scholarly journals The foreshock activity of the 1971 San Fernando earthquake, California

1978 ◽  
Vol 68 (5) ◽  
pp. 1265-1279
Author(s):  
Mizuho Ishida ◽  
Hiroo Kanamori
Keyword(s):  
Small Area ◽  
Main Shock ◽  
Source Region ◽  
Structural Heterogeneity ◽  
Propagation Path ◽  
Wave Form ◽  
Epicentral Area ◽  
Complex Wave ◽  
Wave Forms ◽  
San Fernando

abstract All of the earthquakes which occurred in the epicentral area of the 1971 San Fernando earthquake during the period from 1960 to 1970 were relocated by using the master-event method. Five events from 1969 to 1970 are located within a small area around the main shock epicenter. This cluster of activity is clearly separated spatially from the activity in the surrounding area, so these five events are considered foreshocks. The wave forms of these foreshocks recorded at Pasadena are, without exception, very complex, yet they are remarkably similar from event to event. The events which occurred in the same area prior to 1969 have less complex wave forms with a greater variation among them. The complexity is most likely the effect of the propagation path. A well located aftershock which occurred in the immediate vicinity of the main shock of the San Fernando earthquake has a wave form similar to that of the foreshocks, which suggests that the foreshocks are also located very close to the main shock. This complexity is probably caused by a structural heterogeneity in the fault zone near the hypocenter. The seismic rays from the foreshocks in the inferred heterogeneous zone are interpreted as multiple-reflected near the source region which yielded the complex wave form. The mechanisms of the five foreshocks are similar to each other but different from either the main shock or the aftershocks, suggesting that the foreshocks originated from a small area of stress concentration where the stress field is locally distorted from the regional field. The number of small events with S-P times between 3.8 to 6 sec recorded at Mt. Wilson each month suggests only a slight increase in activity of small earthquakes near the epicentral area during the 2-month period immediately before the main shock. However, because of our inability to locate these events, the evidence is not definitive. Since the change in the wave forms is definite the present result suggests that detailed analyses of wave forms, spectra, and mechanism can provide a powerful diagnostic method for identifying a foreshock sequence.

Effect of Forcing Terms and General Characteristics of Torsional Vibrations of Marine Engine Systems with Variable Inertia

1974 ◽  
Vol 18 (02) ◽  
pp. 131-138
Author(s):  
W. D. Carnegie ◽  
M. S. Pasricha
Keyword(s):  
Equations Of Motion ◽  
Mean Value ◽  
Wave Form ◽  
Actual System ◽  
Computer Methods ◽  
Reciprocating Engine ◽  
Complex Wave ◽  
Wave Forms ◽  
Crankshaft Rotation ◽  
Engine Systems

The torsional vibration phenomenon in the running gear of reciprocating engine systems is usually dealt with by considering a series of constant inertias connected by sections of massless shafting. Such a simplified model does not reproduce the exact dynamic characteristics of the actual system. In recent years several cases of marine crankshaft failures have been attributed to the phenomenon of secondary resonance, which is explained by the fact that the effective inertia of each slider crankmechanism varies about a mean value in relation to the position of the crank. When the variableinertia effect is allowed for, the equations of motion taking into account the effect are nonlinear. Assuming small displacements, the equations can be linearized to predict important characteristics of the motion. The motions in the form of complex wave forms are studied at different speeds of engine rotation and some of the wave form solutions are analyzed in the range of present investigations. Computer methods making use of numerical analysis processes, namely, the modifiedEuler's equations and the Runge-Kutta constants, have been applied in the investigations. A study of the effect on the motion of the system due to variation of inertia ratio is carried out at a particular speed of the crankshaft rotation; also investigated are the variations in the motions due to the action of external excitations with respect to changes in phase angle and inertia ratio. General comments on Draminsky's work in the light of the present investigations are included.

scholarly journals Temporal variation of seismicity and spectrum of small earthquakes preceding the 1952 Kern County, California, earthquake

