33.0˚ 34.0˚ 35.0˚ −11.0˚ −10.0˚ −9.0˚ 33.6˚ 33.7˚ 33.8˚ 33.9˚ 34.0˚ −10.0˚ −9.9˚ −9.8˚ −9.7˚ −9.6˚ Deciphering the role of fluids in early stage rifting from full moment tensor inversion of East African earthquakes S.J. Oliva 1 ([email protected]), C.J. Ebinger 1 , S.W. Roecker 2 , D.B. Keir 3 , D.J. Shillington 4 , P. Chindandali 5 1 U. of Rochester (USA), 2 Rensselaer Polytechnic Inst. (USA), 3 U. of Southampton (UK), 4 LDEO, Columbia U. (USA), 5 Geological Survey of Malawi (Malawi) 1. Introduction 3. Magmatic sector: Kenya - Northern Tanzania 5. Discussion 2. Full moment tensor inversion The East African Rift splits around the Archaean Tanzania craton into the magmatic Eastern branch and the mostly amagmatic Western branch. The EARS is the site of lower crustal EQs and active magma intrusion, enabling detection of a broad range of rifting processes and providing insights into the early rifting. Focus: Is brittle strain accommodated by shear in magmatic and amagmatic rift sectors, or do magma and volatile flow add a significant isotropic component? Are there differences between unusual lower crustal EQs and shallow EQs? (Adapted from Dawson, 2008) 4. Amagmatic sector: Northern Malawi Acknowledgments ✦ Dreger & Ford TDMT algorithm ✦ full waveforms, TRV components ✦ MT decompositions capture different mechanisms ✦ DC : shear faulting ✦ ISO : tensile opening ✦ CLVD : non-∆V DC deviation ✦ uses a 1D velocity model ✦ from a seismic line, north of the region ✦ largest variance reduction = best fit ✦ improved source depth estimate ✦ bp filter 0.02 - 0.10 Hz, or range within ✦ non-ISO vs ISO solution: ✦ EVT1 and EVT2: Two significant-sized EQs within a day of the same mechanism, with a big isotropic component as shown in this inversion = an intrusion? — awaiting inSAR results on this ✦ Suggests reinterpretation of shallow magma chamber of the Biggs et al (2009, 2013) geodetic model based on InSAR Full moment tensor inversion uses Dreger and Ford TDMT-INVC algorithm (Dreger, 2003; Minson & Dreger, 2008). Many thanks to N. Lindsey for assistance in learning this code. Support from NSF, ANR, IRIS/PASSCAL gratefully acknowledged. 36 -3 -2.5 < 5 <10 <15 <20 <30 <40 <50 Gelai Songo b.f. NATRON BASIN OL NS Lo F1 F3 Manyara b.f K Kitumbeine Engaruka tf F2 F4 Em C C’ C C’ -30 -20 -10 0 2.5 3.0 3.5 4.0 Vs -25 -15 -5 0 10 20 30 40 50 60 5 0 1 2 3 S. flank Gelai volcano Naibor Soito monogenetic cones N. flank, Oldoinyo Lengai volcano Songo border fault Natron Basin km km km W E 2007 dike intrusion Mw5.9 36E magma body 17/7/2007 magma body sedimentary strata Mosonik v B B’ B B’ Manyara basin magma intrusion zone local stress field rotation RIFT SEGMENT LINKAGE VIA MAGMA INTRUSION strain by slip along border fault strain by magma intrusion and slip along border fault Gelai volcano Gelai dike intrusion zone ? Oldoinyo Lengai ca. 15 km Naibor Soito monogenetic cones NS OL Border fault Magadi basin Natron basin ✦ Geometry of earthquakes close to the region of the 2007 diking could be indicative of a sill (Weinstein et al, submitted) ✦ Strain accommodation via non-DC mechanisms (indicative of fluids?) supports the magma-driven model of rifting Tanganyika rift Malawi rift ✦ ISO component can be significant, important to consider ✦ May be indicative of fluid activity T51C-2942 35.8˚ 35.9˚ 36.0˚ 36.1˚ 36.2˚ −2.9˚ −2.8˚ −2.7˚ −2.6˚ −2.5˚ 35.0˚ 36.0˚ 37.0˚ 38.0˚ −6.0˚ −5.0˚ −4.0˚ −3.0˚ −2.0˚ −1.0˚ M1 M2 M3 M4 M5 Gelai Oldoinyo Lengai Kerimasi border fault EVT1 EVT2 EVT3 EVT4 EVT5 EVT6 0 5 10 15 20 25 30 35 40 Depth (km) Sample waveform fits Event EVT1 2013-06-03 03:24 Ml 4.40, 8 km depth % DC 30 % CLVD 32 % ISO 39 