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Faulting Processes During Early-Stage Rifting: RAMP Response to the 2009-2010 Northern Malawi Earthquake Sequence James Gaherty (Lamont-Doherty Earth Observatory of Columbia University), Donna Shillington (Lamont-Doherty Earth Observatory of Columbia University), Scott Nooner (Lamont-Doherty Earth Observatory of Columbia University), Cindy Ebinger (University of Rochester), Andy Nyblade (Pennsylvania State University) On December 6, 2009, an unusual sequence of earthquakes began in the Karonga region in northern Malawi (Fig. 1). The sequence initiated with an Mw 5.8 event, which was followed 32 hours later by an Mw 5.9 event, and then nearly 12 days later by an Mw 6.0 event. Within this time span there were an additional six Mw > 5 events, with many more events that were at or below the threshold of the NEIC location system. Such events are very rare in the Malawi portion of the East African rift (EAR); prior to this sequence, the NEIC catalog [which dates to, 1973] contains only three events of M > 5 within the rift valley between 9-12ºS latitude. This contrasts with both the Western and Eastern branches of the EAR through Kenya and Tanzania, which between them have experienced 115 M > 5 events in the same time period. Nearly all other moderate-size earthquakes within the Western Rift appear to be on major border faults, but the locations, mechanisms and event depths of the Karonga events imply that they occurred due to slip on normal faults within the hanging wall block. They offer a rare opportunity to evaluate how early-stage rifting is accommodated within the hanging wall of the system. The December 2009 earthquake sequence resulted in four casualties, 300 injuries and thousands of displaced people. Malawi currently has very limited capacity to monitor and locate such earthquakes; they have no permanent national network. With the support of IRIS PASSCAL, we undertook a Rapid Array Mobilization Program (RAMP) deployment at the request of the Director of the Malawi Geological Survey Department (MGSD). We deployed six broadband stations for a fourmonth period to monitoring aftershock activity. We recorded several thousand local events, and analysis is ongoing. This technical response complimented the post-event aid that was being provided by NGO’s and government agencies. Through our field activities, we explained the earthquakes to teachers, police officers and villagers. We provided television and radio interviews about earthquakes and the necessity of seismic monitoring, and blogged about our undertaking (http://blogs.ei.columbia.edu/ blog/tag/east-africa-rift/). We trained personnel from the MGSD in seismic equipment and field methods. This effort directly resulted in the purchase of equipment by the MGSD for 9 stations to begin a seismic network in Malawi; they purchased the same equipment employed in our RAMP deployment. References 33˚36' 33˚42' 33˚48' 33˚54' 34˚00' 34˚06' -9˚42' Biggs, J., E. Nissen, T. Craig, J. Jackson, and D. P. Robinson (2010), Breaking up the hanging wall of a rift-border fault: the 2009 Karonga Earthquakes, Malawi, Geophys. Res. Lett., 37, doi:10.1029/2010GL043179. Acknowledgements: Funding for the RAMP deployment was provided by Columbia University through the Lamont-Doherty Earth Observatory and the Earth Institute. The IRIS PASSCAL program provided the instruments, as well as financial support for shipping. Data collection and instrument recovery supported by the NSF RAPID grant EAR-1019379. -9˚48' -9˚54' -10˚00' -10˚06' -10˚12' -10˚18' 0 km 10 Seismic stations Karonga Fault CLIN 19 Dec 2009 Locations of earthquakes with M>4.5 between Dec 8-21 from from USGS LUGH 6.0 POLI 8 Dec 2009 5.9 AIR 6 Dec 2009 ARCH 5.8 LAKE MALAWI Karonga SCH Figure 1. Locations of main events from NEIC catalogue (red stars), seismic stations in RAMP deployment (white squares and text) and a subset of faults onshore (black and grey lines) and offshore (grey dotted lines). Purple dotted line indicates interpreted fault of Biggs et al. (2010) based on InSAR data. II-108 | 2010 IRIS Core Programs Proposal | Volume II | Fault Structure
Structure of the California Coast Ranges and San Andreas Fault at Safod from Seismic Waveform Inversion and Reflection Imaging Florian Bleibinhaus (Virginia Tech; now at Salzburg Univ.), John A. Hole (Virginia Tech), Trond Ryberg (GeoForschungsZentrum, Potsdam), Gary S. Fuis (U. S. Geological Survey, Menlo Park) A seismic reflection and refraction survey across the San Andreas Fault (SAF) near Parkfield provides a detailed characterization of crustal structure across the location of the San Andreas Fault Observatory at Depth (SAFOD). Steep-dip prestack migration and frequency domain acoustic waveform tomography were applied to obtain highly resolved images of the upper 5 km of the crust for 15 km on either side of the SAF. The resulting velocity model constrains