1980 ◽  
Vol 70 (2) ◽  
pp. 509-527
Author(s):  
Mizuho Ishida ◽  
Hiroo Kanamori
Keyword(s):  
Stress Concentration ◽  
Temporal Variation ◽  
Main Shock ◽  
Fault Plane ◽  
Large Earthquake ◽  
Kern County ◽  
Epicentral Area ◽  
San Fernando ◽  
Spatio Temporal ◽  
Definite Indicator

abstract The spatio-temporal variation of seismicity in the epicentral area of the 1952 Kern County California, earthquake (Ms = 7.7, 34°58.6′N; 119°02′W) was examined for the period prior to the main shock. Most of the events that occurred in the epicentral area were relocated by using the main shock as a master event. A large part of the fault plane of the Kern County earthquake had been seismically quiet for nearly 15 yr before the main shock. However, the activity in the immediate vicinity of the epicenter had been very high during the same period. The temporal variation of the activity in the vicinity of the epicentral area exhibits a pattern very similar to that found for the 1971 San Fernando earthquake. During the 112 yr period immediately before the main shock, tight clustering of activity around the main-shock epicenter occurred. This clustering may be considered to be foreshock activity. This period of increased activity was preceded by a quiet period for 2 yr from 1949 to 1950; no event was located on the fault plane of the Kern County earthquake during this period. This pattern, quiescence followed by clustering, seems to have repeated several times prior to 1949. Thus, this pattern alone cannot be used as a definite indicator of a large earthquake, but in terms of a fault model with asperities, it can be a manifestation of progressive stress concentration toward the eventual hypocenter. Spectral analyses of the Pasadena Wood-Anderson seismograms of the events that occurred near the epicentral area showed that the frequency of the spectral peak is systematically higher for the foreshocks than the events prior to 1949. A similar trend was found for the 1971 San Fernando earthquake. These results are consistent with the model of stress concentration around the eventual hypocenter.

Spatial-temporal variation of seismicity and spectrum of the 1980 earthquake swarm near the Izu Peninsula, Japan

1984 ◽  
Vol 74 (1) ◽  
pp. 199-221
Author(s):  
Mizuho Ishida
Keyword(s):  
Temporal Variation ◽  
Main Shock ◽  
Earthquake Swarm ◽  
Maximum Pressure ◽  
Earthquake Activity ◽  
The South ◽  
Epicentral Area ◽  
Izu Peninsula ◽  
Wave Forms ◽  
Swarm Activity

Abstract The spatial-temporal variation of seismicity of the 1980 earthquake swarm off the east coast of the Izu Peninsula, Japan, was investigated. Hypocentral distribution, focal mechanism, wave forms, and spectra of seismic waves were studied. The hypocenters were relocated by using the master event method. The forerunning earthquakes which started about one week before the largest shock (main shock), the 1980 Izu-Hanto-Toho-Oki earthquake (M = 6.7), occurred within the quiescent area of the earthquake activity for the preceding one year. The swarm area migrated toward the south with time and triggered the main shock in June 1980. The fault dimension and geometry were estimated from the aftershock area: the fault length and width are 14 km and 8 km; the strike and dip angles of the fault are N15°W and 65° to N75°E. Locations of the events in an earlier earthquake swarm (1978) were also examined by using difference in the S-P time at five selected stations distributed around the epicentral area. The 1978 swarm events were found to have clustered within a very small area of 8 ×1 km2 located about 2 km to the west of the 1980 swarm area. The earthquakes which occurred after the main shock of the 1980 swarm were classified into two groups, aftershocks and swarm events, according to the location of epicenters, wave forms, and spectra of S waves. The peak frequencies of spectra were distributed around 5 to 8 Hz for the aftershocks and around 10 to 15 Hz for the swarm events. Most of the aftershocks, characterized by low-frequency content, occurred to the south of the main shock within 2 weeks after the main shock. The number of aftershocks decayed following the modified Omori's formula with p = 1.5 ± 0.3. The swarm activity, on the other hand, continued intermittently for about 1 month after the main shock. The 1980 seismic activity is interpreted as a complex of a foreshock-main shock-aftershock sequence and swarm activity. The direction of the longer axis of the swarm area coincided with the direction of the maximum pressure axis of the main shock. The trend of the aftershock zone coincided with the strike of the fault planes of the main shock and aftershocks. This feature strongly suggests that tension cracks trending in the maximum stress direction opened prior to the occurrence of the main shock. The opening of cracks may be accounted for by increasing of interstitial pore pressure associated with increase in regional stress.

