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Geometry transition in the Cocos plate, from flat-steep to constant dip
ABSTRACTSubduction of the Cocos plate beneath North America has a variable and complex behavior along the Middle-American Trench. Initially, its geometry was delineated from regional seismicity. In the last 10 years, seismic experiments have illuminated some details in the geometry. They have reported, from NW to SE an abrupt dip transition, from 50 to 26°, as the result of a tear that splits Cocos North from Cocos South; then there is a smooth transition to a horizontal geometry under central Mexico. Further southeast, under the Isthmus of Tehuantepec, the Cocos plate shows a constant ~26° subduction dip. This last transition has been assumed to be smooth from the sparse seismicity in the region. A first glimpse of the slab geometry under Oaxaca, shows the slab continues to be flat at least until 97.5°W longitude, where the slab suddenly changes to a ~55° dip to the northeast. This occurs at a distance of ~75 km from the Pico de Orizaba volcano, which is a similar distance as the active Popocatepetl volcano from the place where the slab dives into the mantle along the Meso-American Subduction Experiment line, in central Mexico. East of this region, receiver function images show an abrupt change in the geometry and length of the slab.
Xyoli Pérez-Campos1, Robert W. Clayton2, Miguel A. Rodríguez3, Michael R. Brudzinski4, Carlos Valdés-González1, Enrique Cabral1, Alejandra Arciniega1, Francisco Córdoba-Montiel5
1 Instituto de Geofísica, Universid Nacional Autónoma de México. xyoli@geofisica.unam.mx2 Seismological Laboratory, California Institute of Technology
3 Posgrado en Ciencias de la Tierra, Universidad Nacional Autónoma de México4 Department of Geology and Environmental Earth Science, Miami University
5Centro de Ciencias de la Tierra, Universidad Veracruzana.MASE VEOX
Easter Transision
112
-105˚
-105˚
-100˚
-100˚
-95˚
-95˚
-90˚
-90˚
15˚ 15˚
18˚ 18˚
21˚ 21˚MCVA
LTVF
AH
TMVB
20 km
40 km
60 km
80 km
100 km
150 km
Slab edge
PACIFIC
MAT
OGFZ
OFZ
TR
NORTH AMERICA
COCOS
RIVERA
CARIBBEAN
RFZ
EPR
11,4.8
17.6,5.6
8,2.0
17.5,6.314.5,5.6
18,6.3
23,7.1
35,7.1
10,2.4
432
1
SSN
OXNETCENAPREDVEOXMASEMARS
UV
Stations
20132013-2015
Slab contours modified fromPardo & Suárez (1995)
2.5
2.0
1.5
1.0
0.5
0.0
-0.5
-1.0
Dep
th [k
m]
Horizontal distance from Acapulco station [km]
Tom
ogra
phy:
% d
iffer
ence
to th
e ba
ckgr
ound
mod
el
-1.0 -0.8 -0.6 -0.4 -0.2 0.0 0.2 0.4 0.6 0.8 1.0
RF: Average Amplitude
LVM (NA)Continental crust (NA Plate)LC (NA)
Mantle wedge
OC (C Plate)
0 100 200 300 400 500
100
200
300
400
500
600
700 700
600
500
400
300
200
100
0
Aca
pulc
o
Mex
ico
City
Tem
poal
TMVB2 20E
leva
tion
[km
]
Horizontal subduction for ~200 km.LVL.
Pérez-Campos et al. (2008)Husker & Davis (2009)Kim et al. (2010; 2012)
MASEMASE
Steep subduction of 76°.Slab reaches 500 km depth.
REFERENCES:Espíndola Castro, V.H. (2009). Ph.D. Thesis, Posgrado en Ciencias de la Tierra, UNAM, 120 pp.
Husker, A. & Davis, P.M. (2009). J. Geophys. Res., 114, B04306, doi:10.1029/2008JB006039.
Kim, Y., Clayton, R.W. & Jackson, J.M. (2010). J. Geophys. Res., 115, B06310, doi:10.1029/2009JB006942.
Kim, Y., Miller, M.S, Pearce, F. & Clayton, R.W. (2012). Geophys. Geosyst., 13, Q07001, doi:10.1029/2012GC004033.
Melgar, D. & X. Pérez Campos (2011). Pure Appl. Geophys., DOI 10.1007/s00024-010-0199-5.
Pardo, M. & Suárez, G. (1995). J. Geophys. Res., 110, B7, 12,357-
Pérez-Campos,X., Kim, Y., Husker, A., Davis, P.M., Clayton, R.W., Iglesias, A., Pacheco, J.F., Singh, S.K., Manea, V.C. & Gurnis, M. (2008).