the top of the Salinian granite with great detail. Steep-dip reflection seismic images show several strong-amplitude vertical reflectors in the uppermost crust near SAFOD that define a 2-km-wide zone comprising the main SAF and two or more local faults. Another prominent subvertical reflector at 2–4 km depth 9 km to the northeast of the SAF marks the boundary between the Franciscan terrane and the Great Valley Sequence. A deep seismic section of low resolution shows several reflectors in the Salinian crust west of the SAF. Two horizontal reflectors around 10 km depth correlate with strains of seismicity observed along-strike of the SAF. They represent midcrustal shear zones partially decoupling the ductile lower crust from the brittle upper crust. The deepest reflections from 25 km depth are interpreted as the crustmantle boundary. Waveform inversion velocity model using 3.2 to 14.4 Hz data. A thick black line marks the SAFOD main hole. Contour lines are annotated in kilometers per second. Steep-dip prestack depth migrated image. The shots used to produce the image are indicated on top. The section was normalized for subsurface coverage. References Bleibinhaus, F., J. A. Hole, T. Ryberg, and G. S. Fuis (2007), Structure of the California Coast Ranges and San Andreas Fault at SAFOD from seismic waveform inversion and reflection imaging, J. Geophys. Res., 112, B06315. Manual line drawing of the major reflectors from the steep-dip migration (thick white lines) overlaid onto the final waveform tomography velocity model. The top of the Salinian granite, as inferred from the 5 km/s contour, is marked by a thin white line. Local earthquake hypocenters (white circles) constrain the position of the SAF at depth. Solid black lines are interpretation. The surface positions of faults are: BCF, Buzzard Canyon; SAF, San Andreas; GHF, Gold Hill; WCF, Waltham Canyon. Acknowledgements: This work was funded by U.S. National Science Foundation grant EAR-0106534. The data collection was supported by NSF, the Deutsche Forschungsgemeinschaft, the GeoForschungsZentrum Potsdam, and the U.S. Geological Survey. 2010 IRIS Core Programs Proposal | Volume II | Fault Structure | II-109
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volume ii - accomplishments Facilit
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volume ii - accomplishments Facilit
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CONTENTS Introduction..............
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Non-Volcanic Tremor along the Oaxac
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Detecting the Limit of Slab Break-o
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Lower Mantle, Core-Mantle Boundary
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• Non-Earthquake Seismic Sources
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acoustics community by permitting a
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Near-Surface Environments - Hazards
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Why Do Faults Slip? Emily Brodsky (
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Another probe of fault evolution is
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to provide a best match with the Gl
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tectonic disruption and mass accumu
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W3 ∆ 5 . A number of intriguing r
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thermal and compositional effects r
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Towards a Global School Seismic Net
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On-Line Seismology Curriculum for U
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Teachers on the Leading Edge: Earth
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USArray Education and Outreach in S
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From an IRIS Lecture Tour to a Gene
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Explorer Series Robert Bartolotta (
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Workshop “Earth System Science fo
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The IRIS Internship Cycle: From Int
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Community-Outreach Efforts in Data
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Site Reconnaissance for Earthscope
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jAmaseis: Seismology Software Meeti
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Near Real-Time Simulations of Globa
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FuncLab: A MATLAB Interactive Toolb
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Five Years of Distributing the Seis
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IRIS DMS Data Products, Beyond Raw
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Local Earthquakes in the Dallas-Ft.
