Reduced vertical gravity gradient shows a good correlation with rupture structure for certain degrees of the harmonic expansion and related depth of the causative mass; indicating, such
Trang 1Rupture area analysis of the Ecuador (Musine) Mw ¼ 7.8 thrust
earthquake on April 16, 2016, using GOCE derived gradients
Q4 Orlando Alvarez a,b,* , Andres Folguera c , Mario Gimenez a,b
aInstituto Geofísico y Sismologico Ing, Volponi, Universidad Nacional de San Juan, Argentina
Q1
bConsejo Nacional de Investigaciones Científicas y Tecnicas, Argentina
cINDEANe Instituto de Estudios Andinos “Don Pablo Groeber”, Departamento de Cs Geologicas, FCEN, Universidad de Buenos Aires, Argentina
a r t i c l e i n f o
Article history:
Received 4 July 2016
Received in revised form
30 December 2016
Accepted 19 January 2017
Available online xxx
Keywords:
Gravityfield and Ocean Circulation Explorer
(GOCE)
Vertical gravity gradient
Ecuador earthquake
Trench sediments
Rupture zone
a b s t r a c t The Ecuador Mw¼ 7.8 earthquake on April 16, 2016, ruptured a nearly 200 km long zone along the plate interface between Nazca and South American plates which is coincident with a seismic gap since
1942, when a Mw¼ 7.8 earthquake happened This earthquake occurred at a margin characterized by moderately big to giant earthquakes such as the 1906 (Mw¼ 8.8) A heavily sedimented trench explains the abnormal lengths of the rupture zones in this system as inhibits the role of natural barriers on the propagation of rupture zones High amount of sediment thickness is associated with tropical climates, high erosion rates and eastward Pacific dominant winds that provoke orographic rainfalls over the Pacific slope of the Ecuatorian Andes Offshore sediment dispersion off the oceanic trench is controlled
by a close arrangement of two aseismic ridges that hit the Costa Rica and South Ecuador margin respectively and a mid ocean ridge that separates the Cocos and Nazca plate trapping sediments Gravityfield and Ocean Circulation Explorer (GOCE) satellite data are used in this work to test the possible relationship between gravity signal and earthquake rupture structure as well as registered aftershock seismic activity Reduced vertical gravity gradient shows a good correlation with rupture structure for certain degrees of the harmonic expansion and related depth of the causative mass; indicating, such as in other analyzed cases along the subduction margin, that fore-arc structure derived from density heterogeneities explains at a certain extent propagation of the rupture zones In this analysis the rupture zone of the April 2016 Ecuador earthquake developed through a relatively low density zone of the fore-arc sliver Finally, aftershock sequence nucleated around the area of maximum slips in the rupture zone, suggesting that heterogeneous density structure of the fore-arc determined from gravity data could be used in forecasting potential damaged zones associated with big ruptures along the subduction border
© 2017 Institute of Seismology, China Earthquake Administration, etc Production and hosting by Elsevier B.V on behalf of KeAi Communications Co., Ltd This is an open access article under the CC BY-NC-ND
license (http://creativecommons.org/licenses/by-nc-nd/4.0/)
1 Introduction During the last years Gravity field and Ocean Circulation Ex-plorer (GOCE) data [1 e4] have been used successfully to associate fore-arc density structure in subduction zones with internal displacement distribution in large rupture areas associated with thrust subduction earthquakes [5 e8] This association is aimed to constitute a predictive tool in earthquake seismology following a premise in which rupture areas propagate underneath low density zones of the fore-arc after initiating in asperities located over the
* Corresponding author Ruta 12, Km 17, Jardín de los Poetas, Rivadavia, San Juan,
Argentina
E-mail addresses: orlando_a_p@yahoo.com.ar, orlando.alvarez@conicet.gov.ar
(O Alvarez)
Peer review under responsibility of Institute of Seismology, China Earthquake
Administration
Production and Hosting by Elsevier on behalf of KeAi
Contents lists available at ScienceDirect Geodesy and Geodynamics
j o u r n a l h o m e p a g e s : w w w k e a i p u b l i s h i n g c o m / e n / j o u r n a l s / g e o g ;
h t t p : / / w w w j g g 0 9 c o m / j w e b _ d d c l _ e n / E N / v o l u m n / h o m e s h t m l
http://dx.doi.org/10.1016/j.geog.2017.01.005
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
55 56 57 58 59 60 61 62 63 64 65 66 67 68 69 70 71 72 73 74 75 76 77 78 79 80 81 82 83 84 85 86 87 88 89 90 91 92 93 94 95 96 97 98 99 100 101 102 103 104 105 106 107 108 109 110 111 112 113 114 115 116 117 118
Trang 2subducted oceanic floor [9 e13] Then an acceptable to remarkable
match, in some cases, is noticed in some of the major earthquake
subduction phenomena (M > 8) such as the Valdivia (1960),
Are-quipa (2001), Pisco (2007), Maule (2010), Pisagua-Iquique (2014)
and Illapel (2015) large earthquake events with vertical gradient
gravity anomalies of GOCE satellite data [6 e8]
This work is aimed to test such relation in the recent Ecuador
Mw ¼ 7.8 thrust earthquake on April 17, 2016, 28 km SSE of Muisne
( Fig 1 ) For this purpose GOCE data are corrected by either their
topographical as trench-sedimentary effects, isolating crustal
component linked to the heterogeneous density structure of the
fore-arc zone Additionally, vertical gravity gradient from GOCE is
discomposed by cutting-of at different degrees of the spherical
harmonic expansion in order to isolate contributions from mass
heterogeneities at different depths and thus to find a term that
best fit measured displacements into the rupture area and gravity
data.
