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Since the eighties, several subduction earthquakes on the Mexican Pacific coast have been recorded at accelerometric networks in the Valley of Mexico (VM). Such are the cases of the 19 September 1985 M 8.1 Michoacán earthquake and the recent 7 September 2021 M 7.1 Guerrero earthquake. These events have caused from minor damages to widespread structural collapses in the VM. The vertical ground motion recorded at several sites in the VM clearly show recurrent Rayleigh wavetrains, which present similar characteristics in period, amplitude, and duration among stations. These characteristics are very stable in space and time. On the other hand, the corresponding horizontal ground motion are strongly affected by the surface geology of the valley because of the shear wave-energy trapped at the uppermost soft layers. In addition, the horizontal response at several soft-ground sites displays significant azimuthal effects. Based on these observations, we analyze thrust-faulting subduction earthquakes that occurred along the Mexican Pacific coast from Michoacán to Chiapas states, all recorded at the VM accelerometric networks. We identified similarities in the vertical and horizontal ground motion not only among stations but also between seismic events recorded at the same station. The local generation of surface waves is studied using a kinematic analysis in the frequency-wavenumber domain (f-k), and sundry techniques in frequency and time domains. As a preliminary explanation, our analysis suggests that azimuthal effects related to thrust faulting subduction earthquakes strongly influence the local generation of surface waves affecting the 3D response of the valley. Moreover, for all earthquakes in all stations, our results show that while the vertical ground motion is similar and its amplifications are small and governed by earthquake size, the two horizontal components reveal strong site effects. [ABSTRACT FROM AUTHOR]

The article discusses a workshop on scientific drilling project at Lake Basin in Mexico sponsored by the International Continental Scientific Drilling Program (ICDP) which funds geology projects and Universidad Nacional Autónoma de México from 4-8 March, 2012 in Mexico City, Mexico. The project main aim was evaluation of climate and ecological record preserved in the lake sediments. The workshop featured participants with specialization in borehole instrumentation technology.

We describe three unique types of seismicity at Popocatépetl volcano that accompanied the initial vent-clearing eruptive activity in December 1994 through the eruption of the first two domes in 1996. We identify and describe two types of coupled events, 1) spasmodic burst coupled events, a burst of volcano tectonic (VT) events coupled with a large eruptive explosion (21 December 1994 and 5 March 1996), and 2) explosion-couplet coupled events, a pair of events with a deeper first event and whose second event correlates with a small gas emission or explosion. Explosion-couplets occurred with the onset of magmatic ash dominated eruptions and their properties are very useful for forecasting magmatic eruptions at Popocatépetl volcano. Measurable quantities including the time between the first and second phase, daily numbers of events, and the amplitude ratio between the second and first phase systematically changed as the first two domes approached the surface between March and June 1996. Interevent times decreased from many tens of seconds to a few seconds, while amplitude ratios increased from about 2 to 10 or more. Event numbers increased prior to and during initial dome extrusion. These changes were used to forecast the eruption of the first two domes. We also report on another unusual type of low frequency seismicity that accompanied emissions called fluidized bed events. Fluidized bed events occurred following the initial eruption on 21 December 1994, beginning mid-January 1995, when SO 2 emissions were initially elevated, and the conduit was open. Fluidized bed events began to wane in late March through the end of May 1995 as did SO 2 emissions. Consistent gas, visual and seismic observations by Centro Nacional de Prevención de Desastres (CENAPRED) enabled the direct correlation of the gas, magma, and seismic phenomena. • A spasmodic burst coupled event comprised the first eruption in December 1994. • Fluidized bed events dominated for several months following the first eruption. • A pair of coupled events comprised the second eruption in March 1996. • Explosion-couplet interevent times decreased prior to dome extrusions in 1996. • Amplitude ratios of explosion-couplets increased prior to dome extrusions in 1996. [ABSTRACT FROM AUTHOR]