The Oaxaca, Mexico, earthquake of 1931: lithospheric normal faulting in the subducted Cocos plate

Nature ◽  
1985 ◽  
Vol 317 (6032) ◽  
pp. 56-58 ◽  
Author(s):  
S. K. Singh ◽  
Gerardo Suárez ◽  
T. Domínguez
Keyword(s):  
Normal Faulting ◽  
Cocos Plate ◽  
Mexico Earthquake

scholarly journals A possible stress interaction between large thrust and normal faulting earthquakes in the Mexican subduction zone

1999 ◽  
Vol 89 (6) ◽  
pp. 1418-1427 ◽  
Author(s):  
Takeshi Mikumo ◽  
Shri Krishna Singh ◽  
Miguel A. Santoyo
Keyword(s):  
High Stress ◽  
Stress Change ◽  
Vertical Shear ◽  
3D Analysis ◽  
Normal Faulting ◽  
Dynamic Rupture ◽  
Cocos Plate ◽  
Stress Changes ◽  
Subducting Plate ◽  
Mexico Earthquake

Abstract A large, nearly vertical, normal-faulting earthquake (Mw = 7.1) took place in 1997 in the subducting Cocos plate just beneath the ruptured fault zone of the 1985 Michoacan, Mexico, earthquake (Mw = 8.1). We investigate the possibility of stress interaction between the two large events through a 3D analysis of coseismic-stress change that was due to the first event, taking into consideration the postseismic change and the dynamic rupture process of the second event. In the middle portion of the subducting plate at depths below 30 km, the calculated coseismic increase in the vertical-shear stress and in the Coulomb-failure stress beneath the high stress-drop zones of the 1985 earthquake is in the order of 0.4 to 0.8 MPa. It was also found that the 1997 earthquake took place in the zone of maximum coseismic-stress increase. Possible postseismic-stress changes due to the subduction process or to the loading of the overriding continental lithosphere and from aseismic slip would enhance the coseismic-stress change and hence the possibility of occurrence of a normal-faulting earthquake in the subducting plate. The dynamic rupture pattern of the 1997 event seems to be consistent with the inferred stress interactions.

The great Mexican earthquake of 19 June 1858: Expected ground motions and damage in Mexico City from a similar future event

1996 ◽  
Vol 86 (6) ◽  
pp. 1655-1666 ◽  
Author(s):  
S. K. Singh ◽  
M. Ordaz ◽  
L. E. Pérez-Rocha
Keyword(s):  
Mexico City ◽  
Transfer Functions ◽  
Ground Motions ◽  
Careful Examination ◽  
Great Earthquake ◽  
Normal Faulting ◽  
Cocos Plate ◽  
Current Design ◽  
Peak Horizontal Acceleration ◽  
The City

Abstract The description of the great earthquake of 19 June 1858 is unusual: damage and high intensities were reported both in the state of Michoacan and in Mexico City. Although a coastal epicenter for this earthquake cannot be ruled out, the reports agree better with an intermediate-depth (about 50 km), normal-faulting event in the subducted Cocos plate. A careful examination of the reports of this event and other normal-faulting events below the Mexican altiplano suggests that a likely location is 18.0 °N, 100.8 °W, near the epicenter of the 6 June 1964 (M7.3, H = 55 km) event. This location is 220 km SW of the city. The magnitude of the earthquake is estimated to be about 7.7. We synthesize expected ground motions in CU, a hill-zone site in the city, from an event similar to that of 1858, using records from the 23 May 1994 earthquake (18.0 °N, 100.6 °W, H = 50 km, M5.7) as an empirical Green's function and stress parameter, Δσ, of 50, 160, and 300 bar. The expected peak horizontal acceleration in CU of Δσ = 160 bar is about 30 gals. Similar acceleration was recorded in CU during the 1985, Michoacan earthquake (M8.0). We compute expected ground motions at many sites in Mexico City using empirical transfer functions and random vibration theory and compare these motions and the expected damage in the city with those from the 1985 Michoacan earthquake. Results show that the overall expected damage during the postulated earthquake is ⅔ and 1⅓ of that during the Michoacan earthquake for Δσ = 160 and 300 bar, respectively. A greater percentage of low-rise construction, which constitute about 80% of the total in the city, will be damaged during the postulated earthquake than during the Michoacan earthquake. The expected ground motions for Δσ = 50 bar are smaller at all periods than those from the Michoacan earthquake. As the present building code for Mexico City contemplates coastal earthquakes of magnitude greater than 8.0, the case of Δσ = 50 bar is not of interest in this article. This preliminary study suggests a need for a more careful evaluation of expected ground motion in the Valley of Mexico from the postulated earthquake and its impact on the current design spectra of the city.