The Ecuador Mw ¼ 7.8 thrust earthquake on April 16, 2016 has
ruptured an area similar to a rupture zone developed in 1942 with
an earthquake magnitude of Mw ¼ 7.8 at similar latitudes,
sug-gesting that seismic segmentation depends on mechanical
prop-erties of the interplate medium that is affected by co- and
post-seismic displacements However, transform faults associated
with the Cocos-Nazca mid ocean ridge that usually determine
barriers to rupture propagation, dispose parallel to the Ecuador-south Colombia subduction zone The arrangement of the plate interface with respect to the subduction zone, summed to the fact that no aseismic ridge impacts north of the Carnegie aseismic ridge (CR) that could have limited both the 1942 and 2016 rupture propagation zones, suggests that upper plate density structure could be playing a role in earthquake segmentation, as suggested
in previous works for other subduction segments along the Peruvian-Chilean trench [14] Therefore, this work explores den-sity structure of the fore-arc zone and its potential relation to seismic segmentation in the interplate zone through processing of satellite gravity data.
2 Seismotectonic setting The Ecuador Mw ¼ 7.8 thrust earthquake on April 17, 2016 is part of a series of rupture zones that have filled partially a large gap of approximately 500 km ( Fig 2 ) that had not been totally ruptured in one single event since the Mw ¼ 8.8 1906 earthquake.
In 1979 an Mw ¼ 8.2 earthquake ruptured to the North, while the
1958 Mw ¼ 7.7 earthquake [20] filled the central region of this seismic gap In particular, the analyzed 2016 rupture ( Fig 2 ) would constitute a reactivation of the 1942 rupture area of such gap
[20 e23] Ye et al [25] pointed out the similarity of the 1942 and
Fig 1 Ecuador and Colombia subduction zone with indication of the Northern Volcanic zone comprehended between the Perú and Bucaramanga arc gaps and location of the
Mw¼ 7.8 earthquake epicenter on April 17, 2016 (red star) with corresponding focal mechanism Note the high complexity of this subduction segment that involves collision of
the Carnegie aseismic ridge at the Guayaquil Gulf and subduction of a mid ocean ridge separating Nazca and Cocos plates, transversally disposed respect to the trench
Relief is from ETOPO1[15], triangles indicate the current position of the active volcanic arc[16] References: G-Fz: Gijalva Fz, A-Fz: Alvarado Fz, S-Fz: Sarmiento Fz, YG: Yaquina
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
66 67 68 69 70 71 72 73 74 75 76 77 78 79 80 81 82 83 84 85 86 87 88 89 90 91 92 93 94 95 96 97 98 99 100 101 102 103 104 105 106 107 108 109 110 111 112 113 114 115 116 117 118 119 120 121 122 123 124 125 126 127 128
Trang 3Fig 2 Fore-arc sliver detached through the arc zone associated with oblique convergence of the Nazca Plate against South American Plate Seismic structure along the Ecuador-southern Colombia fore-arc zone taken from Ref.[17], DGFZ: DoloreseGuayaquil fault zone[18] Superimposed slip distributions (dashed ellipses) of the main earthquakes: 1906
Mw¼ 8.8; 1942 Mw ¼ 7.8; 1958 Mw ¼ 7.7, 1979 Mw ¼ 8.2 and 2016 Mw ¼ 7.8 Colored stars indicate location of Mw > 7.5 epicenters and dashed ellipses delineate the approximate rupture area with the same color as corresponding epicenter[19e25] Convergence rate is from Ref.[26])
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
66 67 68 69 70 71 72 73 74 75 76 77 78 79 80 81 82 83 84 85 86 87 88 89 90 91 92 93 94 95 96 97 98 99 100 101 102 103 104 105 106 107 108 109 110 111 112 113 114 115 116 117 118 119 120 121 122 123 124 125 126 127 128 129
Trang 42016 events in an observed heterogeneous pattern of interseismic
coupling of the plate interface and rupture of a similar subset of
asperities, which probably also ruptured as part of the 1906 event.
These authors suggested that the seismic asperities are
probably associated with persistent spatial variations of frictional
properties of the megathrust over successive ruptures Chlieh et al.
[17] found a heterogeneous locking of the plate interface by
modeling interseismic geodetic strain Patches with high
inter-seismic coupling are close to the rupture areas of the 1942, 1958
and 1979 earthquakes, supporting the notion of some persistent
segmentation of the plate boundary The inferred rupture of
several asperities beneath the coastline by Ref [25] is consistent
with the patchy interseismic locking pattern and location of the
large slip de ficit patches from Ref [17] The last authors reported
that the characteristic recurrence time for these events is of
575 ± 100 yr (1906), 140 ± 30 yr (1942), 90 ± 20 yr (1958) and
153 ± 80 yr (1979), at the actual long-term moment deficit
accu-mulation rate.
