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Author: Shri Krishna Singh

Magnitude and Epicenter Estimations of Mexican Earthquakes form Isoseismic Maps

Shri Krishna Singh (1980)

Relationships between magnitude, M, and areas, Ai, of modified intensity contours IV, V and VI of the form M = Î»i log Ai + Âµi are derived from Mexican earthquakes. Due to insufficient data, Î»i has been fixed to 1. Events have been grouped broadly as interplate and intraplate events. Within the range of their validity (7.0â‰¤ M â‰¤8.2 for interplate; 6.4 â‰¤ M â‰¤ 7.1 for intraplate) the relations would give estimate of M to within Â± 0.3 to Â± 0.4 unit ( one standard deviation) of magnitude. The attenuation of intensity for interplate earthquakes is higher than that for intraplate earthquakes. The attenuation for interplate earthquakes is comparable to or greater than for Southern California earthquakes. Epicenters estimated at the center of maximum intensity contours differ from instrumental epicenter bye 48 Â± 22 km.

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Magnitude Epicenter Mexican Earthquakes Isoseismic Maps Magnitude Epicenter Mexican Earthquakes Isoseismic Maps concept8601 Seismology CIENCIAS FÍSICO MATEMÁTICAS Y CIENCIAS DE LA TIERRA CIENCIAS DE LA TIERRA Y DEL ESPACIO GEOFÍSICA SISMOLOGÍA Y PROSPECCIÓN SÍSMICA

PREMONITORY ELEVATION CHANGE BEFORE AN EARTHQUAKE BASED ON DILATANCY-DIFFUSION MODEL

Shri Krishna Singh (1973)

The dilatancy-diffusion model, recently proposed to explain premonitory changes in geo-physical and geochemical fields before several shallow earthquakes, implies uplift of the epicentral region. Based on a dilating sphere in an elastic half-space, simple formulas and a graph are presented which could be used to predict the magnitude and depth of the focus of a future earthquake if the magnitude of the dilatancy were known. Alternatively an estímate of the magnitude of the dilatancy can be made with the help of the graph by compiling information on maximum vertical displacement, depth of the center and the radius of the dilating sphere for earthquakes that are preceded by dilatancy.

Article

Premonitory Elevation Change Earthquake Dilatancy-Diffusion Model Premonitory Elevation Change Earthquake Dilatancy-Diffusion Model Seismology concept8601 Seismology CIENCIAS FÍSICO MATEMÁTICAS Y CIENCIAS DE LA TIERRA CIENCIAS DE LA TIERRA Y DEL ESPACIO GEOFÍSICA SISMOLOGÍA Y PROSPECCIÓN SÍSMICA

TRANSIENT ELECTROMAGNETIC RESPONSE OF A CONDUCTING INFINITE CYLINDER EMBEDDEN IN A CONDUCTING MEDIUM

Shri Krishna Singh (1972)

Transient electromagnetic response of a conducting permeable cylinder embedded in a conducting infinite space is obtained in the form of definite integrals. The source is an infinite insulated cable which ties outside the cylinder and carries a Heaviside current. The displacement currents have been neglected. Expression for transient response function under quasi-static approximation is also given.

Article

Transient Electromagnetic Response Conducting Cylinder Transient Electromagnetic Response Conducting Cylinder Seismology concept8601 Seismology CIENCIAS FÍSICO MATEMÁTICAS Y CIENCIAS DE LA TIERRA CIENCIAS DE LA TIERRA Y DEL ESPACIO GEOFÍSICA SISMOLOGÍA Y PROSPECCIÓN SÍSMICA

Shri Krishna Singh (1972)

Numerical results for the transient electromagnetic response of a conducting infinite cylinder embedded in a conducting medium excited by a infinite line source are presented. The input current is a Heaviside function of time. The displacement currents are summed to be negligible in comparison with the conduction currents. The contribution of n = 0 term (induced line current in the cylinder) is shown to predominate over the higher multipoles .As a rough rule the effect of the outer conductivity must be taken into consideration if it is more than 10 -2 times the conductivity of the cylinder.

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Transient Electromagnetic Respoonse Cylinder In A Conducting Transient Electromagnetic Respoonse Cylinder In A Conducting Seismology concept8601 Seismology CIENCIAS FÍSICO MATEMÁTICAS Y CIENCIAS DE LA TIERRA CIENCIAS DE LA TIERRA Y DEL ESPACIO GEOFÍSICA SISMOLOGÍA Y PROSPECCIÓN SÍSMICA

SHALLOW CRUSTAL STRUCTURE BELOW MEXICO CITY

Shri Krishna Singh (1978)

From unreversed seismic refraction profiles, using quarry blasts as source, a 2-layer upper crustal structure below México City is obtained: for the first layer (2 km thick) Î±1 (the compressional wave velocity) =2.9 km/sec, for the second layer Î±2=4.7 km/sec. These values compare reasonably well the values obtained in the lake of Texcoco from short reversed refraction profiles.