Elastic displacements in the near-field of a propagating fault

1969 ◽  
Vol 59 (2) ◽  
pp. 865-908
Author(s):  
N. A. Haskell
Keyword(s):  
Fault Plane ◽  
Near Field ◽  
Strong Motion ◽  
Dislocation Motion ◽  
Displacement Discontinuity ◽  
Wave Form ◽  
Strong Motion Station ◽  
Ramp Function ◽  
Wave Forms ◽  
Parkfield Earthquake

abstract Displacement, particle velocity, and acceleration wave forms in the near field of a propagating fault have been computed by numerical integration of the Green's function integrals for an infinite medium. The displacement discontinuity (dislocation) on the fault plane is assumed to have the form of a unilaterally propagating finite ramp function in time. The calculated wave forms in the vicinity of the fault plane are quite similar to those observed at the strong motion station nearest the fault plane at the Parkfield earthquake. The comparison suggests that the propagating ramp time function is roughly representative of the main features of the dislocation motion on the fault plane, but that the actual motion has somewhat more high frequency complexity. Calculated amplitudes indicate that the average final dislocation on the fault at the Parkfield earthquake was more than an order of magnitude greater than the offsets observed on the visible surface trace. Computer generated wave form plots are presented for a variety of locations with respect to the fault plane and for two different assumptions on the relation between fault length and ramp function duration.

Some numerical solutions for Lamb's problem

1974 ◽  
Vol 64 (2) ◽  
pp. 473-491
Author(s):  
Harold M. Mooney
Keyword(s):  
Rayleigh Wave ◽  
Poisson’S Ratio ◽  
Pulse Width ◽  
Numerical Solutions ◽  
Pulse Height ◽  
P Wave ◽  
Poisson's Ratio ◽  
Wave Form ◽  
Lamb’S Problem ◽  
Wave Forms

abstract We consider a version of Lamb's Problem in which a vertical time-dependent point force acts on the surface of a uniform half-space. The resulting surface disturbance is computed as vertical and horizontal components of displacement, particle velocity, acceleration, and strain. The goal is to provide numerical solutions appropriate to a comparison with observed wave forms produced by impacts onto granite and onto soil. Solutions for step- and delta-function sources are not physically realistic but represent limiting cases. They show a clear P arrival (larger on horizontal than vertical components) and an obscure S arrival. The Rayleigh pulse includes a singularity at the theoretical arrival time. All of the energy buildup appears on the vertical components and all of the energy decay, on the horizontal components. The effects of Poisson's ratio upon vertical displacements for a step-function source are shown. For fixed shear velocity, an increase of Poisson's ratio produces a P pulse which is larger, faster, and more gradually emergent, an S pulse with more clear-cut beginning, and a much narrower Rayleigh pulse. For a source-time function given by cos2(πt/T), −T/2 ≦ T/2, a × 10 reduction in pulse width at fixed pulse height yields an increase in P and Rayleigh-wave amplitudes by factors of 1, 10, and 100 for displacement, velocity and strain, and acceleration, respectively. The observed wave forms appear somewhat oscillatory, with widths proportional to the source pulse width. The Rayleigh pulse appears as emergent positive on vertical components and as sharp negative on horizontal components. We show a theoretical seismic profile for granite, with source pulse width of 10 µsec and detectors at 10, 20, 30, 40, and 50 cm. Pulse amplitude decays as r−1 for P wave and r−12 for Rayleigh wave. Pulse width broadens slightly with distance but the wave form character remains essentially unchanged.

scholarly journals The Zagreb (Croatia) M5.5 Earthquake on 22 March 2020

Geosciences ◽  
2020 ◽  
Vol 10 (7) ◽  
pp. 252 ◽  
Author(s):  
Snježana Markušić ◽  
Davor Stanko ◽  
Tvrtko Korbar ◽  
Nikola Belić ◽  
Davorin Penava ◽  
...  
Keyword(s):  
Structural Engineering ◽  
Main Shock ◽  
Residential Buildings ◽  
Tectonic Setting ◽  
Time Lapse ◽  
Earthquake Sequence ◽  
Epicentral Area ◽  
Local Soil ◽  
Seismic Amplification ◽  
Zagreb Area

