Variation of P-wave velocity before and after the Galway Lake earthquake (M_L = 5.2) and the Goat Mountain earthquakes (M_L = 4.7, 4.7), 1975, in the Mojave desert, California

Since June 1973, the California Institute of Technology Seismological Laboratory has been monitoring quarry blasts in southern California for the purpose of detecting possible velocity changes before earthquakes. On June 1, 1975, an M_L = 5.2 earthquake occurred near Galway Lake, about 60 km southeast of Barstow, California. On November 15, 1975, and December 14, 1975, M_L = 4.7 earthquakes occurred about 30 km southeast of Galway Lake near Goat Mountain. These three epicenters are close to Hector and Victorville quarries, which have been monitored by CIT. First-motion data, the distribution of aftershocks, and ground breakage associated with the Galway Lake earthquake indicate right-lateral strike slip on a fault striking N20°W, dipping 70°SW. First-motion data and the distribution of aftershocks for the first Goat Mountain earthquake indicate normal dip slip on a plane striking north-northeast, dipping about 60° to the west-northwest. Blasts at Hector and Victorville quarries were timed with an accuracy of ± 0.01 sec, and first arrivals at a number of stations of the USGS-CIT network can be read to an accuracy of ± 0.02 sec. The data are plotted in terms of residuals versus time at each station in such a fashion as to reflect trends in velocity. Origin times of all earthquakes ≳ 4.0 in our study area are plotted on these curves. The most important results of this study are observations that are “negative” in character. These observations are: (1) no changes greater than about 0.1 sec (or about 1 per cent in average velocity) are seen at any station during the 2-year period of this study, (2) given the flatness of the curves, it is difficult to draw correlations between any larger earthquakes and changes in velocity. In particular, no unique change is seen before the Galway Lake earthquake along two paths that cross the epicentral region of this earthquake at right angles to each other. The data are such that only an anomaly less than 2 months in duration could have escaped detection. Similarly, no unique change is seen before the Goat Mountain earthquakes along two subparallel paths through the epicentral area. Only an anomaly less than 1 month in duration could have escaped detection. One observation that is “positive” in character can be made from the curves; namely, slight but systematic changes in velocity can be seen. For Hector blasts, most stations show a systematic increase in velocity with time of as much as 0.8 per cent. For Victorville blasts, most stations show an opposite trend. The results of this study are somewhat disappointing from the point of view of the standard dilatancy model, which predicts a 10 to 20 per cent decrease in P velocity over an area of several source dimensions in diameter before an earthquake. Before the M_L = 5.2 Galway Lake earthquake, this decrease should occur over an area about 30 km in diameter over a period of 3 to 6 months. Before the Goat Mountain earthquake, this decrease should have occurred over an area about 20 km in diameter over a period of 2 to 4 months. Our data preclude the possibility of precursory changes this large before these earthquakes. It is still possible that dilatancy accompanied these earthquakes, but the effect must have been small. It is also possible that these earthquakes are not representative of other M_L = 4.7 to 5.2 earthquakes; however, at least two different types of faulting are represented, namely strike slip and normal faulting. The small systematic changes in velocity that are seen may have one of the following explanations: (1) there were systematic variations in local delays at the two quarries, or (2) there were regional changes in crustal velocity. The fact that shot points migrated in more or less systematic fashions in both Hector and Victorville quarries during the period of this study suggests that the first explanation may be correct. The second explanation is intriguing, but the opposite trends for the Hector and Victorville data are somewhat puzzling, unless adjacent regions, one surrounding Hector quarry and one surrounding Victorville quarry, are simultaneously undergoing opposite changes in velocity. This possibility is difficult to evaluate. One can observe, however, that during the 2-year period of this study, all larger earthquakes were concentrated in the region of the Hector quarry, and there was simultaneously an absence of larger earthquakes in the region of the Victorville quarry. Perhaps the occurrence of larger earthquakes is related to rising velocities near Hector, if they are indeed rising. Such a correlation is reasonable if the velocity increase is due to tectonic stress loading

INFLUENCING THE INDENTATION CURVES BY THE BLUNTNESS OF THE BERKOVICH INDENTER AT THE FEM MODELLING

The influence of the Berkovich indenter bluntness on the indentation curves at nanoindentation test of fused silica is determined by the FEM (finite element method) in this paper. The Berkovich indenter, which is mostly used for the nanoindentation test, was assumed for calculations. The indenter is always blunted in real tests. The bluntness of the indenter has an influence on the results of the nanoindentation test. The combination of the nanoindentation test and the FE modelling can be used for the calculation of the parameters of fused silica plasticity and estimation of the bluntness of the indenter. In this paper, the FEM was used for calculating of the indentation curves. Two cases of bluntness were assumed. The curves for ideally sharp or blunted indenter were determined. The results of these calculations showed that the indentation curves are dependent on the bluntness of the Berkovich indenter. The greatest relative influence of the nanoindentation curves by the bluntness is in the area of small values of the indenter displacement. The impact of assuming blunted indenter to calculated parameters of plasticity was assessed. It is often difficult to measure the bluntness of the indenter but it has an influence on the results of the nanoindentation test and should be included into calculations to make it more precise