MW43.data 30.00 sec LN46.data 30.00 sec LN25.data 30.00 sec NBI.data 30.00 sec EVT2 2013-06-03 09:53 Ml 4.38, 8 km depth EVT3 2014-08-04 03:06 Ml 3.68, 11 km depth % DC 48 % CLVD 40 % ISO 12 EVT4 2014-09-05 17:54 Ml 3.60, 8 km depth % DC 37 % CLVD 28 % ISO 36 % DC 33 % CLVD 42 % ISO 25 EVT5 2014-09-19 19:50 Ml 3.50, 7 km depth % DC 65 % CLVD 30 % ISO 5 EVT6 2014-10-31 17:50 Ml 5.1, 21 km depth % DC 49 % CLVD 29 % ISO 31 PR11.data 30.00 sec MW36.data 30.00 sec LL23.data 30.00 sec PR33.data 30.00 sec LL24.data 22.50 sec LL23.data 22.50 sec LL22.data 22.50 sec KEN3.data 22.50 sec LL24.data 22.50 sec LL22.data 22.50 sec KEN3.data 22.50 sec NG55.data 22.50 sec PR31.data 22.50 sec PR11.data 22.50 sec MW44.data 22.50 sec LL65.data 22.50 sec LL65.data 22.50 sec LOSI.data 22.50 sec MBAR.data 22.50 sec PR52.data 22.50 sec deviatoric solution isotropic solution EVT1-Tanz EVT2-Tanz EVT7-Mlwi % DC 99 % CLVD 1 % ISO 0 % DC 30 % CLVD 32 % ISO 39 % DC 98 % CLVD 2 % ISO 0 % DC 37 % CLVD 28 % ISO 36 % DC 53 % CLVD 28 % ISO 19 % DC 89 % CLVD 11 % ISO 0 Sample waveform fits Event EVT7 2014-12-31 19:47 Mw 5.1, 6 km depth % DC 53 % CLVD 28 % ISO 19 EVT8 2014-12-31 20:41 5 km depth % DC 61 % CLVD 33 % ISO 6 EVT9 2015-01-01 00:33 10 km depth % DC 52 % CLVD 42 % ISO 6 ZINI.data 30.00 sec MBAM.data 30.00 sec WINO.data 30.00 sec GAWA.data 30.00 sec KALO.data 22.50 sec KARM.data 22.50 sec UWEM.data 22.50 sec NKAL.data 22.50 sec NGON.data 22.50 sec MLOW.data 22.50 sec LOSI.data 22.50 sec IGOM.data 22.50 sec EVT9 EVT7 EVT8 0 5 10 15 20 25 30 35 40 Depth (km) ✦ CRAFTI broadband seismic array, 2013-2014 ✦ M > 3.5 with good azimuthal coverage (for EVT6, the SEGMeNT array in SW complements CRAFTI) ✦ EVT1-5, source-to-receiver distances < 200 km ✦ SEGMeNT array, 2014-12-31 EQ sequence ✦ EVT7-9, source-to-receiver distances < 200 km ✦ Shallow extensional and strike-slip events, similar to 2009 Karonga sequence ✦ Unruptured segment during the 2009 sequence? Though not as strong ✦ Shallow Mw5.1 EQ may have triggered slip on faults in lower crust, with strike-slip mechanisms possibly associated with linkage to faults that slipped in 2009 ✦ First motion analyses of full aftershock sequence to test fault linkage hypothesis ✦ Smaller volumetric components of FMT in amagmatic compared to magmatic sectors, suggesting less fluid activity or different mechanism of activity ✦ Significant CLVD in all FMTs probably due to fluids (Weinstein et al, 2016) (Weinstein et al, 2016) (Adapted from Gaherty et al, AGU 2012; Faults after Ebinger 1993; Mortimer et al, 2007; Biggs et al, 2010; Bathymetry from Lyons et al, 2011) Rungwe Lake Malawi (Lake Nyasa) Karonga Livingstone fault 12/12/2009 12/08/2009 12/06/2009 12/19/2009
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33.0˚ 34.0˚ 35.0˚−11.0˚
−10.0˚
−9.0˚
33.6˚ 33.7˚ 33.8˚ 33.9˚ 34.0˚−10.0˚
−9.9˚
−9.8˚
−9.7˚
−9.6˚
Deciphering the role of fluids in early stage rifting from full moment tensor inversion of East African earthquakes S.J. Oliva1 ([email protected]), C.J. Ebinger1, S.W. Roecker2, D.B. Keir3, D.J. Shillington4, P. Chindandali5
1U. of Rochester (USA), 2Rensselaer Polytechnic Inst. (USA), 3U. of Southampton (UK), 4LDEO, Columbia U. (USA), 5Geological Survey of Malawi (Malawi)
1. Introduction 3. Magmatic sector: Kenya - Northern Tanzania 5. Discussion
2. Full moment tensor inversion
The East African Rift splits around the Archaean Tanzania craton into the magmatic Eastern branch and the mostly amagmatic Western branch. The EARS is the site of lower crustal EQs and active magma intrusion, enabling detection of a broad range of rifting processes and providing insights into the early rifting.