The Mw7.1 September 19th Puebla-Morelos (Mexico) earthquake triggered by brucite and antigorite dewatering

2021 ◽  
Author(s):  
Fabián Gutiérrez-Aguilar ◽  
David Hernández-Uribe ◽  
Robert M. Holder ◽  
Cailey B. Condit
Keyword(s):  
Fluid Pressure ◽  
Convergent Margins ◽  
Cocos Plate ◽  
Outer Rise ◽  
Geological Processes ◽  
Bending Stresses ◽  
Positive Volume ◽  
Flat Portion ◽  
Mexico Earthquake ◽  
Ocean Ridge

<p>Subduction controls key geological processes at convergent margins including seismicity and resultant seismic hazard. The September 19th 2017 Mw7.1 Mexican earthquake nucleated ~250 km from the trench within the Cocos plate near its Moho, ~57 km below Earth’s surface. The prevailing hypothesis suggests that this earthquake resulted from bending stresses occurring at the flat-to-steep subduction transition. Here, we present an alternative, but not mutually exclusive, hypothesis: the dehydration reaction brucite + antigorite = olivine + H2O in the slab mantle controls intermediate-depth seismicity along the flat portion of the subducted Cocos plate. This reaction releases a substantial amount of H2O, resulting in a large positive volume change, and thus in an increase in pore fluid pressure at the appropriate depth–temperature conditions to cause the Puebla-Morelos and other intraslab earthquakes in Mexico. The amount of H2O released by this reaction depends on the degree of serpentinization of the oceanic mantle prior to subduction. Only oceanic mantle with > 60% serpentinization—as expected along abundant deep extensional faults at the mid-ocean-ridge or where the plate bends at the outer rise—will stabilize brucite, and thus, will experience this reaction at the same depths where the September 19th 2017 earthquake nucleated.</p>

The Oaxaca Earthquake of 30 September 1999 (Mw = 7.5): A Normal-faulting Event in the Subducted Cocos Plate

2000 ◽  
Vol 71 (1) ◽  
pp. 67-78 ◽  
Author(s):  
S. K. Singh ◽  
M. Ordaz ◽  
L. Alcantara ◽  
N. Shapiro ◽  
V. Kostoglodov ◽  
...  
Keyword(s):  
Normal Faulting ◽  
Cocos Plate

Estimation of Ground Motions in the Valley of Mexico from Normal-Faulting, Intermediate-Depth Earthquakes in the Subducted Cocos Plate

1995 ◽  
Vol 11 (2) ◽  
pp. 233-247 ◽  
Author(s):  
Javier F. Pacheco ◽  
Shri Krishna Singh
Keyword(s):  
Seismic Waves ◽  
Ground Motions ◽  
Seismic Source ◽  
Source Model ◽  
Normal Faulting ◽  
Cocos Plate ◽  
Intermediate Depth ◽  
S Waves ◽  
Local Site ◽  
Seismic Source Model

The Valley of Mexico is exposed to seismic risk from normal-faulting, large intermediate-depth earthquakes. We explore two approaches to estimate future ground motions from such events at CU, a hill-zone site in the valley. In the first we obtain parameters of an ω2 seismic source model and determine amplification of seismic waves due to local site effects at CU. This permits estimation of Fourier spectrum of expected ground motion at CU from postulated earthquakes. We find that the S-waves suffer an amplification of 2.5 between 0.2 to 3.0 Hz. This amplification is similar to that observed from deep teleseismic events but differs from that obtained from shallow coastal events. In the second approach the available recordings at CU are used as empirical Green's functions (EGF) to synthesize motions from future large earthquakes. This approach is very powerful if the smaller event is truly an empirical Green's function for the postulated earthquake.

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