Geophys. Res. Lett., 35, L18303, doi:10.1029/2008GL035127.
Rodríguez Domínguez, M. (2013). Bachelor's Thesis, Facultad de Ingeniería, UNAM, 68 pp.
Slab dip: 26°.No plate is observed beyond 150 km depth.
VEOXVEOX
Melgar & Pérez-Campos (2011)
SSN localized hypocenters
Cocos Plate (PARDO and SUÁREZ, 1995)Cocos Plate, this studyMoho, this study
Relocated events (CASTRO ARTOLA, 2010)
PacificOcean
Gulf ofMexico
MAT
LTVFCoast
A A’
1000
2000
1000
2000
1000
2000Elevation [m]
Distance from trench [km]
Dep
th [k
m]
0
25
50
75
100
125
150
175
200
225
250
0
25
50
75
100
125
150
175
200
225
2500 50 100 150 200 250 300 350 400 450
GECOGECO
Smooth geometry transition was inferred from scarse seismicity (Pardo & Suárez, 1995).Slab depth at SSN (Espíndola Castro, 2009) and TUXT stations (Rodríguez Domínguez, 2013), suggests otherwise.
GECO: Geometry of Cocos
50
100
150
200
450 0 50 100 150 200 250 300 350 400 450
50
100
150
200
250
Distance along profile [km]
NECoa
st
Coa
stProfile 4
450 0 50 100 150 200 250 300 350 400
Coa
st
Coa
stProfile 3
0 50 100 150 200 250 300 350 400
Profile 2
50
100
150
200
250
Dep
th [k
m]
−50 0 50 100 150 200 250 300 350 400 450
0
50
100
150
200
250
0
Dep
th [k
m]
SW Coa
st Profile 1
Average Amplitude
−1.0 −0.6 −0.2 0.2 0.6 −1.0
TMVB = Trans Mexican Volcanic BeltAH = Anegada HighLTVF = Los Tuxtlas Volcanic FieldMCVB = Modern Chiapanecan Volcanic Belt
EPR = East Pacific RiseMAT = Middle American TrenchRFZ = Rivera Fracture ZoneOFZ = Orozco Fracture ZoneOGFZ = O‘Gorman Fracture ZoneTR = Tehuantepec Ridge
Age,Convergence rate11,4.8
km
TUXT?
Top right: Backprojected RF profiles (top) and interpreted profiles (bottom). Dots are hypocenters reported in the SSN catalogue. Gray lines correspond to Pardo & Suárez (1995) top of the slab. Brown line shows Moho; blue and red lines, top and bottom of the oceanic crust, as interpreted from RFs. Light blue and light orange lines show alternative RF interpretation. Profiles 1 and 2 show a horizontal subduction, consistent with Pardo & Suárez (1995) and seismicity. Profiles 3 and 4, show two possibilities, one is somewhat consistent with Pardo & Suárez (1995), and the other one shows a deeper slab. This might be due to azimuthal variation, suggesting the geometry transition taking place in this region is not smooth.
Coa
st
Seismicity and receiver functions delineate the geometry of the slab, going from horizontal subduction in central Mexico to central Oaxaca, and changing abruptly to the east for a smooth 26° dip angle. This suggest a possible tear in the slab.
Conclusions and future work
17 portable stations are to be installed in the area (light blue
squares), plus 3 permanent statios (green squares) to
focus on the deeper transition.−99˚
−99˚
−98˚
−98˚
−97˚
−97˚
−96˚
−96˚
−95˚
−95˚
−94˚
−94˚
14˚ 14˚
15˚ 15˚
16˚ 16˚
17˚ 17˚
18˚ 18˚
19˚ 19˚
20˚ 20˚
21˚ 21˚
TR
43
21
MAT
Our gratitude to station operatos of SSN, GECO
and OXNET. Stations currently operating in
Oaxaca are funded through PAPIIT-UNAM
project IN119505-3, stations in Veracruz and Puebla trough Conacyt
project 177676
Acknowledgements
Bottom left: Slab isodepth contours. Dotted lines are isodepth contours from Pardo & Suárez (1995). Continuous lines are interpolated contours given slab depths observed by Espíndola Castro (2009) at SSN stations (large squares), by Melgar & Pérez-Campos along the VEOX profile (small squares), and by Rodríguez Domínguez (2013) at station TUXT (circles).
Rodríguez Domínguez (2013)
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