Focus: Is brittle strain accommodated by shear in magmatic and amagmatic rift sectors, or do magma and volatile flow add a significant isotropic component? Are there differences between unusual lower crustal EQs and shallow EQs?
(Adapted from Dawson, 2008)
Chapter 1
Introduction
There are only a few areas on Earth where continental platebreak-up and the attendant magmatism are taking place at thepresent day. In this context, the East African Rift system takespride of place as it is the most extensive, presently active,continental extension zone, the extension being accompanied
by seismicity, crustal thinning and, in some sectors, magmatism.The reason for this spectacular fracturing of the African Platehas been the subject of much debate but there is general consensusthat it is due, at least in part, to the presence of rising thermalplumes in the mantle beneath Africa. The extension is now held
Fig. 1.1. Map of East Africa, showing the plate tectonic position of the North Tanzania Divergence relative to the Red Sea spreading centre, and the main structural units
of the Ethiopian and Kenya domes and the Tanzania Craton.
J. B. Dawson, University of Edinburgh ( [email protected])From: DAWSON, J. B. 2008. The Gregory Rift Valley and Neogene–Recent Volcanoes of Northern Tanzania. Geological Society, London, Memoirs, 33, 1–2.
0435-4052/08/$15.00 # The Geological Society of London 2008. DOI: 10.1144/M33.1
at Marie Curie Library - The Abdus Salam ICTP on July 20, 2015http://mem.lyellcollection.org/Downloaded from
4. Amagmatic sector: Northern Malawi
Acknowledgments
✦ Dreger & Ford TDMT algorithm ✦ full waveforms, TRV components ✦ MT decompositions capture different mechanisms
✦ DC : shear faulting ✦ ISO : tensile opening ✦ CLVD : non-∆V DC deviation
✦ uses a 1D velocity model ✦ from a seismic line, north of the region
✦ largest variance reduction = best fit ✦ improved source depth estimate ✦ bp filter 0.02 - 0.10 Hz, or range within ✦ non-ISO vs ISO solution:
✦ EVT1 and EVT2: Two significant-sized EQs within a day of the same mechanism, with a big isotropic component as shown in this inversion = an intrusion? — awaiting inSAR results on this
✦ Suggests reinterpretation of shallow magma chamber of the Biggs et al (2009, 2013) geodetic model based on InSAR
Full moment tensor inversion uses Dreger and Ford TDMT-INVC algorithm (Dreger, 2003; Minson & Dreger, 2008). Many thanks to N. Lindsey for assistance in learning this code. Support from NSF, ANR, IRIS/PASSCAL gratefully acknowledged.
36
-3
-2.5
< 5<10<15<20<30<40<50
Gelai
Songob.f.
NATRONBASIN
OLNS
Lo
F1F3
Manyarab.f
K
Kitumbeine
Engaruka tf
F2
F4
Em
C C’
C C’
-30
-20
-10
0
2.5 3.0 3.5 4.0
Vs
�
� ��
��
����
�
-25
-15
-5
0 10 20 30 40 50 60
5
0
1
2
3
S. flank Gelai volcano
NaiborSoito monogenetic cones
N. flank, OldoinyoLengai volcano
Songo borderfault
Natron Basin
km
km
km
W E2007 dike intrusion
Mw5.9
36E
magma body
17/7/2007
�
��
��
���
magma body
sedimentary strata
Mosonik
v
B B’
B B’
Manyarabasin
magma intrusion zone local stress field rotation
RIFTSEGMENTLINKAGE VIA MAGMAINTRUSION
strainby slip alongborder fault
strainby magma intrusionand slip alongborder fault
Gelai volcano
Gelai
dike intrusion zone
?
