catastrophic flud deposits, of evaporitic series, and algae mats. The thickness of the different layers and their distribution in various parts of the lake; the different compounds, absolute age determinations, the carbonate layers and algae mats allow the definition of different stages of development of the lake. Causes and influences of an unusual type of monomixis with summer turnover are discussed and related to the sedimentary environment. Annual fluctuations in physical and biological limnology lead to the development of annual cycles in mat development and evaporites, which are reflected in the varved sediments. Inorganic sedimentation of terrestrial sediments, evaporites and organic matter accumulation are in shifting equilibrium which can be analysed by changes in the sediment types. Within the zone of biologic decay of algae via photosynthetic and other sulfur bacteria and heterotrophic bacteria, biogenic aragonite, Mg-Calcite and sulfides are precipitated. The autigenic dolomite occuring within the algae mats could not be attributed to biological precipitation so far. The lake started out as a lagoon approximately 4500 years B.P. Algae mat development was initiated after the lagoon was separated from the open sea (2400 B.P.). The central parts of the lake subsided at a time between 1900 and 1600 B.P. At this time the algae mat deposition, which until then took place in the whole lake, was restricted to the remaining shallow parts. Years of extremely high precipitation and catastrophic floods are represented by silt layers in the western parts of the lake, while coarser terrestrial sediments are intercalated in the algae mats of the eastern parts. Oöids, carbonate laminae, oncoliths and other types of carbonate particles within the algae mats are defined as biogenic by SEM analyses and laboratory experiments.