Historical ruptures are limited to the south by the zone of
inception of the Carnegie aseismic ridge into the subduction zone
( Figs 1 and 2 ) since none of these events appears to have
ruptured across the ridge [27] These ruptures developed along a
heavily sedimented trench due to the tropical location of the
northern Ecuador eColombia Andes and Pacific dominant winds
that provoke orographic rains on the western Andean slope and
provoke a strong rain gradient from the Peruvian to the
Ecua-torian western Andean slope Particularly, along the north
Ecuador-south Colombia margin, the trench shows a thick
sedi-mentary in fill (2e3 km) probably due to recent and massive
turbiditic intakes, via canyons, in association with hemipelagic
sedimentation [24,28 e30] This sediment supply fills the trench
and is trapped by an intricate ocean floor morphology constituted
by two nearly perpendicular aseismic ridges ( Fig 1 ) produced
from the Galapagos hot spot and a mid ocean ridge positive
morphology that separates Nazca and Cocos plates [31,32] On the
CR and on its southern flank, the sedimentary cover and trench fill
are thinner (0.5 e1.0 km) The prominent topographic feature of
the CR, which acts as a barrier and in fluences marine current
trajectories, sedimentary flux, deposition and the erosive power
of strong marine currents [27,33 e35] , explain this lack of
sedi-ment accumulation [30] Additionally, the coastal area close to the
CR subduction has been uplifted [36] inhibiting contribution for
trench sediment in flux from rivers coming from the Andes
[27,33 e35] To the south of the CR, the Guayaquil submarine
ba-sins exhibit up to 4 km of sediments [37 e39] Graindorge et al.
[40] found an over thickened (14 km) oceanic crust for the CR and
reported that the plate interface dips 4e10east from the trench
to a depth of 15 km, revealed by on-shore off-shore wide-angle
seismic pro files.
The regional pattern of seismicity and volcanism shows a high
degree of segmentation of the Andes along strike, as early noted by
Ref [27] In particular, along the Peru-Ecuador-Colombia margin
segment a steep slab subduction regime alternates with segments
of shallower subduction angles [27] , [41] Increased interplate
coupling related to the subduction of the thick, buoyant CR may
account for an apparent local increased recurrence interval
be-tween great interplate earthquakes [40]
Many authors have proposed a link between high sediment
thickness along the subducting margin and large ruptures
associ-ated with great megathrust earthquakes [6,42 e45] These works
propose that the subduction interface becomes smoothened
when high volumes of sediments are subducted, resulting in a homogenous plate interface that allows seismic ruptures to over-come bathymetric barriers favouring trench-parallel propagation.
Important changes in morphology of the subduction zone along the northern Perú-Ecuador and Colombia subduction zone have been attributed to a non-linearity of the subduction margin and subduction of bathymetric features with high- floatability in the subducted ocean floor While south of the Guayaquil Gulf a downward flexure has been attributed to an ocean ward convex subduction margin [41] , a mild shallowing of the Nazca Plate since 30 Ma north of it, determined from the consequent arc expansion to the plate interior, is attributed to the subduction of the CR [46]
A high obliquity between Nazca and South American plates decouples inland a forearc sliver through the arc zone that de fines a strike slip system associated with a strain partitioned regime, named the North Andean Sliver [26,47 e49] , ( Fig 2 ).
3 Methods 3.1 GOCE derived gravity data
We performed a direct modeling from satellite-only GOCE model GO_CONS_GCF_2_DIR_R5 [50] , a full combination of GOCE-SGG (Satellite Gravity Gradiometer), GOCE-SST (Satellite-to-Satel-lite Tracking), GRACE (Gravity Recovery and Climatic Experiment) and LAGEOS (Laser Geodynamics Satellite) data, leading to an excellent performance of the long as well as of the short wave-lengths processing details are given in Refs [2,3] This satellite only model obtained by the direct approach method, presents homo-geneous precision and it is the one of maximum degree/order (N ¼ 300) from satellite-only data The half-wavelength resolution
is of approximately 67 km according to l /2 ¼ p R/Nmax [51 e53] , with R being the mean Earth radius and Nmax the maximum de-gree/order of the harmonic expansion.
The observed potential is obtained from the global gravity field model Then, the disturbing potential (T) is derived by subtracting the potential field of the reference ellipsoid from the first [54] The gravity gradient tensor (Marussi tensor) is composed by five in-dependent elements and is obtained as the second derivative of the disturbing potential [52] We calculate the second derivative of the disturbing potential in the radial direction, or vertical gravity gradient (Tzz), from the spherical harmonic coef ficients [54] on a regular grid of 0.05 grid cell size The Tzz is expressed in E€otv€os (104mGal/m) and represents a better theoretical resolution than the gravity vector itself for some geophysical features [51] , allowing to determine the location of anomalous masses with better detail and accuracy [55] This methodology has already been used in Refs [6 e8,56,57] , with a detailed description pre-sented in Refs [58,59]
3.2 Topographic and sediment corrections The topographic effect must be removed from the satellite observations [60] in order to eliminate the correlation with the topography The effect generated by the topographic masses on the gravity field and its derivatives is calculated according to Newton's law of universal gravitation To remove the topographic effect from the vertical gravity gradient we performed the topo-graphic correction by discretizing a digital elevation model ETOPO1, using spherical prisms of constant density [15,61 e64] By
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
66 67 68 69 70 71 72 73 74 75 76 77 78 79 80 81 82 83 84 85 86 87 88 89 90 91 92 93 94 95 96 97 98 99 100 101 102 103 104 105 106 107 108 109 110 111 112 113 114 115 116 117 118 119 120 121 122 123 124 125 126 127 128
Trang 5using a spherical approximation instead of a planar one, we
considered the Earth's curvature [65] , avoiding considerable
er-rors as the region under study is large enough [52,58,59,64,66]
We performed calculation of the topography generated Tzz using
the software Tesseroids [59,65] Adopted densities are mean
standard values of 2.67 g/cm3for masses above sea level and a
1.03 g/cm3for sea water The calculation height is of 7000 m to
ensure that all values are above the topography The topographic
correction amounts up to tens of E€otv€os, with higher positive
values over the Andes and maximum negative values over the
lowest relief such as the trench ( Fig 3 a) The topographic effect
was filtered by using a 4th order Butterworth filter at 133 km
wavelength in order to reduce satellite data at comparable wavelengths ( Fig 3 b).