OldoinyoLengai
ca. 15 km
Naibor Soitomonogeneticcones
NSOL
Border fault
Magadibasin
Natronbasin
✦ Geometry of earthquakes close to the region of the 2007 diking could be indicative of a sill (Weinstein et al, submitted)
✦ Strain accommodation via non-DC mechanisms (indicative of fluids?) supports the magma-driven model of rifting
Tanganyika rift
Malawi rift
✦ ISO component can be significant, important to consider ✦ May be indicative of fluid activity
T51C-2942
35.8˚ 35.9˚ 36.0˚ 36.1˚ 36.2˚−2.9˚
−2.8˚
−2.7˚
−2.6˚
−2.5˚
35.0˚ 36.0˚ 37.0˚ 38.0˚−6.0˚
−5.0˚
−4.0˚
−3.0˚
−2.0˚
−1.0˚
M1M2M3M4M5
Gelai
Oldoinyo Lengai
Kerimasi
border fault
EVT1
EVT2
EVT3
EVT4
EVT5
EVT6
0 5 10 15 20 25 30 35 40 45 50Depth (km)
Tangential Radial Vertical
MW43.data
Distance = 33 km Azimuth = 211 Max Amp = 1.39e−03 cm Zcorr = 7 VR = 50 30.00 sec
LN46.data
Distance = 64 km Azimuth = 96 Max Amp = 8.46e−04 cm Zcorr = 11 VR = 73 30.00 sec
LN26.data
Distance = 44 km Azimuth = 326 Max Amp = 4.12e−03 cm Zcorr = 6 VR = 39 30.00 sec
LN25.data
Distance = 54 km Azimuth = 334 Max Amp = 3.77e−03 cm Zcorr = 7 VR = 48 30.00 sec
LN14.data
Distance = 66 km Azimuth = 32 Max Amp = 4.44e−04 cm Zcorr = 9 VR = 6 30.00 sec
LL24.data
Distance = 82 km Azimuth = 337 Max Amp = 8.01e−04 cm Zcorr = 9 VR = −16 30.00 sec
�
page 1 of 2
Tangential Radial Vertical
PR63.data
Distance = 63 km Azimuth = 245 Max Amp = 6.84e−05 cm Zcorr = 4 VR = 0 22.50 sec
PR61.data
Distance = 89 km Azimuth = 255 Max Amp = 5.84e−05 cm Zcorr = 7 VR = 33 22.50 sec
NG55.data
Distance = 57 km Azimuth = 221 Max Amp = 1.15e−04 cm Zcorr = 6 VR = 66 22.50 sec
MW43.data
Distance = 51 km Azimuth = 189 Max Amp = 1.60e−04 cm Zcorr = 5 VR = 53 22.50 sec
LN15.data
Distance = 23 km Azimuth = 54 Max Amp = 3.11e−04 cm Zcorr = 0 VR = 23 22.50 sec
LL24.data
Distance = 58 km Azimuth = 336 Max Amp = 1.71e−04 cm Zcorr = 4 VR = 85 22.50 sec
�
page 1 of 2
Tangential Radial Vertical
NG55.data
Distance = 60 km Azimuth = 217 Max Amp = 2.34e−04 cm Zcorr = 6 VR = 57 22.50 sec
NG54.data
Distance = 72 km Azimuth = 268 Max Amp = 8.06e−05 cm Zcorr = 6 VR = 50 22.50 sec
LN26.data
Distance = 18 km Azimuth = 307 Max Amp = 2.29e−04 cm Zcorr = 2 VR = 34 22.50 sec
LN25.data
Distance = 27 km Azimuth = 329 Max Amp = 1.95e−04 cm Zcorr = 3 VR = 39 22.50 sec
LN15.data
Distance = 21 km Azimuth = 65 Max Amp = 2.16e−04 cm Zcorr = 0 VR = 29 22.50 sec
LN14.data
Distance = 54 km Azimuth = 56 Max Amp = 7.62e−05 cm Zcorr = 6 VR = 76 22.50 sec
✦ Shallow extensional and strike-slip events, similar to 2009 Karonga sequence
✦ Unruptured segment during the 2009 sequence? Though not as strong
✦ Shallow Mw5.1 EQ may have triggered slip on faults in lower crust, with strike-slip mechanisms possibly associated with linkage to faults that slipped in 2009
✦ First motion analyses of full aftershock sequence to test fault linkage hypothesis