On 22 March 2020, Zagreb was struck by an M5.5 earthquake that had been expected for more than 100 years and revealed all the failures in the construction of residential buildings in the Croatian capital, especially those built in the first half of the 20th century. Because of that, extensive seismological, geological, geodetic and structural engineering surveys were conducted immediately after the main shock. This study provides descriptions of damage, specifying the building performances and their correlation with the local soil characteristics, i.e., seismic motion amplification. Co-seismic vertical ground displacement was estimated, and the most affected area is identified according to Sentinel-1 interferometric wide-swath data. Finally, preliminary 3D structural modeling of the earthquake sequence was performed, and two major faults were modeled using inverse distance weight (IDW) interpolation of the grouped hypocenters. The first-order assessment of seismic amplification (due to site conditions) in the Zagreb area for the M5.5 earthquake shows that ground motions of approximately 0.16–0.19 g were amplified at least twice. The observed co-seismic deformation (based on Sentinel-1A IW SLC images) implies an approximately 3 cm uplift of the epicentral area that covers approximately 20 km2. Based on the preliminary spatial and temporal analyses of the Zagreb 2020 earthquake sequence, the main shock and the first aftershocks evidently occurred in the subsurface of the Medvednica Mountains along a deep-seated southeast-dipping thrust fault, recognized as the primary (master) fault. The co-seismic rupture propagated along the thrust towards northwest during the first half-hour of the earthquake sequence, which can be clearly seen from the time-lapse visualization. The preliminary results strongly support one of the debated models of the active tectonic setting of the Medvednica Mountains and will contribute to a better assessment of the seismic hazard for the wider Zagreb area.

scholarly journals Technologies and new approaches used by the INGV EMERGEO Working Group for real-time data sourcing and processing during the Emilia Romagna (northern Italy) 2012 earthquake sequence

2012 ◽  
Vol 55 (4) ◽  
Author(s):  
Giuliana Alessio ◽  
Laura Alfonsi ◽  
Carlo Alberto Brunori ◽  
Pierfrancesco Burrato ◽  
Giuseppe Casula ◽  
...  
Keyword(s):  
Seismic Event ◽  
Main Shock ◽  
Northern Italy ◽  
Earthquake Activity ◽  
Seismic Sequence ◽  
Time Data ◽  
Broad Area ◽  
Epicentral Area ◽  
Po Plain ◽  
Real Time Data

<p>On May 20, 2012, a Ml 5.9 seismic event hit the Emilia Po Plain, triggering intense earthquake activity along a broad area of the Po Plain across the provinces of Modena, Ferrara, Rovigo and Mantova (Figure 1). Nine days later, on May 29, 2012, a Ml 5.8 event occurred roughly 10 km to the SW of the first main shock. These events caused widespread damage and resulted in 26 victims. The aftershock area extended over more than 50 km and was elongated in the WNW-ESE direction, and it included five major aftershocks with 5.1 ≤Ml ≤5.3, and more than 2000 minor events (Figure 1). In general, the seismic sequence was confined to the upper 10 km of the crust. Minor seismicity with depths ranging from 10 km to 30 km extended towards the southern sector of the epicentral area (ISIDe, http://iside.rm.ingv.it/). […]</p><br />

STUDIES OF DISTAL COLONIC MOTILITY IN CHILDREN

PEDIATRICS ◽  
1956 ◽  
Vol 17 (6) ◽  
pp. 820-833
Author(s):  
Murray Davidson ◽  
Marvin H. Sleisenger ◽  
Thomas P. Almy ◽  
Samuel Z. Levine
Keyword(s):  
Ulcerative Colitis ◽  
Bowel Movement ◽  
Colonic Motility ◽  
Distal Colon ◽  
Wave Form ◽  
Spontaneous Bowel Movement ◽  
Normal Individuals ◽  
Iced Water ◽  
Wave Forms

A characteristic propulsive wave, previously reported in adults with ulcerative colitis, has been found in infants with acute diarrhea but not in children with ulcerative colitis. The reasons for this are discussed. The induction of propulsive wave forms in normal individuals by administration of magnesium sulfate orally is described and attention is called to its application to therapeutic studies. The relation of this wave form to propulsion of fecal contents and defecation and its role in the production of abdominal discomfort are considered. Observed variations in the responses of individual children to subcutaneous injection of Mecholyl®, to oral administration of iced water, and to rectal distention may explain innate differences in susceptibility to the development of colonic symptoms in different children. A classification of wave forms from the distal colon based on current concepts of their probable physiologic significance is offered. A tracing from the distal colon in a child having a spontaneous bowel movement is presented and commented on.