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Shallow Crustal Structure Shallow Crustal Structure Seismology concept8601 Seismology CIENCIAS FÍSICO MATEMÁTICAS Y CIENCIAS DE LA TIERRA CIENCIAS DE LA TIERRA Y DEL ESPACIO GEOFÍSICA SISMOLOGÍA Y PROSPECCIÓN SÍSMICA

Intraslab versus interplate earthquakes as recorded in Mexico City: implications for seismic hazard

Shri Krishna Singh (2013)

We study the relative importance of interplate and intraslab earthquakes in the seismic hazard of Mexico City by analyzing accelerograms recorded at the hill-zone site of CU (1964-2012) and the lake-bed site of SCT (1985-2012). A(max) exceeded 6 gal during 20 earthquakes at CU during this period. Of these, eight were intraslab events so that the exceedance rate of A(max) >= 6 gal from both types of earthquakes is roughly about the same. The estimated return period of A(max) of 30 gal from the two types of earthquakes is similar to 100 yrs. If we consider high-frequency (2.5-8.5 Hz) acceleration (A(max)(HF)) at CU, then the top 7 out of the 20 events are all intraslab earthquakes. Even at the lake-bed site of SCT, the A(max)(HF) values are, generally, associated with intraslab earthquakes. It follows that the risk from both types of earthquakes to low-rise construction in the city needs careful assessment.

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TERREMOTOS DE PROFUNDIDAD INTERMEDIA ZONAS DE SUBDUCCIÓN ACOPLADAS TERREMOTOS INSLAB VARIACIÓN TEMPORAL TRANSFERENCIA DE ESTRÉS SPECTRA CICLO TEMPORARY VARIATION COUPLED SUBDUCTION ZONES INTERMEDIATE DEPTH EARTHQUAKES CIENCIAS FÍSICO MATEMÁTICAS Y CIENCIAS DE LA TIERRA CIENCIAS DE LA TIERRA Y DEL ESPACIO GEOFÍSICA SISMOLOGÍA Y PROSPECCIÓN SÍSMICA concept8601 Seismology

Magnitude determination of Mexican earthquakes

Shri Krishna Singh (1994)

We explore two altemative magnitude scales, MA and ME, for quasi-real time estimate of magnitude of moderate and large Mexican earthquakes using broadband recordings at Ciudad Universitaria (CU), Mexico D.F., Mexico. MA and Me are based on amplitude of band-pass filtered (between 15 and 30 sec) velocity traces and estimate of radiated seismic energy, respectively. Both scales are tied to the moment magnitude, MW. MA is adequate for shallow, moderate, and large earthquakes, but appears to saturate for major and great earthquakes. ME, on the other hand, does not suffer from saturation and should be valid for events of all depths. In as much as MA measures long-period characteristics of an event while the contribution to ME mostly comes from frequencies near the comer frequency of the event, the magnitude on the two scales may differ for the same earthquake, even if MA has not saturated. Since a large disparity in the two magnitudes may be indicative of anomalous nature of an earthquake, we recommend the use of both scales whenever possible.

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Magnitude scále Seismic energy Amplitude Escala de magnitud Energía sísmica Amplitud Magnitude scále Seismic energy Amplitude Seismology concept8601 Seismology CIENCIAS FÍSICO MATEMÁTICAS Y CIENCIAS DE LA TIERRA CIENCIAS DE LA TIERRA Y DEL ESPACIO GEOFÍSICA SISMOLOGÍA Y PROSPECCIÓN SÍSMICA

The earthquake of 16 November, 1925 (Ms=7.0) and the reported tsunami in Zihuatanejo, Mexico

Shri Krishna Singh (1998)

A feasibility study to develop a tsunami alert system for Mexican earthquakes, using broadband seismograms from the National Seismological Service, is currently under way. A first step in this direction is a revision of the Mexican tsunami catalogs. In these catalogs, one of the largest tsunamis of this century is reported in the Port of Zihuatanejo and has been re- lated to an earthquake which occurred on November 16, 1925. This earthquake was located at a distance of about 600 km from Zihuatanejo and had a surface-wave magnitude, Ms, of 7.0. In developing a tsunami alert system, it is important t o know if the tsunami was indeed related to the earthquake of 1925. In this note we examine available evidence and find thatthe tsunami was not related to the earthquake. There is no evidence of a local earthquake near Zihuatanejo which may have resulted in the tsunami. We conclude that the tsunami was either caused by slumping of the sea floor near Zihuatanejo or by a meteorological phenomenon in the region.

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Tsunami of 1925 Tsunami in Zihuatanejo Earthquake Tsunami of 1925 Tsunami in Zihuatanejo Earthquake Seismology concept8601 Seismology CIENCIAS FÍSICO MATEMÁTICAS Y CIENCIAS DE LA TIERRA CIENCIAS DE LA TIERRA Y DEL ESPACIO GEOFÍSICA SISMOLOGÍA Y PROSPECCIÓN SÍSMICA

Shri Krishna Singh (2007)

The empirical Green's function (EGF) technique is frequently used to estimate the radiated seismic energy, ER, of an earthquake. An approximation of the moment-rate spectrum, M0(f), of the target earthquake is obtained from the ratio of the spectrum of the target earthquake to the spectrum of the EGF earthquake, and the radiated seismic energy is computed by integrating f2M0 2(f) over frequency f. The choice of the upper limit of integration, fu, is critical. In this note we show that the optimum choice of fu, for the ω2-source model is given by fu/fc1∼ fc2/fc1, where fc1 and fc2 are the corner frequencies of the target and the EGF earthquakes, respectively. This result provides a useful guide in the application of the EGF technique to obtain a reliable estimate of the radiated seismic energy.

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TERREMOTOS ANÁLISIS EMPÍRICO MÉTODO DE ESTIMACIÓN FUNCIÓN VERDE ANÁLISIS DE FIABILIDAD SISMICIDAD Earthquake Empirical analysis Estimation method Green function Reliability analysis Seismicity CIENCIAS FÍSICO MATEMÁTICAS Y CIENCIAS DE LA TIERRA CIENCIAS DE LA TIERRA Y DEL ESPACIO GEOFÍSICA SISMOLOGÍA Y PROSPECCIÓN SÍSMICA concept8601 Seismology