The Managua, Nicaragua, earthquake of December 23, 1972: Location, focal mechanism, and intensity distribution

1974 ◽  
Vol 64 (4) ◽  
pp. 993-1004
Author(s):  
S. T. Algermissen ◽  
J. W. Dewey ◽  
C. J. Langer ◽  
W. H. Dillinger
Keyword(s):  
Main Shock ◽  
Strong Motion ◽  
Strike Slip ◽  
Maximum Intensity ◽  
Central American ◽  
P Wave ◽  
Benioff Zone ◽  
Depth Of Focus ◽  
Source Effects ◽  
The City

abstract The Managua earthquake occurred at a shallow depth of focus beneath the center of Managua, producing a maximum intensity of MM IX in the center of the city. The epicenter of the main shock is determined to within several kilometers by use of the strong-motion accelerogram recorded at the ESSO refinery. Such accuracy is unprecedented for a large Central American earthquake, and makes the Managua earthquake valuable as a calibration event for minimizing the bias in location of other earthquakes in Nicaragua. The character of the distribution of P-wave residuals and the location of the earthquake well inland from the Benioff zone in Nicaragua suggest that much of the bias in epicenters calculated for earthquakes in the vicinity of Managua is due to station effects rather than source effects. P-wave first-motions are consistent with a left-lateral strike-slip fault as the earthquake source.

Control of rupture by fault geometry during the 1966 parkfield earthquake

1981 ◽  
Vol 71 (1) ◽  
pp. 95-116 ◽  
Author(s):  
Allan G. Lindh ◽  
David M. Boore
Keyword(s):  
Main Shock ◽  
Fault Plane ◽  
San Andreas Fault ◽  
Strong Motion ◽  
P Wave ◽  
Fault Geometry ◽  
Dynamic Rupture ◽  
San Andreas ◽  
Hill Station ◽  
Parkfield Earthquake

abstract A reanalysis of the available data for the 1966 Parkfield, California, earthquake (ML=512) suggests that although the ground breakage and aftershocks extended about 40 km along the San Andreas Fault, the initial dynamic rupture was only 20 to 25 km in length. The foreshocks and the point of initiation of the main event locate at a small bend in the mapped trace of the fault. Detailed analysis of the P-wave first motions from these events at the Gold Hill station, 20 km southeast, indicates that the bend in the fault extends to depth and apparently represents a physical discontinuity on the fault plane. Other evidence suggests that this discontinuity plays an important part in the recurrence of similar magnitude 5 to 6 earthquakes at Parkfield. Analysis of the strong-motion records suggests that the rupture stopped at another discontinuity in the fault plane, an en-echelon offset near Gold Hill that lies at the boundary on the San Andreas Fault between the zone of aseismic slip and the locked zone on which the great 1857 earthquake occurred. Foreshocks to the 1857 earthquake occurred in this area (Sieh, 1978), and the epicenter of the main shock may have coincided with the offset zone. If it did, a detailed study of the geological and geophysical character of the region might be rewarding in terms of understanding how and why great earthquakes initiate where they do.

The 19 August 1976 Denizli, Turkey, earthquake: Evaluation of the strong motion accelerograph record

1982 ◽  
Vol 72 (5) ◽  
pp. 1635-1649
Author(s):  
Ref'an Can Ates ◽  
Nejat Bayülke
Keyword(s):  
Structural Design ◽  
High Frequency ◽  
Strong Motion ◽  
Maximum Intensity ◽  
Peak Acceleration ◽  
Natural Period ◽  
High Rise ◽  
The City ◽  
Heavy Damage ◽  
Epicentral Region

abstract On 19 August 1976, Denizli city, located at the southwest of Anatolia, was shaken by an earthquake with a magnitude 4.7 (ISC determination). The earthquake destroyed 40 houses, damaged 1284 houses heavily, and caused a loss of live of four persons. Maximum intensity of MM VI+ was observed at the city of Denizli with a population of 110,000. The strong motion accelerograph (SMA-1 Kinemetrics) installed at Denizli recorded the ground motion. This is the first strong motion record obtained in Turkey at the epicentral region of the earthquake. The strong motion accelerogram, digitized on a Bendix digitizer, baseline correction was calculated, and the acceleration, velocity, and displacement spectrums were obtained. The peak acceleration values were 0.27 g eastwest, 0.34 g north-south, and 0.21 g in vertical components of the record; relatively high for a magnitude 4.7 earthquake. Denizli is a very developed West Anatolian city with high-rise buildings with modern structural design. It was calculated that the natural period of the buildings damaged due to the earthquake of the 19 August was high. Therefore, heavy damage on the buildings of the short natural period can be attributed to the high-frequency large-amplitude ground accelerations of the Denizli earthquake.