Analiza i modeliranje dinamičkih svojstava interaktivnog pogonskog sustava

The recent drive systems are considered as interactive systems containing a range of subsystems with different physical nature. This contribution deals with the modelling of mechatronic drive systems using numerical package DYNAST. The theoretical general observations are demonstrated on particular experiments on real system.Moderni pogonski sustavi smatraju se interaktivnim sustavima koji sadržavaju podsustave različitih fizikalnih svojstava. Ovaj dokument prikazuje modeliranje mehatroničkog pogonskog sustava korištenjem numeričkog paketa DYNAST. Načelna teorijska razmatranja demonstrirana su pomoću konkretnih eksperimenata na realnom sustavu

A tribute to George Plafker

In a long and distinguished career, George Plafker has made fundamental advances in understanding of megathrust tectonics, tsunami generation, paleoseismology, crustal neotectonics, and Alaskan geology, all by means of geological field observations. George discovered that giant earthquakes result from tens of meters of seismic slip on subduction thrusts, and he did this before the theory of plate tectonics had become a paradigm. The discovery was founded on George's comprehensive mapping of land-level changes in the aftermath of the 1964 earthquake in Alaska, and on his similar mapping in the region of the 1960 earthquakes in Chile. The mapping showed paired, parallel belts of coseismic uplift largely offshore and coseismic subsidence mostly onshore -- a pattern now familiar as the initial condition assumed in computer simulations of subduction-zone tsunamis. George recognized, moreover, that splay faulting can play a major role in tsunami generation, and he also distinguished carefully between tectonic and landslide sources for the multiple tsunamis that accounted for nearly all the fatalities associated with the 1964 Alaska earthquake. George's classic monographs on the 1964 earthquake include findings about subduction-zone paleoseismology that he soon extended to include stratigraphic evidence for cyclic vertical deformation at the Copper River delta, as well as recurrent uplift evidenced by flights of marine terraces at Middleton Island. As a geologist of earthquakes, George also clarified the tectonics and hazards of crustal faulting in Alaska, California, and overseas. All the while, George was mapping bedrock geology in Alaska, where he contributed importantly to today's understanding of of how terranes were accreted and modified

Three-Dimensional Basin and Fault Structure From a Detailed Seismic Velocity Model of Coachella Valley, Southern California

The Coachella Valley in the northern Salton Trough is known to produce destructive earthquakes, making it a high seismic hazard area. Knowledge of the seismic velocity structure and geometry of the sedimentary basins and fault zones is required to improve earthquake hazard estimates in this region. We simultaneously inverted first P wave travel times from the Southern California Seismic Network (39,998 local earthquakes) and explosions (251 land/sea shots) from the 2011 Salton Seismic Imaging Project to obtain a 3‐D seismic velocity model. Earthquakes with focal depths ≤10 km were selected to focus on the upper crustal structure. Strong lateral velocity contrasts in the top ~3 km correlate well with the surface geology, including the low‐velocity (<5 km/s) sedimentary basin and the high‐velocity crystalline basement rocks outside the valley. Sediment thickness is ~4 km in the southeastern valley near the Salton Sea and decreases to <2 km at the northwestern end of the valley. Eastward thickening of sediments toward the San Andreas fault within the valley defines Coachella Valley basin asymmetry. In the Peninsular Ranges, zones of relatively high seismic velocities (~6.4 km/s) between 2‐ and 4‐km depth may be related to Late Cretaceous mylonite rocks or older inherited basement structures. Other high‐velocity domains exist in the model down to 9‐km depth and help define crustal heterogeneity. We identify a potential fault zone in Lost Horse Valley unassociated with mapped faults in Southern California from the combined interpretation of surface geology, seismicity, and lateral velocity changes in the model

Geophysical evidence for the evolution of the California Inner Continental Borderland as a metamorphic core complex

