HIGH PRECISION MEASUREMENTS OF ABSOLUTE GRAVITY IN MEXICO: THE JALISCO BLOCK CHANGES IN GRAVITY TRIGGERED BY DISTANT EARTHQUAKES
Por:
Esparza, Alfredo, Arzate, Jorge, Timmen, Ludger, Silliker, Jason, Schilling, Manuel
Publicada:
1 jul 2020
Resumen:
We report the results of 16 Absolute Gravity (AG) measurements
distributed central and western Mexico employing two free-fall gravity
instruments; the FG5X-220 of Leibniz Universitat Hannover (LUH), and the
FG5X-252 instrument of the Centro Nacional de Metrologia (CENAM).
Previous to the setup of new stations and acquisition campaigns, the
FG5X-252 was certified in two steps, first a mutual comparison with the
reference gravimeter FG5X-220, which have a long range stability below 2
uGal, and later through an international comparison at NOAA's Table
Mountain, Col. facilities with 13 other instruments of different
countries.
The acquisition campaigns in the Jalisco Block (JB) took place during
the dry season of 2016 and 2018, which included AG stations in Chamela
(CHA), Guadalajara (AGG), Manzanillo (MAN), Puerto Vallarta (UGP), and
Tepic (TEP); the later established new reference station in the north of
the JB in 2016. The results obtained from the 2016 and 2018 field
campaigns in the JB were compared with 1996 AG data acquired by NOAA at
the same sites established. The observed vertical displacements in the
two years period at stations CHA (+22.7 cm), UGG (+44.3 cm) and MAN
(+54.6 cm) overcomes substantially the annual average (2.8 cm, 4.2 cm y
3.6 cm respectively) from the difference of the AG measurements
2016-1996. In the same period the UGP station subsided 8.5 cm, while
station TEP remained quite stable (-0.25).
In September 2017 two large earthquakes of magnitudes 8.2 and 7.1
occurred in the coast of Chiapas (07/Nov/2017) and in the State of
Puebla (19/Nov/2017), which were recorded at some of the UNAVCO `s GPS
stations, namely MAN, UGG and CHA even though the nearest seismic source
was located more than 500 km to the east. The analysis of our results in
combination with other geophysical data support the hypothesis that the
earthquake with epicenter in Puebla triggered the aseismic subduction of
a segment of the Ribera Plate (RP), which in turn uplifted the stations
above mentioned. We conclude that the aseismic subduction in this region
is facilitated by a wet oceanic crust that carries important amounts of
marine sediments, producing a lubricated interface between oceanic RP
and the overriding JP.
Filiaciones:
Ctr Nacl Metrol CENAM, Km 4-5 Carretera Los Cuis, El Marques 76246, Qro, Mexico
Posgrad Ciencias Tierra, Campus UNAM Juriquilla,Blvd Juriquilla 3001, Queretaro 76230, Mexico
Ctr Geociencias, Campus UNAM Juriquilla,Blvd Juriquilla 3001, Queretaro 76230, Mexico
Leibniz Univ Hannover LUH, Schneiderberg 50, D-30167 Hannover, Germany
Nat Resources Canada NRC RNCan, Ottawa, ON, Canada
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