scholarly journals The July 27, 1976 Tangshan, China earthquake—A complex sequence of intraplate events

1979 ◽  
Vol 69 (1) ◽  
pp. 207-220 ◽  
Author(s):  
Rhett Butler ◽  
Gordon S. Stewart ◽  
Hiroo Kanamori
Keyword(s):  
Surface Waves ◽  
Seismic Moment ◽  
Main Shock ◽  
Normal Fault ◽  
Strike Slip ◽  
Body Waves ◽  
P Wave ◽  
Tangshan Earthquake ◽  
Total Moment ◽  
Slip Event

abstract The Tangshan earthquake (Ms = 7.7), of July 27, 1976 and its principal aftershock (Ms = 7.2), which occurred 15 hr following the main event, resulted in the loss of life of over 650,000 persons in northeast China. This is the second greatest earthquake disaster in recorded history, following the 1556 Shensi Province, Chinese earthquake in which at least 830,000 persons lost their lives. Detailed analyses of the teleseismic surface waves and body waves are made for the Tangshan event. The major conclusions are: (1) The Tangshan earthquake sequence is a complex one, including strike-slip, thrust, and normal-fault events. (2) The main shock, as determined from surface waves, occurred on a near vertical right-lateral strike-slip fault, striking N40°E. (3) A seismic moment of 1.8 × 1027 dyne-cm is obtained. From the extent of the aftershock zone and relative location of the main shock epicenter, symmetric (1:1) bilateral faulting with a total length of 140 km may be inferred. If a fault width of 15 km is assumed, the average offset is estimated to be 2.7 meters with an average stress drop of about 30 bars. (4) The main shock was initiated by an event with a relatively slow onset and a seismic moment of 4 × 1026 dyne-cm. The preferred fault-plane solution, determined from surface-wave analyses, indicates a strike 220°, dip 80°, and rake −175°. (5) Two thrust events follow the strike-slip event by 11 and 19 sec, respectively. They are located south to southwest of the initial event and have a total moment of 8 × 1025 dyne-cm. This sequence is followed by several more events. (6) The principal aftershock was a normal-fault double event with the fault planes unconstrained by the P-wave first motions. Surface waves provide additional constraints to the mechanism to yield an oblique slip solution with strike N120°E, dip 45°SW, and rake −30°. A total moment of 8 × 1026 dyne-cm is obtained. (7) The triggering of lesser thrust and normal faults by a large strike-slip event in the Tangshan sequence has important consequences in the assessment of earthquake hazard in other complex strike-slip systems like the San Andreas.

THE EMPIRICAL GREEN’S FUNCTION TECHNIQUE MODIFICATION FOR ACCELEROGRAM SYNTHESIS IN LOWSEISMICITY REGIONS

2018 ◽  
Vol 12 (5-6) ◽  
pp. 72-80
Author(s):  
A. A. Krylov
Keyword(s):  
Green’S Function ◽  
Green's Function ◽  
Main Shock ◽  
Amplitude Spectrum ◽  
Strong Motion ◽  
Function Technique ◽  
Focal Region ◽  
Empirical Green’S Function ◽  
Epicentral Zone ◽  
Empirical Green's Function

In the absence of strong motion records at the future construction sites, different theoretical and semi-empirical approaches are used to estimate the initial seismic vibrations of the soil. If there are records of weak earthquakes on the site and the parameters of the fault that generates the calculated earthquake are known, then the empirical Green’s function can be used. Initially, the empirical Green’s function method in the formulation of Irikura was applied for main shock record modelling using its aftershocks under the following conditions: the magnitude of the weak event is only 1–2 units smaller than the magnitude of the main shock; the focus of the weak event is localized in the focal region of a strong event, hearth, and it should be the same for both events. However, short-termed local instrumental seismological investigation, especially on seafloor, results usually with weak microearthquakes recordings. The magnitude of the observed micro-earthquakes is much lower than of the modeling event (more than 2). To test whether the method of the empirical Green’s function can be applied under these conditions, the accelerograms of the main shock of the earthquake in L'Aquila (6.04.09) with a magnitude Mw = 6.3 were modelled. The microearthquake with ML = 3,3 (21.05.2011) and unknown origin mechanism located in mainshock’s epicentral zone was used as the empirical Green’s function. It was concluded that the empirical Green’s function is to be preprocessed. The complex Fourier spectrum smoothing by moving average was suggested. After the smoothing the inverses Fourier transform results with new Green’s function. Thus, not only the amplitude spectrum is smoothed out, but also the phase spectrum. After such preliminary processing, the spectra of the calculated accelerograms and recorded correspond to each other much better. The modelling demonstrate good results within frequency range 0,1–10 Hz, considered usually for engineering seismological studies.