Source comparisons between nuclear and chemical explosions detonated at Rainier Mesa, Nevada Test Site

1999 ◽  
Vol 89 (2) ◽  
pp. 409-422 ◽  
Author(s):  
Brian W. Stump ◽  
D. Craig Pearson ◽  
Robert E. Reinke
Keyword(s):  
Source Region ◽  
Spectral Ratio ◽  
Test Site ◽  
Source Model ◽  
Transverse Component ◽  
Propagation Path ◽  
Cube Root ◽  
Nevada Test Site ◽  
Spectral Difference ◽  
Receiver Array

Abstract A series of nuclear [MINERAL QUARRY (MQ), HUNTERS TROPHY (HT)] and chemical [NON-PROLIFERATION EXPERIMENT (NPE) and NPECAL] explosions were detonated in the same geological material at Rainier Mesa, Nevada Test Site. These sources were extensively instrumented with the same near-source, free-surface instrumentation array. The data from these explosions allow the establishment of empirical source scaling relations as well as investigation of possible chemical and nuclear source differences. Even in the near-source region at common receivers, the data display propagation path effects resulting from slight differences in source locations. These effects are effectively taken into account by smoothing the source comparisons across the different stations in the receiver array. As many as 30 individual waveforms from each source are used in this smoothing process. Comparison of HT and NPE at near-source distances indicates that within the bandwidth of the data (0.36 to 100 Hz), there is no apparent spectral difference between the nuclear and single-fired chemical source. The smoothed spectral ratio between the NPE and NPE CAL is consistent with the long-period source spectral difference (104), corner frequencies (2 to 3 Hz/NPE and 40 to 60 Hz/NPE CAL), and high-frequency decay (ƒ−2) similar to the Mueller-Murphy source model for wet tuff after modifying the cavity radius to scale as the cube root of yield. Comparison of the two nuclear sources, HT and MQ, indicates that at long periods, the HT/MQ ratio is 0.4 to 0.6 with the spectra from the two explosions merging above 5 Hz, which is consistent with the 0.3 magnitude difference observed for the two sources. In all the source comparisons, the spectral ratios of the transverse components of motion are indistinguishable from those produced by either the vertical or radial components. This fact argues that the transverse component of motion from an explosion is generated at very close-in distances, in this case on the order of 1 to 2 km. These observations are in agreement with some type of linear scattering mechanism.

Bioelectric Regulation of Tentacle Movement in a Dinoflagellate

1967 ◽  
Vol 47 (3) ◽  
pp. 433-446
Author(s):  
ROGER ECKERT ◽  
TAKAO SIBAOKA
Keyword(s):  
Temporal Relationship ◽  
Sea Water ◽  
Outward Current ◽  
Wave Form ◽  
Applied Current ◽  
Inward Current ◽  
Wave Forms ◽  
Noctiluca Miliaris ◽  
Spike Wave ◽  
Peripheral Cytoplasm

1. Recurring extensions and flexions of the food-gathering tentacle of Noctiluca miliaris occur spontaneously. Identical movements can be evoked by appropriate electrical stimulation. 2. Spontaneous recurring potential wave forms (TRPs) were recorded from the vacuole of the luminescent form of Noctiluca during movements of the tentacle. The basic TRP wave form consists of a characteristic negative-going spike which arises at -20 to -30 mV. from the slowly redeveloping negativity of a pre-spike depolarization, and is followed by a quasi-stable post-spike d.c. level of relative vacuolar negativity (-45 to -60 mV.). 3. The TRP complex, similar in shape to that which occurs spontaneously, follows an intracellularly applied current pulse of either polarity if the vacuolar potential is at the post-spike level. The duration of the evoked pre-spike wave is related to the current intensity and duration. During the pre-spike state outward current is ineffective, although a TR spike occurs in response to inward current. 4. The TRP is distinct in its behaviour and wave form from the flash-triggering potential, which can be evoked in the same cell, even though both exhibit all-or-none spikes. 5. Simultaneous recordings of intracellular potentials and movements of the tentacle showed a consistent temporal relationship between potential changes and subsequent movement. Extension of the tentacle begins 1-2 sec. after the spike and flexion begins within 1 sec. after beginning of the pre-spike wave. 6. Tentacle movement ceased in Ca-free sea water even though the cyclic potential changes continued normally. 7. Electron micrographs of the tentacle showed longitudinal aggregations of microtubules near the outer surface of the peripheral cytoplasm. It is proposed that contraction of these microtubules is the immediate cause of tentacle movements.

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