Damages observed in locations of Oaxaca due to the Tehuantepec Mw8.2 earthquake,Mexico

On September 7, 2017, at 23:49 h (local time), a Mw8.2 intermediate-depth normal-fault earthquake occurred in the Gulf of Tehuantepec, 133 km away from Pijijiapan, Chiapas, and about 700 km away from Mexico City. This event caused 95 fatalities and severe damage to different types of structures located close to the epicenter. The main objective of this work is to present observed damages caused in the state of Oaxaca by this earthquake, which were mainly concentrated in self-built houses and historical and ancient buildings. The locations visited by the reconnaissance team of the Institute of Engineering from UNAM in Oaxaca included Salina Cruz, Tehuantepec, Ixtaltepec, Juchitán, Huatulco and La Ventosa.

     

Orientation effect on ground motion measurement for Mexican subduction earthquakes

The existence of the principal directions of the ground motion based on Arias intensity is well-known. These principal directions do not necessarily coincide with the orientations of recording sensors or with the orientations along which the ground motion parameters such as the peak ground acceleration and the pseudo-spectral acceleration (PSA) are maximum. This is evidenced by the fact that the maximum PSA at different natural vibration periods for horizontal excitations do not correspond to the same orientation. A recent analysis carried out for California earthquake records suggests that an orientation-dependent ground motion measurement for horizontal excitations can be developed. The main objective of this study is to investigate and provide seismic ground motion measurements in the horizontal plane, including bidirectional horizontal ground motions, for Mexican interplate and inslab earthquake records. Extensive statistical analyses of PSA are conducted for the assessment, The analysis results suggest that similar to the case of California records, the average behavior of the ratio of the PSA to the maximum resulting PSA can be approximated by a quarter of an ellipse in one quadrant; and that the ratio can be considered to be independent of the value of the maximum resulting PSA, earthquake magnitude, earthquake distance and the focal depth. Sets of response ratios and attenuation relationships that can be used to represent a bidirectional horizontal ground motion measurement for Mexican interplate and inslab earthquakes were also developed.     

Effects of hurricane Odile on the infrastructure of Baja California Sur,Mexico

In September 2014, the state of Baja California Sur (BCS), Mexico, was struck by hurricane Odile. The hurricane caused extensive damage to the infrastructure of the state of BCS, where the energy and water supply were interrupted for several days. The direct economic impact was estimated to be more than 1654 million USD. Considering this damage, few days after the cyclonic event, a technical visit to BCS was carried out. The objective of this study is to present the relevant information on the performance of the infrastructure observed after the event, and to make recommendations in order to mitigate the effects of future cyclonic storms in Mexico, based on the observations during the technical visit. The main causes of damage were the use of materials for non-structural elements with a weak performance under high wind speeds, failures in the design and construction of connections of structural and non-structural elements, accumulated damage, lack of maintenance and impact of wind-born debris, as well as the absence of a building code in the region. Background information about meteorological and climatological aspects of the cyclones that have affected the southern region of BCS, the characteristics of hurricane Odile, the analysis of structural damages and the conclusions, are also presented.