scholarly journals Determination of near-fault impulsive signals with multivariate naïve Bayes method

2021 ◽  
Author(s):  
Deniz Ertuncay ◽  
Giovanni Costa
Keyword(s):  
Naive Bayes ◽  
Strong Motion ◽  
Naïve Bayes ◽  
Strike Slip ◽  
Naive Bayes Classifier ◽  
Bayes Classifier ◽  
Naïve Bayes Classifier ◽  
Earthquake Physics ◽  
Near Fault ◽  
A Site

AbstractNear-fault ground motions may contain impulse behavior on velocity records. To calculate the probability of occurrence of the impulsive signals, a large dataset is collected from various national data providers and strong motion databases. The dataset has a large number of parameters which carry information on the earthquake physics, ruptured faults, ground motion parameters, distance between the station and several parts of the ruptured fault. Relation between the parameters and impulsive signals is calculated. It is found that fault type, moment magnitude, distance and azimuth between a site of interest and the surface projection of the ruptured fault are correlated with the impulsiveness of the signals. Separate models are created for strike-slip faults and non-strike-slip faults by using multivariate naïve Bayes classifier method. Naïve Bayes classifier allows us to have the probability of observing impulsive signals. The models have comparable accuracy rates, and they are more consistent on different fault types with respect to previous studies.

The San Salvador Earthquake of October 10, 1986—Seismological Aspects and Other Recent Local Seismicity

1987 ◽  
Vol 3 (3) ◽  
pp. 419-434 ◽  
Author(s):  
Randall A. White ◽  
David H. Harlow ◽  
Salvador Alvarez
Keyword(s):  
Main Shock ◽  
Fault Plane ◽  
Vertical Plane ◽  
Aftershock Sequence ◽  
Central American ◽  
Fault Plane Solution ◽  
San Salvador ◽  
The North ◽  
Volcanic Chain ◽  
Plane Solution

The San Salvador earthquake of October 10, 1986 originated along the Central American volcanic chain within the upper crust of the Caribbean Plate. Results from a local seismograph network show a tectonic style main shock-aftershock sequence, with a magnitude, Mw, 5.6. The hypocenter was located 7.3 km below the south edge of San Salvador. The main shock ruptured along a nearly vertical plane toward the north-northeast. A main shock fault-plane solution shows a nearly vertical fault plane striking N32\sz\E, with left-lateral sense of motion. This earthquake is the second Central American volcanic chain earthquake documented with left-lateral slip on a fault perpendicular to the volcanic chain. During the 2 1/2 years preceeding the earthquake, minor microseismicity was noted near the epicenter, but we show that this has been common along the volcanic chain since at least 1953. San Salvador was previously damaged by a volcanic chain earthquake on May 3, 1965. The locations of six foreshocks preceding the 1965 shock show a distinctly WNW-trending distribution. This observation, together with the distribution of damage and a fault-plane solution, suggest that right-lateral slip occurred along a fault sub-parallel with Central American volcanic chain. We believe this is the first time such motion has been documented along the volcanic chain. This earthquake was also unusual in that it was preceded by a foreshock sequence more energetic than the aftershock sequence. Earlier this century, on June 08, 1917, an Ms 6.4 earthquake occurred 30 to 40 km west of San Salvador Volcano. Only 30 minutes later, an Ms 6.3 earthquake occurred, centered at the volcano, and about 35 minutes later the volcano erupted. In 1919 an Ms 6 earthquake occurred, centered at about the epicenter of the 1986 earthquake. We conclude that the volcanic chain is seismically very active with variable styles of seismicity.

