Seismological Research Letters, vol. 80, n°6, pp. 977-984, 2009International audienceWe report results from a six-month seismological experiment in the area of the eastern Polochic-Motagua fault system (Guatemala) designed to both characterize the present seismicity and bring some constraints on the lithospheric structure. The seismic activity occurs in the upper 15 km of the crust, on the Polochic and the Motagua faults as well as in a NS-trending graben south of the Motagua fault and within the active folds north of the Polochic fault. From receiver function analysis the Moho discontinuity is found at about 35 km depth north of the Polochic fault and south of the Motagua fault, while the region in between is characterized by a 4-to-6-km thinner crust or by a 6–7% decrease of the Vp/Vs ratio

In many applications, including analysis of seismic signals, Daubechies wavelets perform much better than other families of wavelets. In this paper, we provide a possible theoretical explanation for the empirical success of Daubechies wavelets. Specifically, we show that these wavelets are optimal with respect to any optimality criterion that satisfies the natural properties of scale- and shift-invariance.

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Earthquakes can lead to a huge damage-and the big problem is that they are very difficult to predict. To be more precise, it is very difficult to predict the time of a future earthquake. However, we can estimate which earthquake locations are probable. In general, earthquakes are mostly concentrated around the corresponding faults. For some faults, all the earthquakes occur in a narrow vicinity of the fault, while for other faults, areas more distant from the fault are risky as well. To properly estimate the earthquake's risk, it is important to understand when this risk is limited to a narrow vicinity of a fault and when it not thus limited. This problem has been thoroughly studied for the most well-studied fault in the world: San Andreas fault. This fault consists of somewhat different Northern and Southern parts. The Northern part is close to a straight line, and in this part, earthquake are mostly limited to a narrow vicinity of this line. In contrast, the Southern part is different: it is curved, and earthquakes can happen much further from the main fault. In this paper, we provide a general general explanation for this phenomenon. The existence of such a general explanations makes us expect that the same phenomenon will be observed at other not-so-well-studied faults as well.

In September 2017, over 450 lives were lost in Mexico as a result of two unusual, large-magnitude, normal earthquakes. On 7 September, an M 8.2 earthquake occurred offshore of the State of Oaxaca in the Gulf of Tehuantepec, one of the largest extensional earthquakes to have occurred in a subduction zone. Twelve days later on 19 September an M 7.1 damaging earthquake struck near Puebla and Morelos, over 600 km away. Both earthquakes occurred in the downgoing Cocos plate, which is subducting beneath the North American plate. The first large event was followed on 23 September by a shallow M 6.1 extensional earthquake near Juchitán de Zaragoza, Oaxaca. Researchers from Mexico and the United States collaborated to deploy a temporary seismic network to study the aftershocks of the M 8.2 Tehuantepec, Mexico, earthquake, which included a three-week deployment of 51 Magseis Fairfield Z-Land 5-Hz three-component nodal seismometers (“nodes”) near Juchitán and a 6-month deployment of 10 Nanometrics Trillium 120PA broadband seismometers with Reftek RT130 dataloggers for 6 months. In this article, we analyze the capabilities of the nodes to calculate the horizontal/vertical (H/V) spectral ratio and relative amplification using both microtremors and earthquakes and validate the results calculated with the nodes using data from broadband stations from this and previous deployments in the area. We create maps showing a correlation of the distribution of the fundamental frequency and relative amplification of the soil and compare them with the geology and the damage caused by the September 2017 earthquakes. There is a lack of public awareness and discrepancies in the construction procedures in the region, and we find that the majority of damaged houses in the area of study followed the location of river beds and tended to be in places with low resonance frequencies despite being in a low amplification zone.