The sediment correction was performed using the same method considering a mean density of 2.4 g/cm3( Fig 4 a and b) Sediment thicknesses were obtained from NGDC's global ocean sediment thickness grid from Ref [67] , an updated version
of the NGDC's original ocean sediment thickness grid from Ref.
[68] The topography- and sediment-corrected vertical gravity gradient is shown in Fig 5 and in Fig 6 slip distribution is super-imposed (preliminary model taken from http://earthquake.usgs gov/earthquakes/eventpage/us20005j32# finite-fault ).
Fig 3 a) Computed direct topographic effect over the vertical gravity gradient signal b) Filtered topographic effect over the vertical gravity gradient signal
Fig 4 a) Computed sedimentary effect over the submerged accretionary prism and oceanfloor (sediment thicknesses taken from NOAA) b) Filtered offshore sediment effect over the gravity signal
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
66 67 68 69 70 71 72 73 74 75 76 77 78 79 80 81 82 83 84 85 86 87 88 89 90 91 92 93 94 95 96 97 98 99 100 101 102 103 104 105 106 107 108 109 110 111 112 113 114 115 116 117 118 119 120 121 122 123 124 125 126 127 128 129
Trang 63.3 Harmonic decomposition There is an approximate relationship between the associated depths of a causative mass with a determined degree of the spherical harmonic expansion [69] By cutting-off the degree/
order of the harmonic expansion allows to decompose the gravimetric signal as causative mass depth increases Feather-stone [69] related the depth (Zl) of a causative mass with a determined degree of the spherical harmonic expansion (N)
by performing a spectral analysis of the geoid and gravity anomalies.
In a recent work, we derived a similar equation (Eq (1) ) but relating Zlwith a determined N for gravity anomalies and vertical gravity gradient (see Ref [8] ) In this work, we calculated Tzz up to different degree/orders of the harmonic expansion in order to analyze the response with increasing depths.
Zl¼ ðREþ HcÞðN 1Þ
where REis the Earth's radius, HCis the Tzz calculation height and
N is the selected degree/order of the harmonic expansion Higher orders are associated with shallower sources (low Zl), while decreasing orders are related to deeper mass anomalies (higher
Zl) Table 1 shows the used degree/orders, the corresponding depth Zland spatial resolution, using RE¼ 6371 km as mean Earth radius Results from this harmonic decomposition tool (by trun-cating the harmonic expansion) allow analyzing Tzz response with increasing depths of the causative masses ( Fig 7 ) For the Musine earthquake, the best fit (between Tzz and slip distribution) is obtained with N between 175 (approximately 36 km depth) and
200 (approximately 31 km depth), while contrastingly, for the Illapel earthquake the best fit had been obtained for N between
225 and 250 [8] that would preliminarily be interpreted as a relatively deeper rupture Ye et al [25] inferred a minor deep asperity (at a depth of approximately 30 km) at the southeastern end of their slip model, being consistent with the causative mass depth found in this work (for the best fit between Tzz and slip
Fig 5 Vertical gravity gradient from GOCE data up to degree/order N¼ 300 after
removing thefiltered topographic and offshore sediment effects Red star indicates the
position of the epicenter associated with the Mw¼ 7.8 thrust earthquake on April 17,
2016 and white triangles indicate the volcanic arc as a reference
Fig 6 Detail of the vertical gravity gradient from GOCE data up to degree/order
N¼ 300 after removing topographic and offshore sediment effects, where
displace-ments (red numbers) in the rupture zone are depicted with solid white line contours
(preliminary slip model taken from http://earthquake.usgs.gov/earthquakes/
eventpage/us20005j32#finite-fault) Red star indicates epicenter
Table 1 Associated depth (Zl) of a causative mass with a determined degree of the spherical harmonic expansion for Tzz
Degree/order N Spatial resolutionl/2¼pR/Nmax(km) Zl(km) for Tzz Eq.(1)(Hc¼ 7 km)
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
66 67 68 69 70 71 72 73 74 75 76 77 78 79 80 81 82 83 84 85 86 87 88 89 90 91 92 93 94 95 96 97 98 99 100 101 102 103 104 105 106 107 108 109 110 111 112 113 114 115 116 117 118 119 120 121 122 123 124 125 126 127 128
Trang 7Fig 7 Topography and sediment corrected Tzz slices calculated at different degrees of the harmonic expansion Downwards: as degree/order decreases, exploration depths increase.
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
66 67 68 69 70 71 72 73 74 75 76 77 78 79 80 81 82 83 84 85 86 87 88 89 90 91 92 93 94 95 96 97 98 99 100 101 102 103 104 105 106 107 108 109 110 111 112 113 114 115 116 117 118 119 120 121 122 123 124 125 126 127 128 129
Trang 84 Conclusions
Vertical gravity gradients calculated from GOCE satellite data
corrected by sediment and topographic effects show a correlation
with the rupture area of the Mw ¼ 7.8 April 16, 2016 Ecuador
earthquake, for certain degrees of the harmonic expansion
(N ¼ 175/200) and related depth (Zlz 35/31 km) of the causative
mass.
This implies that heterogeneous density structure of the
decoupled Ecuador fore-arc could explain propagation of the
rupture zone In particular, the rupture zone of the Mw ¼ 7.8 April
16, 2016 Ecuador earthquake developed through a relatively low
density zone of the fore-arc sliver, such as for other cases along the
South American subduction zone has been recently noted.