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Epicentral Location Based on Raylei
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Analysis of Spatial and Temporal Se
Page 69 and 70: Exceptional Ground Motions from the
Page 71 and 72: The 2010 Mw7.2 El Mayor-Cucapah Ear
Page 73 and 74: Effects of Kinematic Constraints on
Page 75 and 76: Imaging of the Source Properties of
Page 77 and 78: Teleseismic Inversion for Rupture P
Page 79 and 80: The Global Aftershocks of the 2004
Page 81 and 82: The 17 July 2006 Java Tsunami Earth
Page 83 and 84: Seismic Cycles on Oceanic Transform
Page 85 and 86: Migration of Early Aftershocks Foll
Page 87 and 88: Apparent Stress Variations at the O
Page 89 and 90: Automated Identification of Telesei
Page 91 and 92: Evaluating Ground Motion Prediction
Page 93 and 94: Tremor Monitoring Aaron Wech (Unive
Page 95 and 96: Slow Slip and Tremor in the Norther
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Page 99 and 100: Intimate Details of Tremor Observed
Page 101 and 102: Global Search of Triggered Tremor a
Page 103 and 104: Slab Morphology in the Cascadia For
Page 105 and 106: Source Analysis of the Memorial Day
Page 107 and 108: Iceberg Tremor and Ocean Signals Ob
Page 109 and 110: Elucidating the Stick-Slip Nature o
Page 111 and 112: Probing the Atmosphere and Atmosphe
Page 113 and 114: Volcanic Plume Height Measured by S
Page 115 and 116: Eruption Dynamics at Mount St. Hele
Page 117 and 118: A Search for the Lunar Core Using A
Page 119: Seismic Imaging of the Mt. Rose Fau
Page 123 and 124: Temporal Variations in Crustal Scat
Page 125 and 126: High-Resolution Locations of Trigge
Page 127 and 128: Adjoint Tomography of the Southern
Page 129 and 130: Crustal Structure of the High Lava
Page 131 and 132: Controlled Source Seismic Experimen
Page 133 and 134: Structural Interpretations Based on
Page 135 and 136: Optimized Velocities and Prestack D
Page 137 and 138: 40 Crustal Structure beneath the Hi
Page 139 and 140: Controlled-Source Seismic Investiga
Page 141 and 142: Northward Thinning of Tibetan Crust
Page 143 and 144: An Integrated Analysis of an Ancien
Page 145 and 146: Crustal Velocity Structure of Turke
Page 147 and 148: Ambient Noise Tomography of the Pam
Page 149 and 150: Ambient Noise Monitoring of Seismic
Page 151 and 152: Mushy Magma beneath Yellowstone Ris
Page 153 and 154: Imaging the Seattle Basin to Improv
Page 155 and 156: Developing a Database of ENA Ground
Page 157 and 158: Lithospheric Layering in the North
Page 159 and 160: eflective zones on depthmigrated se
Page 161 and 162: FischerFig05.pdf 1 2/8/10 12:31 PM
Page 163 and 164: S-Velocity Structure of Cratons, fr
Page 165 and 166: Seismic Structure of the Crust and
Page 167 and 168: Subducted Oceanic Asthenosphere and
Page 169 and 170: Detecting the Limit of Slab Break-o
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Pn Tomography of the Western United
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3-D Isotropic Shear Velocity Model
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Seismic Anisotropy Associated with
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Anisotropy in the Great Basin from
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Source-Side Shear Wave Splitting an
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S-Velocity Structure of the Upper M
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Velocity Structure of the Western U
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Segmented African Lithosphere benea
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Imaging the Mantle Wedge in the Cen
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A Slab Remnant beneath the Gulf of
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Imaging the Southern Alaska Subduct
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Opposing Slabs under Northern South
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Effect of Prior Petrological Constr
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Global Azimuthal Seismic Anisotropy
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The Stratification of Seismic Azimu
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Upper Mantle Anisotropy beneath the
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The Teleseismic Signature of Fossil
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Seismic Anisotropy under Central Al
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Stress-Induced Upper Crustal Anisot
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Tau-p Depropagation of Five Regiona
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Mapping the Upper Mantle with the S
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Upper Mantle Structure of Southern
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The Africa-Europe Plate Boundary in
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The Isabella Anomaly Imaged by Eart
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Tomographic Image of the Crust and
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Small-Scale Mantle Heterogeneity an
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Mantle Heterogeneity West and East
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New Geophysical Insight into the Or
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The Plume-slab Interaction beneath
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Imaging the Shear Wave Velocity "Pl
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Slab Fragmentation and Edge Flow: I
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Mantle Shear-Wave Velocity Structur
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Discordant Contrasts of P- and S-Wa
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Upper Mantle Discontinuity Topograp
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Edge-Driven Convection beneath the
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Imaging Attenuation in the Upper Ma
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Three-Dimensional Electrical Conduc
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Core-Mantle Boundary Heat Flow Thor
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Constraints on Lowermost Mantle Ani
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Localized Double-Array Stacking Ana
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Waveform Modeling of D" Discontinui
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Absence of Ultra-Low Velocity Zones
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Moving Seismic Tomography Beyond Fa
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A Three-Dimensional Radially Anisot
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The Importance of Crustal Correctio
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Slabs Do Not Go Gentle Karin Sigloc
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Localized Temporal Change of the Ea
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Core Structure Reexamined Using New
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Large Variations in Travel Times of
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Observations of Antipodal PKIIKP Wa
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Regional Variation of Inner Core An
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Wide-Scale Detection of Earthquake
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