Geology topics

Research about Mexico City

Source-linked reports with geographic coverage including Mexico City.

2 recordsLinked to original sources

USGS2022

Zoning Verification in Mexico City Using Strong Motions of the M7.1 Puebla-Morelos Earthquake of September 19, 2017

Mexico City suffers extensive damage from large earthquakes that originate at far distances due mainly to densely built areas on a filled lakebed. Seismic design codes in Mexico recognize the site-specific issues in Mexico City by acknowledging zones that represent lakebed as being riskier compared to other Mexico City areas. At the time of the 19 September 1985 M8.1 Michoacán Earthquake, (a) the seismic zoning map comprised only three zones (Hills [now Zone I], Transition [now Zone II] and Lake Zone [now Zone III] and (b) a limited number of permanent strong motion stations (~6) existed. Since, 1985 the seismic zonation maps have evolved: (a) the Lake Zone (now Zone III) into 4 sub-zones (a, b, c and d) and (b) the number of strong motion stations has increased significantly (~25) and recorded the 19 September 2017 M7.1 Puebla-Morelos earthquake. To identify the site frequency [f] (period [T]) at the specific location of a strong motion station within a particular zone or sub-zone (Zone I, II and III a,b,c,d), two well-known methods (H/H and H/V) for determining spectral ratios are employed using these records. The predominant site periods identified by both methods are in good agreement with those interpolated from the zoning-site period maps of Mexico City in the 2004 Seismic Design Code. Such verification is a testament to the benefits of improved zoning and greater distribution of strong motion network stations, and sets a good example for applications in other seismic regions.

Mexico City↗

USGS2018

The 19 September 2017 M 7.1 Puebla‐Morelos earthquake: Spectral ratios confirm Mexico City zoning

One important element of understanding basin response to strong shaking is the analysis of spectral ratios, which may provide information about the dominant frequency of ground motion at specific locations. Spectral ratios computed from accelerations recorded by strong‐motion stations in Mexico City during the mainshock of the 19 September 2017 M "> M M 7.1 Puebla‐Morelos earthquake reveal predominate periods consistent with those mapped in the 2004 Mexican seismic design code. Furthermore, the predominant periods thus computed validate those studies using mainshock and aftershock recordings of the handful strong‐motion stations that recorded the 19 September 1985 M "> M M 8.1 Michoacán earthquake. Even though the number of stations in each of the zones (zones I, II, IIIa, b, c, and d) is not the same, they still allow confirmation of site frequencies (periods) attributable to the specific zones (particularly those in zones IIIa, b, c, and d). Spectral ratios are computed with two different methods: (1) horizontal to horizontal (H/H) ratio of smoothed amplitude spectrum of a horizontal channel in direction X of a station with respect to the smoothed amplitude spectrum of the horizontal channel in the same X direction of a reference stiff soil (or rock) station and (2) horizontal to vertical (H/V) ratio (or also known as the Nakamura method) of both horizontal (H) and vertical (V) channels of the same station. We show a comparison of the identified frequencies (periods) derived by both methods and find they are very similar and in good agreement with those indicated in the zoning maps of Mexico City in the 2004 seismic design code.

Mexico City↗