Author Posting. © American Geophysical Union, 2000. This article is posted here by permission of American Geophysical Union for personal use, not for redistribution. The definitive version was published in Journal of Geophysical Research: Solid Earth 105 (2000): 5835-5857, doi:10.1029/1999JB900318.We use new seismic and gravity data collected during the 1994 Los Angeles Region Seismic Experiment (LARSE) to discuss the origin of the California Inner Continental Borderland (ICB) as an extended terrain possibly in a metamorphic core complex mode. The data provide detailed crustal structure of the Borderland and its transition to mainland southern California. Using tomographic inversion as well as traditional forward ray tracing to model the wide-angle seismic data, we find little or no sediments, low (#6.6 km/s) P wave velocity extending down to the crust-mantle boundary, and a thin crust (19 to 23 km thick). Coincident multichannel seismic reflection data show a reflective lower crust under Catalina Ridge. Contrary to other parts of coastal California, we do not find evidence for an underplated fossil oceanic layer at the base of the crust. Coincident gravity data suggest an abrupt increase in crustal thickness under the shelf edge, which represents the transition to the western Transverse Ranges. On the shelf the Palos Verdes Fault merges downward into a landward dipping surface which separates “basement” from low-velocity sediments, but interpretation of this surface as a detachment fault is inconclusive. The seismic velocity structure is interpreted to represent Catalina Schist rocks extending from top to bottom of the crust. This interpretation is compatible with a model for the origin of the ICB as an autochthonous formerly hot highly extended region that was filled with the exhumed metamorphic rocks. The basin and ridge topography and the protracted volcanism probably represent continued extension as a wide rift until ;13 m.y. ago. Subduction of the young and hot Monterey and Arguello microplates under the Continental Borderland, followed by rotation and translation of the western Transverse Ranges, may have provided the necessary thermomechanical conditions for this extension and crustal inflow.The LARSE experiment was funded by NSF EAR-9416774, the U.S. Geological Survey’s Earthquake Hazards and Coastal and Marine Programs, and by the Southern California Earthquake Center (SCEC)

A comparison between the transpressional plate boundaries of South Island, New Zealand, and Southern California, USA: the Alpine and San Andreas fault systems

There are clear similarities in structure and tectonics between the Alpine Fault system (AF) of New Zealand’s South Island and the San Andreas Fault system (SAF) of southern California, USA. Both systems are transpressional, with similar right slip and convergence rates, similar onset ages (for the current traces), and similar total offsets. There are also notable differences, including the dips of the faults and their plate-tectonic histories. The crustal structure surrounding the AF and SAF was investigated with active and passive seismic sources along transects known as South Island Geophysical Transect (SIGHT) and Los Angeles Region Seismic Experiment (LARSE), respectively. Along the SIGHT transects, the AF appears to dip moderately southeastward (~50 deg.), toward the Pacific plate (PAC), but along the LARSE transects, the SAF dips vertically to steeply northeastward toward the North American plate (NAM). Away from the LARSE transects, the dip of the SAF changes significantly. In both locations, a midcrustal decollement is observed that connects the plate-boundary fault to thrust faults farther south in the PAC. This decollement allows upper crust to escape collision laterally and vertically, but forces the lower crust to form crustal roots, reaching maximum depths of 44 km (South Island) and 36 km (southern California). In both locations, upper-mantle bodies of high P velocity are observed extending from near the Moho to more than 200-km depth. These bodies appear to be confined to the PAC and to represent oblique downwelling of PAC mantle lithosphere along the plate boundaries

Analiza i modeliranje dinamičkih svojstava interaktivnog pogonskog sustava

The recent drive systems are considered as interactive systems containing a range of subsystems with different physical nature. This contribution deals with the modelling of mechatronic drive systems using numerical package DYNAST. The theoretical general observations are demonstrated on particular experiments on real system.Moderni pogonski sustavi smatraju se interaktivnim sustavima koji sadržavaju podsustave različitih fizikalnih svojstava. Ovaj dokument prikazuje modeliranje mehatroničkog pogonskog sustava korištenjem numeričkog paketa DYNAST. Načelna teorijska razmatranja demonstrirana su pomoću konkretnih eksperimenata na realnom sustavu

Seismic imaging of the metamorphism of young sediment into new crystalline crust in the actively rifting Imperial Valley, California

Plate-boundary rifting between transform faults is opening the Imperial Valley of southern California and the rift is rapidly filling with sediment from the Colorado River. Three 65–90 km long seismic refraction profiles across and along the valley, acquired as part of the 2011 Salton Seismic Imaging Project, were analyzed to constrain upper crustal structure and the transition from sediment to underlying crystalline rock. Both first arrival travel-time tomography and frequency-domain full-waveform inversion were applied to provide P-wave velocity models down to ∼7 km depth. The valley margins are fault-bounded, beyond which thinner sediment has been deposited on preexisting crystalline rocks. Within the central basin, seismic velocity increases continuously from ∼1.8 km/s sediment at the surface to >6 km/s crystalline rock with no sharp discontinuity. Borehole data show young sediment is progressively metamorphosed into crystalline rock. The seismic velocity gradient with depth decreases approximately at the 4 km/s contour, which coincides with changes in the porosity and density gradient in borehole core samples. This change occurs at ∼3 km depth in most of the valley, but at only ∼1.5 km depth in the Salton Sea geothermal field. We interpret progressive metamorphism caused by high heat flow to be creating new crystalline crust throughout the valley at a rate comparable to the ≥2 km/Myr sedimentation rate. The newly formed crystalline crust extends to at least 7–8 km depth, and it is shallower and faster where heat flow is higher. Most of the active seismicity occurs within this new crust