✦ Smaller volumetric components of FMT in amagmatic compared to magmatic sectors, suggesting less fluid activity or different mechanism of activity
✦ Significant CLVD in all FMTs probably due to fluids
(Weinstein et al, 2016)
(Weinstein et al, 2016)
(Adapted from Gaherty et al, AGU 2012; Faults after Ebinger 1993; Mortimer et al, 2007; Biggs et al, 2010; Bathymetry from Lyons et al, 2011)
Tangential Radial Vertical
MW43.data
Distance = 33 km Azimuth = 211 Max Amp = 1.39e−03 cm Zcorr = 7 VR = 50 30.00 sec
LN46.data
Distance = 64 km Azimuth = 96 Max Amp = 8.46e−04 cm Zcorr = 11 VR = 73 30.00 sec
LN26.data
Distance = 44 km Azimuth = 326 Max Amp = 4.12e−03 cm Zcorr = 6 VR = 39 30.00 sec
LN25.data
Distance = 54 km Azimuth = 334 Max Amp = 3.77e−03 cm Zcorr = 7 VR = 48 30.00 sec
LN14.data
Distance = 66 km Azimuth = 32 Max Amp = 4.44e−04 cm Zcorr = 9 VR = 6 30.00 sec
LL24.data
Distance = 82 km Azimuth = 337 Max Amp = 8.01e−04 cm Zcorr = 9 VR = −16 30.00 sec
�
page 1 of 2
Tangential Radial Vertical
PR63.data
Distance = 63 km Azimuth = 245 Max Amp = 6.84e−05 cm Zcorr = 4 VR = 0 22.50 sec
PR61.data
Distance = 89 km Azimuth = 255 Max Amp = 5.84e−05 cm Zcorr = 7 VR = 33 22.50 sec
NG55.data
Distance = 57 km Azimuth = 221 Max Amp = 1.15e−04 cm Zcorr = 6 VR = 66 22.50 sec
MW43.data
Distance = 51 km Azimuth = 189 Max Amp = 1.60e−04 cm Zcorr = 5 VR = 53 22.50 sec
LN15.data
Distance = 23 km Azimuth = 54 Max Amp = 3.11e−04 cm Zcorr = 0 VR = 23 22.50 sec
LL24.data
Distance = 58 km Azimuth = 336 Max Amp = 1.71e−04 cm Zcorr = 4 VR = 85 22.50 sec
�
page 1 of 2
Tangential Radial Vertical
NG55.data
Distance = 60 km Azimuth = 217 Max Amp = 2.34e−04 cm Zcorr = 6 VR = 57 22.50 sec
NG54.data
Distance = 72 km Azimuth = 268 Max Amp = 8.06e−05 cm Zcorr = 6 VR = 50 22.50 sec
LN26.data
Distance = 18 km Azimuth = 307 Max Amp = 2.29e−04 cm Zcorr = 2 VR = 34 22.50 sec
LN25.data
Distance = 27 km Azimuth = 329 Max Amp = 1.95e−04 cm Zcorr = 3 VR = 39 22.50 sec
LN15.data
Distance = 21 km Azimuth = 65 Max Amp = 2.16e−04 cm Zcorr = 0 VR = 29 22.50 sec
LN14.data
Distance = 54 km Azimuth = 56 Max Amp = 7.62e−05 cm Zcorr = 6 VR = 76 22.50 sec
�
page 1 of 2
Tangential Radial Vertical
LN34.data
22.50 sec
LL65.data
22.50 sec
�
page 2 of 2
Tangential Radial Vertical
PR52.data
22.50 sec
PR61.data
22.50 sec
�
page 2 of 2
Tangential Radial Vertical
THAN.data
Distance = 163 km Azimuth = 168 Max Amp = 5.74e−03 cm Zcorr = 14 VR = 28 30.00 sec
MLOW.data
Distance = 91 km Azimuth = 156 Max Amp = 1.01e−02 cm Zcorr = 6 VR = 58 30.00 sec
ZINI.data
Distance = 168 km Azimuth = 107 Max Amp = 1.18e−02 cm Zcorr = 11 VR = 75 30.00 sec
NGEA.data
Distance = 211 km Azimuth = 110 Max Amp = 1.42e−02 cm Zcorr = 17 VR = 44 30.00 sec
LIGA.data
Distance = 168 km Azimuth = 116 Max Amp = 9.85e−03 cm Zcorr = 12 VR = 75 30.00 sec
KURU.data
Distance = 217 km Azimuth = 127 Max Amp = 1.08e−02 cm Zcorr = 19 VR = 58 30.00 sec