Finally, aftershock sequence nucleated around the area of
maximum slips in the rupture zone Recent works [25] suggest that
asperities can be persistent features determined by the spatial
variations of the mechanical properties of the subduction
mega-thrust This observation implies that heterogeneous density
struc-ture of the fore-arc determined from gravity data could be used in
forecasting potential damaged zones.
Acknowledgments
Authors acknowledge the use of the GMT-mapping software of
reference [71] The authors would like to thank to CONICET.
References
[1] R Floberghagen, M Fehringer, D Lamarre, D Muzi, B Frommknecht,
C Steiger, J Pi~neiro, A Costa, Mission design, operation and exploitation of the
[2] R Pail, S Bruinsma, F Migliaccio, C F€orste, H Goiginger, W.D Schuh, E H€ock,
M Reguzzoni, J.M Brockmann, O Abrikosov, M Veicherts, T Fecher,
R Mayrhofer, I Krasbutter, F Sanso, C.C Tscherning, First GOCE gravity field models derived by three different approaches, J Geod 85 (2011) 819e843
[3] S.L Bruinsma, J.C Marty, G Balmino, R Biancale, C F€orste, O Abrikosov,
H Neumayer, GOCE gravityfield recovery by means of the direct numerical method, in: H Lacoste-Francis (Ed.), Proceedings of the ESA Living Planet Symposium, Norway, ESA Publication (27) SP-686, Bergen, 2010
[4] J.M Brockmann, N Zehentner, E Hock, R Pail, I Loth, T Mayer-Giirr, W.D Schuh, EGM_TIM_RW5: an independent geoid with centimeter accuracy purely based on the GOCE mission, Geophys Res Lett 41 (2014) 8089e8099
[5] M.J Fuchs, J Bouman, T Broerse, P Visser, B Vermeersen, Observing coseismic gravity change from the Japan Tohoku-Oki 2011 earthquake with GOCE gravity gradiometry, J Geophys Res Solid Earth 118 (2013) 1e10, http://
dx.doi.org/10.1002/jgrb.50381 [6] O Alvarez, S Nacif, M Gimenez, A Folguera, A Braitenberg, GOCE derived vertical gravity gradient delineates great earthquake rupture zones along the Chilean margin, Tectonophysics 622 (2014) 198e215, http://dx.doi.org/
10.1016/j.tecto.2014.03.011 [7] O Alvarez, S Nacif, S Spagnotto, A Folguera, M Gimenez, M Chlieh,
C Braitenberg, Gradients from GOCE reveal gravity changes before Pisagua
Mw¼ 8.2 and Iquique Mw ¼ 7.7 large megathrust earthquakes, J S Am Earth Sci 64P2 (2015) 15e29,http://dx.doi.org/10.1016/j.jsames.2015.09.014 [8] O Alvarez, A Pesce, M Gimenez, A Folguera, S Soler, C Wenjin, Analysis of the Illapel Mw¼ 8.3 thrust earthquake rupture zone using GOCE derived gradients, Pure Appl Geophys (2016),
[9] T.R Song, M Simons, Large trench-parallel gravity variations predict seis-mogenic behavior in subduction zones, Science 301 (2003) 630e633
[10] R.E Wells, R.J Blakely, Y Sugiyama, D.W Scholl, P.A Dinterman, Basin centered asperities in great subduction zone earthquakes: a link between slip, subsidence and subduction erosion? J Geophys Res 108 (B10) (2003) 2507e2536,http://dx.doi.org/10.1029/2002JB002072
[11] A.L Llenos, J.J Mc Guire, Influence of fore-arc structure on the extent of great subduction zone earthquakes, J Geophys Res 112 (2007) B09301
[12] M Sobiesak, U Meyer, S Schmidt, H.J G€otze, C Krawczyk, Asperity generating upper crustal sources revealed by b-value and isostatic residual anomaly grids
in the area of Antofagasta, J Geophys Res 112 (2007) B12308, http://
dx.doi.org/10.1029/2006JB004796 [13] A Maksymowicz, A Trehuc, E Contreras-Reyes, S Ruiz, Density-depth model
of the continental wedge at the maximum slip segment of the Maule Mw8.8
Fig 8 Detail of the vertical gravity gradient of GOCE data up to N¼ 175 after removing topographic and offshore sediment effects, with internal displacements in the rupture zone
(solid white line) Note the good correspondence (match) between low Tzz lobe with slip On the right corner (zoom) the aftershock sequence is plotted (up to June 6, 2016)
corresponding to colored circles over seismicity (grey circles) from USGS Catalog Note how this post-earthquake sequence traces lines of iso-displacements into the rupture zone,
surrounding patch of maximum slip A similar observation is arrived for the Illapel earthquake in central Chile[70]
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
66 67 68 69 70 71 72 73 74 75 76 77 78 79 80 81 82 83 84 85 86 87 88 89 90 91 92 93 94 95 96 97 98 99 100 101 102 103 104 105 106 107 108 109 110 111 112 113 114 115 116 117 118 119 120 121 122 123 124 125 126 127 128
Trang 9[14] A Tassara, Control of forearc density structure on megathrust shear strength
along the Chilean subduction zone, Tectonophysics 495 (2010) 34e47,http://
dx.doi.org/10.1016/j.tecto.2010.06.004
[15] C Amante, B.W Eakins, ETOPO1, 1 Arc-Minute Global Relief Model:
Proced-ures, Data Sources and Analysis NOAA Technical Memorandum NESDIS
NGDC-24, 2009, p 19 March 2009
[16] L Siebert, T Simkin, Volcanoes of the World: An Illustrated Catalog of
Holo-cene Volcanoes and their Eruptions Smithsonian Institution, Global
Volca-nism Program Digital Information Series, GVP-3, 2002.http://www.volcano.si
edu/world/
[17] M Chlieh, P.A Mothes, J.M Nocquet, P Jarrin, P Charvis, D Cisneros, Y Font,
J.Y Collot, J.C Villegas-Lanza, F Rolandone, M Vallee, M Regnier, M Segovia,
X Martin, H Yepes, Distribution of discrete seismic asperities and aseismic
slip along the Ecuadorian Megathrust, Earth Planet Sci Lett 400 (2014) (2014)
292e301
[18] F Megard, Cordilleran Andes and Marginal Andes: a review of Andean
geol-ogy North of Arica elbow (1800), in: J.W.H Monger, Francheteau (Eds.),
Circum-Pacific Orogenic Belts and Evolution of the Circum-Pacific Ocean Basin, J Geodyn Ser.,
vol 18, Am Geophys Union, Washington, DC, 1987
[19] D.G Herd, T.L Youd, H Meyer, J.L Arango, C.W.J Person, C Mendoza, The
great Tumaco, Colombia earthquake of 12 December 1979, Science 211 (1981)
441e445
[20] H Kanamori, K.C McNally, Variable rupture mode of the subduction zone
along the EcuadoreColombia coast, Bull Seismol Soc Am 72 (4) (1982)
1241e1253
[21] S.L Beck, L.J Ruff, The rupture process of the great 1979 Colombia
earthquake-evidence for the asperity model, J Geophys Res 89 (1984)
9281e9291
[22] C Mendoza, J.W Dewey, Seismicity associated with the great
Colombia-eEcuador earthquakes of 1942, 1958 and 1979: implications for barrier
models of earthquake rupture, Bull Seismol Soc Am 74 (2) (1984) 577e593
[23] J.L Swenson, S.L Beck, Historical 1942 Ecuador and 1942 Peru subduction
earthquakes, and earthquake cycles along ColombiaeEcuador and Peru
sub-duction segments, Pure Appl Geophys 146 (1) (1996) 67e101
[24] J.-Y Collot, B Marcaillou, F Sage, F Michaud, W Agudelo, P Charvis,
D Graindorge, M.A Gutscher, G Spence, Are rupture zone limits of great
subduction earthquakes controlled by upper plate structures? Evidences from
multichannel seismic reflection data acquired across the northern
Ecua-doresouthwest Colombia margin, J Geophys Res (2004) 109
[25] L Ye, H Kanamori, J.P Avouac, L Li, K.F Cheung, T Lay, The 16 April 2016,
MW 7.8 (MS 7.5) Ecuador earthquake: a quasi-repeat of the 1942 MS 7.5
earthquake and partial re-rupture of the 1906 MS 8.6 ColombiaeEcuador
earthquake, Earth Planet Sci Lett 454 (2016) 248e258,http://dx.doi.org/
10.1016/j.epsl.2016.09.006
[26] J.M Nocquet, J.C Villegas-Lanza, M Chlieh, P.A Mothes, F Rolandone, P Jarrin,
D Cisneros, A Alvarado, L Audin, F Bondoux, X Martin, Y Font, M Regnier,
M Vallee, T Tran, C Beauval, J.M Magui~na Mendoza, W Martinez, H Tavera,
H Yepes, Motion of continental slivers and creeping subduction in the
northern Andes, Nat Geosci 7 (2014) 287e291
[27] M.A Gutscher, J Malavieille, S Lallemand, J.Y Collot, Tectonic segmentation of
the North Andean margin: impact of the Carnegie Ridge collision, Earth Planet
Sci Lett 168 (1999) 255e270
[28] B Marcaillou, Regimes tectoniques et thermiques de la marge Nord
Equateur-Sud Colombie (0e3.5N)e Implications sur la sismogenese, These de
Doc-torat, Universite Pierre et Marie Curie (Paris VI), 2003
[29] A Calahorrano, Structure de la marge du Golfe de Guayaquil (Equateur) et
proprietes physiques du chenal de subduction a partir de donnees de
sismi-que marine reflexion et refraction, These de Doctorat, Universite Pierre et
Marie Curie (Paris VI), 2005
[30] A Gailler, P Charvis, E.R Flueh, Segmentation of the Nazca and South
American plates along the Ecuador subduction zone from wide-angle seismic
profiles, Earth Planet Sci Lett 260 (2007) 444e464
[31] P Lonsdale, K.D Klitgord, Structure and tectonic history of the eastern
Pan-ama Basin, Geol Soc Am Bull 89 (1978) 981e999
[32] T.W Gardner, D Verdonck, N.M Pinter, R Slingerland, K.P Furlong,
T.F Bullard, S.G Wells, Quaternary uplift astride the aseismic Cocos Ridge,
Pacific coast, Costa Rica, Geol Soc Am Bull 104 (1992) 219e232
[33] J.Y Collot, P Charvis, M.A Gutscher, S Operto, The Sisteur scientific party,
exploring the EcuadoreColombia active margin and inter-plate seismogenic
zone, EOS 83 (185) (2002) 189e190
[34] A.C Mix, R Tiedemann, P Blum, shipboard scientists (Eds.), Southeast Pacific
Paleoceanographic Transects Sites 1232e1242, ODP Leg 202, 2002
[35] F Michaud, A Chabert, J.-Y Collot, V Sallares, E.R Flueh, P Charvis,
D Graindorge, M.-A Gustcher, J Bialas, Fields of multi-kilometer scale
sub-circular depressions in the Carnegie ridge sedimentary blanket: effect of