Aftershocks of the February 21, 1973 Point Mugu, California earthquake

1976 ◽  
Vol 66 (6) ◽  
pp. 1931-1952
Author(s):  
Donald J. Stierman ◽  
William L. Ellsworth
Keyword(s):  
Fault Zone ◽  
Main Shock ◽  
Fault Plane ◽  
Body Wave ◽  
P Wave ◽  
Fault System ◽  
Wave Radiation ◽  
Fault Plane Solutions ◽  
Complex Deformation ◽  
Transverse Ranges

abstract The ML 6.0 Point Mugu, California earthquake of February 21, 1973 and its aftershocks occurred within the complex fault system that bounds the southern front of the Transverse Ranges province of southern California. P-wave fault plane solutions for 51 events include reverse, strike slip and normal faulting mechanisms, indicating complex deformation within the 10-km broad fault zone. Hypocenters of 141 aftershocks fail to delineate any single fault plane clearly associated with the main shock rupture. Most aftershocks cluster in a region 5 km in diameter centered 5 km from the main shock hypocenter and well beyond the extent of fault rupture estimated from analysis of body-wave radiation. Strain release within the imbricate fault zone was controlled by slip on preexisting planes of weakness under the influence of a NE-SW compressive stress.

The 2019 Ms 4.2 and 5.2 Beiliu Earthquake Sequence in South China: Complex Conjugate Strike-Slip Faulting Revealed by Rupture Directivity Analysis

2021 ◽  
Author(s):  
Xiaohui He ◽  
Hao Liang ◽  
Peizhen Zhang ◽  
Yue Wang
Keyword(s):  
South China ◽  
Source Parameters ◽  
Active Faults ◽  
Fault Zones ◽  
Strike Slip ◽  
P Wave ◽  
Complex Conjugate ◽  
South China Block ◽  
Rupture Directivity ◽  
Time Duration

Abstract The South China block has been one of the most seismically quiescent regions in China, and the geometries and activities of the Quaternary faults have remained less studied due to the limited outcrops. Thus, source parameters of small-to-moderate earthquakes are important to help reveal the location, geometry distribution, and mechanical properties of the subsurface faults and thus improve the seismic risk assessment. On 12 October 2019, two earthquakes (the Ms 4.2 foreshock and the Ms 5.2 mainshock) occurred within 2 s and are located in southern South China block, near the junction region of the large-scale northeast-trending fault zones and the less continuous northwest-trending fault zones. We determined the point-source parameters of the two events via P-wave polarity analysis and regional waveform modeling, and the resolved focal mechanisms are significantly different with the minimum 3D rotation angle of 52°. We then resolved the rupture directivity of the two events by analyzing the azimuth variation of the source time duration and found the Ms 4.2 foreshock ruptured toward north-northwest for ∼1.0 km, and the Ms 5.2 mainshock ruptured toward east-southeast (ESE) for ∼1.5 km, implying conjugate strike-slip faulting. The conjugate causative faults have not been mapped on the regional geological map, and we infer that the two faults may be associated with the northwest-trending Bama-Bobai fault zone (the Shiwo section). These active faults are optimally oriented in the present-day stress field (northwest-southeast) and thus may now be potentially accumulating elastic strain to be released in a future large earthquake.

The June 13, 1975 earthquake and its relationship to the New Madrid seismic zone

1977 ◽  
Vol 67 (1) ◽  
pp. 209-218
Author(s):  
R. B. Herrmann ◽  
G. W. Fischer ◽  
J. E. Zollweg
Keyword(s):  
Parameter Estimation ◽  
Seismic Moment ◽  
Strong Motion ◽  
P Wave ◽  
Eastern North America ◽  
New Madrid Seismic Zone ◽  
Seismic Zone ◽  
Long Period ◽  
Consistent Solution ◽  
New Madrid

abstract The June 13, 1975 earthquake in the New Madrid seismic zone produced the first recorded strong-motion accelerograms for an event in the region, as well as the largest recorded accelerations to date for any event in eastern North America. The peak strong-motion values obtained from an analysis of the accelerograms are the following: amax = 43 cm/sec2, vmax = 1 cm/sec and dmax = 0.05 cm for the longitudinal S88°W component; amax = 31 cm/sec2, vmax = 0.6 cm/sec and dmax = 0.01 cm for the DOWN component; amax = 64 cm/sec2, vmax = 1.6 cm/sec2, and dmax = 0.09 cm for the tangential S02°E component. Source parameter estimation using long-period surface waves, Lg spectra, P-wave first motions and the integrated accelerograms leads to a consistent solution. The seismic moment is estimated to be 4E21 dyne-cm and the corner period 0.6 sec. The corner period-seismic moment pair for this event agrees with the regional scaling of these parameters observed by Street et al. (1975).

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