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Interaction of Cocos and rivera plates with the upper-mantle transition zone underneath central Mexico.

XYOLI PEREZ CAMPOS (2014)

Receiver functions (RFs) from 224 permanent and temporary stations in central and southern Mexico were used to characterize the upper-mantle transition zone in that region. Discontinuities at 410 and 660 km depth are both deeper compared to iasp91, which reflects a slow velocity anomaly in the upper mantle. They show topography on the interfaces that is consistent with the interaction of the subducted slab or its broken off extension. A low-velocity layer on top of the 410 is identified mainly on the continental side of where the slab pierces it (i.e. in the lee of the slab roll-back). In general the RFs show a complex behaviour where the mantle has been disturbed by the lateral motion of the subducted slab, and are simple where it has not. Complexity on the 660 coincides with the place where the broken off portion of the Farallon Plate would have penetrated this interface or is possibly lying on top of it.

Article

MANTO DE PROCESOS TRANSICIONES DE FASE NORTEAMÉRICA Volcanic Belt Shallow earthquakes Waves Seismology concept8601 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

Moment Tensor Catalog for Mexican Earthquakes: Almost Two Decades of Seismicity

Sara Franco (2020)

In this work we used waveforms and the catalog of National Seismological Service(SSN) to analyze more than 20,000 events with M>= 4.0 for the period2000-2018 with the goal of determining their moment tensor solutions. Because oflarge number of events, we automatize the process based on a set criteria. Usingepicentral location and magnitude of each earthquake reported by the SSN, a setof valid stations to be used for the moment solution, the length of time series,and the filter band for data and synthetics are automatically selected. Toexpedite calculations a pre-computed library of Green functions is used.

Through a linear inversion, for three-station combinations, the observed data andthe corresponding Green functions are used to determine the seismic momenttensor (with null isotropic component). To reduce a possible bias related to thestation distribution, each solution is weightened as a function of the azimuthalcoverage of the stations used. After the automatic process solutions of only8,000 earthquakes could be obtained; other events were rejected because ofincomplete length of the data segment and/or its integrity.

The solution quality is measured by the variance reduction value (VR). Astatistical analysis of quality allows us to establish a VR value of ≥ 50% asreasonable threshold for reliable solutions. With these criteria a catalog of ~1,500 events have been compiled, including some small events (Mw < 4.0).

There is evidence that show that the location of the well-solved events matchesthe areas of higher density of seismologic stations, and the limits of tectonicplates as well. A comparison between the catalog here obtained and the GlobalCentroid Moment Tensor (GCMT) catalog shows similarities. However, the magnitudereported in our catalog is systematically smaller than those reported byGCMT.

The moment tensor solution catalog is available online in a public database(132.248.6.13/~cmt). This work is the first in Mexico in which a database ofthis kind is presented.

Article

Moment Tensor Catalog Mexican Earthquakes Seismicity Moment Tensor Catalog Mexican Earthquakes Seismology concept8601 Seismology CIENCIAS FÍSICO MATEMÁTICAS Y CIENCIAS DE LA TIERRA CIENCIAS DE LA TIERRA Y DEL ESPACIO GEOFÍSICA SISMOLOGÍA Y PROSPECCIÓN SÍSMICA

The silent earthquake of 2002 in the Guerrero seismic gap, Mexico (Mw=7.6): inversion of slip on the plate interface and some implications

Arturo Iglesias (2003)

We invert GPS position data to map the slip on the plate interface during an aseismic, slow-slip event, which occurred in 2002 in the Guerrero seismic gap of the Mexican subduction zone, lasted for ∼4 months, and was detected by 7 continuous GPS receivers located over an area of ∼550×250 km2. Our best model, under physically reasonable constraints, shows that the slow slip occurred on the transition zone at a distance range of 100 to 170 km from the trench. The average slip was about 22.5 cm (Mo∼2.97 ×1027 dyne-cm, Mw=7.6). This model implies an increased shear stress at the bottom of the locked, seismogenic part of the interface which lies updip from the transition zone, and, hence. an enhanced seismic hazard. The results from other similar subduction zones also favor this model. However, we cannot rule out an alternative model that requires slow slip to invade the seismogenic zone as well. A definitive answer to this critical issue would require more GPS stations and long-term monitoring.

Article

GPS BRECHA SÍSMICA DE GUERRERO TERREMOTOS North America GUERRERO SEISMIC GAP GPS Earthquake concept8601 Seismology CIENCIAS FÍSICO MATEMÁTICAS Y CIENCIAS DE LA TIERRA CIENCIAS DE LA TIERRA Y DEL ESPACIO GEOFÍSICA SISMOLOGÍA Y PROSPECCIÓN SÍSMICA

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 = λi log Ai + µi are derived from Mexican earthquakes. Due to insufficient data, λi has been fixed to 1. Events have been grouped broadly as interplate and intraplate events. Within the range of their validity (7.0≤ M ≤8.2 for interplate; 6.4 ≤ M ≤ 7.1 for intraplate) the relations would give estimate of M to within ± 0.3 to ± 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 ± 22 km.

Article

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

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.

Article

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.

Article

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.

Article

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

Estimation of ground motion in Mexico City from a repeat of the m ~ 7:0 acambay earthquake of 1912

Shri Krishna Singh (2011)

The Acambay earthquake of 1912 (M ~ 7:0), which occurred in the central Trans-Mexican Volcanic Belt (CTMVB) about 100 km west-northwest of Mexico City, has been thought to be a critical scenario event in the estimation of seismic hazard of the city.We use seismograms of two small earthquakes located near Actopan (15 December 2003; 18 May 2010) and recorded at station CUIG, a hill-zone site in Mexico City, as empirical Green's functions (EGFs) for the Acambay region. Because Actopan, like Acambay, is situated in the CTMVB and both are located at about the same distance from CUIG, the use of the recordings of the Actopan earthquakes as EGFs is partly justified. We first analyze data of the two small earthquakes at a local station, DHIG, to estimate their seismic moment and stress drop. As there is considerable uncertainty in the estimated stress drops of the two events, we choose a reasonable range of values for them and apply a technique of random summation of EGFs to simulate ground motion at CUIG from a postulated Mw 7 earthquake. The estimated geometric mean horizontal peak ground acceleration (PGA) and peak ground velocity (PGV) at CUIG range from 2.7 to 9:7 cm=s2 and from 1.1 to 3:0 cm=s, respectively. Ground-motion maps for the entire city are presented using a simulated trace at CUIG and the known transfer functions of many sites within the city. The results are consistent with reported seismic intensities in Mexico City, and PGA and peak ground displacement (PGD) at a 2-s period at the seismic station of Tacubaya during the Acambay earthquake. Estimated ground motions suggest that a repeat of the event does not present significant hazard to Mexico City.

Article

CINTURION VOLCÁNICO TERREMOTO POCO PROFUNDOS EXTENSIÓN MAGNITUD OLAS ATENUACIÓN PREDICCIÓN GRABEN Waves Attenuation Shallow CIENCIAS FÍSICO MATEMÁTICAS Y CIENCIAS DE LA TIERRA CIENCIAS DE LA TIERRA Y DEL ESPACIO GEOFÍSICA SISMOLOGÍA Y PROSPECCIÓN SÍSMICA concept8601 Seismology