un-derwater carbonate dissolution? Mar Geol 216 (2005) 205e219
[36] T De Vries, The geology of late Cenozoic marine terraces (tablazos) in
northwestern Peru, J South Am Earth Sci 1 (1988) 121e136
[37] Y Deniaud, P Baby, C Basile, M Ordo~nez, G Montenegro, G Mascle,
Ouver-ture et evolution tectono-sedimentaire du golfe de Guayaquil: basin
d'avant-arc neogene et quaternaire du Sud des Andes equatoriennes, Acad Sci Paris
328 (1999) 181e187
[38] C Witt, J Bourgois, F Michaud, M Ordo~nez, N Jimenez, M Sosson,
Devel-opment of the Gulf of Guayaquil (Ecuador) during the quaternary as an effect
of the North Andean block tectonic escape, Tectonics 25 (2006) TC3017, http://dx.doi.org/10.1029/2004TC001723
[39] A Alvarado, L Audin, J.M Nocquet, E Jaillard, P Mothes, P Jarrín, M Segovia,
F Rolandone, D Cisneros, Partitioning of oblique convergence in the Northern Andes subduction zone: migration history and the present-day boundary of the North Andean Sliver in Ecuador, Tectonics 35 (2016) 1048e1065,http:// dx.doi.org/10.1002/2016TC004117
[40] D Graindorge, A Calahorrano, P Charvis, J.Y Collot, N Bethoux, Deep struc-tures of the Ecuador convergent margin and the Carnegie Ridge, possible consequence on great earthquakes recurrence interval, Geophys Res Lett Solid Earth 31 (4) (2004),http://dx.doi.org/10.1029/2003GL018803
[41] H Yepes, L Audin, A Alvarado, C Beauval, J Aguilar, Y Font, F Cotton, A new view for the geodynamics of Ecuador: implication in seismogenic source definition and seismic hazard assessment, Tectonics 35 (2016) 1249e1279, http://dx.doi.org/10.1002/2015TC003941
[42] E Contreras-Reyes, E Flueh, L Grevemeyer, Tectonic control on sediment accretion and subduction off south-central Chile: implications for coseismic rupture processes of the 1960 and 2010 megathrust earthquakes, Tectonics 29 (2010) TC6018
[43] A Heuret, C.P Conrad, F Funiciello, S Lallemand, L Sandri, Relation between subduction megathrust earthquakes, trench sediment thickness and upper plate strain, Geophys Res Lett 39 (2012) L05304,http://dx.doi.org/10.1029/ 2011GL050712
[44] L.J Ruff, Do trench sediments affect great earthquake occurrence in subduc-tion zones? Pure Appl Geophys 129 (1989) 263e282
[45] M Schertwath, E Contreras-Reyes, E Flueh, J Grevemeyer, A Krabbenhoeft,
C Papenberg, C Petersen, R.W Weinrebe, Deep lithospheric structures along the southern central Chile margin from wide-angle P-wave modelling, Geo-phys J Int 179 (1) (2009) 579e600
[46] S Echeverri, A Cardona, A Pardo-Trujillo, S Lopez, Regional rovenance from southwestern Colombia Fore-arc and intra-arc basins: implications for middle
to late miocene orogeny in the Northern Andes, Terranova 27 (5) (2015), http://dx.doi.org/10.1111/ter 12167
[47] W Pennington, Subduction of the Eastern Panama Basin and seismotectonics
of northwestern South America, J Geophys Res 86 (B11) (1981) 10,753e10,770,http://dx.doi.org/10.1029/JB086iB11p10753
[48] C Costa, F Audemard, L Audin, C Benavente, Geomorphology as a tool for analysis of seismogenic sources in Latin America and the Caribbean, in:
E Latrubesse (Ed.), Natural Hazards and Human-Exacerbated Disasters in Latin America, Elsevier, 2009, pp 30e46
[49] O Egbue, L Kellogg, Pleistocene to present North Andean‘escape’, Tectono-physics 489 (2010) 248e257,http://dx.doi.org/10.1016/j.tecto.2010.04.021 [50] S.L Bruinsma, C F€orste, O Abrikosov, J.C Marty, M.H Rio, S Mulet,
S Bonvalot, The new ESA satellite-only gravityfield model via the direct approach, Geophys Res Lett 40 (2013) 3607e3612
[51] X Li, Vertical resolution: gravity versus vertical gravity gradient, Lead Edge 20 (2001) 901e904
[52] B Hofmann-Wellenhof, H Moritz, Phys Geod., 2nd ed., Springer, Berlin, 2006,
p 286
[53] F Barthelmes, Definition of Functionals of the Geopotential and Their Calcu-lation from Spherical Harmonic Models Theory and Formulas Used by the Calculation Service of the International Centre for Global Earth Models (ICGEM), 2013 Scientific Technical Report, STR09/02, Revised edition, January
2013 GFZ German Research Centre for Geosciences, Potsdam, Germany World Wide Web Address,http://icgem.gfz-postdam.de/ICGEM
[54] J Janak, M Sprlak, New software for gravityfield modelling using spherical armonic, Geod Cartog Hor 52 (2006) 1e8 (in Slovak)
[55] C Braitenberg, P Mariani, J Ebbing, M Sprlak, The enigmatic Chad lineament revisited with global gravity and gravity-gradientfields, in: D.J.J Van Hins-bergen, S.J.H Buiter, T.H Torsvik, C Gaina, S.J Webb (Eds.), The Formation and Evolution of Africa: A Synopsis of 3.8 Ga of Earth History, Geol Soc London Spec Publ., vol 357, Geological Society, London, 2011, pp 329e341,http:// dx.doi.org/10.1144/SP357.18
[56] O Alvarez, M.E Gimenez, M.P Martinez, F LinceKlinger, C Braitenberg, New insights into the Andean crustal structure between 32and 34S from GOCE satellite gravity data and EGM2008 model, in: S.A Sepúlveda, L.B Giambiagi, S.M Moreiras, L Pinto, M Tunik, G.D Hoke, M Farías (Eds.), Geodynamic Processes in the Andes of Central Chile and Argentina, Geological Society, London, Special Publications, vol 399, 2015, pp 183e202,http://dx.doi.org/ 10.1144/SP399.3
[57] O Alvarez, M Gimenez, A Folguera, S Spagnotto, E Bustos, W Baez,
C Braitenberg, New evidence about the subduction of the Copiapo ridge beneath South America, and its connection with the Chilean-Pampeanflat slab, tracked by satellite GOCE and EGM2008 models, J Geodyn 91C (2015) 65e88,http://dx.doi.org/10.1016/j.jog.2015.08.002
[58] O Alvarez, M.E Gimenez, C Braitenberg, A Folguera, GOCE satellite derived gravity and gravity gradient corrected for topographic effect in the South Central Andes region, Geophys J Int 190 (2) (2012) 941e959, http:// dx.doi.org/10.1111/j.1365-246X.2012.05556.x
[59] O Alvarez, M.E Gimenez, C Braitenberg, Nueva metodología para el calculo del efecto topografico para la correccion de datos satelitales, Rev Asoc Geol Arg 70 (4) (2013) 422e429
[60] R Forsberg, C.C Tscherning, Topographic effects in gravity modeling for BVP, in: F Sanso, R Rummel (Eds.), Geodetic Boundary Value Problems in View of
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
66 67 68 69 70 71 72 73 74 75 76 77 78 79 80 81 82 83 84 85 86 87 88 89 90 91 92 93 94 95 96 97 98 99 100 101 102 103 104 105 106 107 108 109 110 111 112 113 114 115 116 117 118 119 120 121 122 123 124 125 126 127 128 129
Trang 10the One Centimeter Geoid, Lecture Notes in Earth Science, vol 65,
Springer-Verlag, Berlin, 1997, pp 241e272
[61] B Heck, K Seitz, A comparison of the tesseroid, prism and point mass
ap-proaches for mass reductions in gravityfield modeling, J Geod 81 (2) (2007)
121e136,http://dx.doi.org/10.1007/s00190-006-0094-0
[62] F Wild-Pfeiffer, A comparison of different mass element for use in gravity
gradiometry, J Geod 82 (2008) 637e653,
http://dx.doi.org/10.1007/s00190-008-0219-8
[63] T Grombein, B Heck, K Seitz, Untersuchungen zur effizienten Berechnung
topographischer Effekte auf den Gradiententensor am Fallbeispiel der
Satel-liten gradiometrie mission GOCE, Karlsruhe Institute of Technology, KIT, 2010,
pp 1e94 Scientific Reports 7547, ISBN 978-3-86644-510-9
[64] T Grombein, B Heck, K Seitz, Optimized formulas for the gravitationalfield of
a tesseroid, J Geod 87 (2013), 645e600
[65] L Uieda, N Ussami, C.F Braitenberg, Computation of the gravity gradient
tensor due to topographic masses using tesseroids, Eos Trans AGU 91 (26)
(2010) Meeting America Supply, Abstract G22A-04 World Wide Web
Address,http://code.google.com/p/tesseroids/
[66] J Bouman, J Ebbing, M Fuchs, Reference frame transformation of satellite
gravity gradients and topographic mass reduction, J Geophys Res Solid Earth
118 (2) (2013) 759e774,http://dx.doi.org/10.1029/2012JB009747
[67] J Whittaker, A Goncharov, S Williams, R.D Müller, G Leitchenkov, Global
sediment thickness dataset updated for the Australian-Antarctic Southern
Ocean, Geochem Geophys Geosystems 14 (2013) 3297e3305, http://
dx.doi.org/10.1002/ggge.20181
[68] D.L Divins, Total Sediment Thickness of the World's Oceans and Marginal Seas, NOAA National Geophysical Data Center, Boulder, CO, 2003
[69] W Featherstone, On the use of the geoid in geophysics: a case study over the north west shelf of Australia, Explor Geophys 28 (1/2) (1997) 52e57
[70] F Tilmann, Y Zhang, M Moreno, J Saul, F Eckelmann, M Palo, Z Deng,
A Babeyko, K Chen, J.C Baez, B Schurr, R Wang, T Dahm, The 2015 Illapel earthquake, central Chile: a type case for a characteristic earthquake? Geo-phys Res Lett 43 (2016) 574e583,http://dx.doi.org/10.1002/2015GL066963 [71] P Wessel, W.H.F Smith, New, improved version of the generic mapping tools released, Eos Trans AGU 79 (47) (1998) 579
Orlando Alvarez Pontoriero, Doctor in Geophysics Cur-rent position as Assistant Researcher at CONICET and Professor at Instituto Geofísico y Sismologico Ing F.S
Volponi, Facultad de Ciencias Exactas Fisicas y Naturales, Universidad Nacional de San Juan His current research is the study of great megathrust earthquakes rupture zones and its relation to Satellite Gravity Other Research in-terests: Geophysics, Geodynamics, Subduction zones, Earthquakes forecasting and prediction
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36