| NSF Org: |
EAR Division Of Earth Sciences |
| Recipient: |
|
| Initial Amendment Date: | August 1, 2013 |
| Latest Amendment Date: | May 12, 2015 |
| Award Number: | 1251954 |
| Award Instrument: | Continuing Grant |
| Program Manager: |
Margaret Benoit
mbenoit@nsf.gov (703)292-7233 EAR Division Of Earth Sciences GEO Directorate for Geosciences |
| Start Date: | September 1, 2013 |
| End Date: | August 31, 2017 (Estimated) |
| Total Intended Award Amount: | $279,748.00 |
| Total Awarded Amount to Date: | $279,748.00 |
| Funds Obligated to Date: |
FY 2015 = $55,346.00 |
| History of Investigator: |
|
| Recipient Sponsored Research Office: |
4333 BROOKLYN AVE NE SEATTLE WA US 98195-1016 (206)543-4043 |
| Sponsor Congressional District: |
|
| Primary Place of Performance: |
Seattle WA US 98195-1310 |
| Primary Place of
Performance Congressional District: |
|
| Unique Entity Identifier (UEI): |
|
| Parent UEI: |
|
| NSF Program(s): | EARTHSCOPE-SCIENCE UTILIZATION |
| Primary Program Source: |
01001314DB NSF RESEARCH & RELATED ACTIVIT |
| Program Reference Code(s): |
|
| Program Element Code(s): |
|
| Award Agency Code: | 4900 |
| Fund Agency Code: | 4900 |
| Assistance Listing Number(s): | 47.050 |
ABSTRACT
Slow slip events and non-volcanic tremor provide new insight into the mode of strain release along the deep extension of faults. These events are noteworthy for their long durations (~days) and large magnitudes (~M6). We have yet to fully understand what properties or conditions on the plate interface act to prevent the rapid slip that is typically observed with earthquakes. Slow slip and tremor also constrain the lower edge of the seismogenic zone, a variable that is useful for seismic hazard studies, and event histories are an input into studies that explore the time-dependent loading of stress on the seismogenic zone. Most of the existing geodetic studies of slow slip have focused on observations made by GPS. In this work, we integrate borehole strainmeters with GPS data to more fully characterize the spectrum of slow slip behavior on the Cascadia subduction zone. Time-dependent inversions of GPS and strainmeter time series are performed using the Extended Network Inversion Filter. By incorporating the strainmeters into our analysis, we resolve smaller slow slip events and extract greater information about the propagation characteristics than by using GPS alone. From our expanded catalog of slow slip events, we are extracting the source parameters and testing whether the smaller slow slip events (~M5+) obey the same scaling relationships as has been inferred for the larger ones (~M6+). The strainmeter data also allow us to better compare the spatial and temporal correlation of slow slip and the location of tremor. We are testing the idea of whether tremor marks the leading edge of slow slip or whether tremor is embedded within the slipping zone. Lastly, we are evaluating the up-dip taper of slow slip and seeing if the surface observations are consistent with an abrupt up-dip edge, as suggested by the tremor. Our analysis of the strainmeter data allows us to better evaluate the calibration and noise characteristic of the strainmeter time series. We will specifically use the GPS-derived slip models to independently validate the strainmeter calibrations.
PROJECT OUTCOMES REPORT
Disclaimer
This Project Outcomes Report for the General Public is displayed verbatim as submitted by the Principal Investigator (PI) for this award. Any opinions, findings, and conclusions or recommendations expressed in this Report are those of the PI and do not necessarily reflect the views of the National Science Foundation; NSF has not approved or endorsed its content.
Subduction zone earthquakes are responsible for some of the largest natural disasters on our planet when they occur near populated areas. These earthquakes occur on a gently dipping fault that outcrops on the ocean floor, extends under the coastline, and continues to great depth in the earth. However, the source area on the fault where these earthquakes nucleate is impossible to access, making it difficult to infer the properties of the fault near the base of the earth’s crust. However, a new class of faulting behavior, referred to as Episodic Tremor and Slip (ETS) has afforded scientists a new window into the seismic activity on the deep extent of these fault zones. ETS are enigmatic faulting episodes where transient fault movement is accompanied by subtle tremor signals. They occur throughout Cascadia, along a north-south band that passes beneath the I-5 corridor. While not easily felt on the surface, these events occur frequently (about once a year at any location), and release the energy equivalent to a magnitude 6.5 earthquake spread out over a couple weeks.
In this work, we have sharpened our focus of ETS events on the Cascadia subduction zone. In particular, we have investigated where, in detail, tremor and slow slip are coincident, and where the tremor component is turned off. We have generated spatial maps of the slip amplitude for 11 ETS events that indicate the magnitude and reveal their spatial pattern. A key result from our work is a careful assessment of where tremor and slip map both along-strike and down-dip. While estimates of tremor activity and the magnitude of aseismic slip on the fault generally correlate, there are distinct variations in behavior. These variations likely correlate to where fault properties vary across the fault, as we transition from seismic behavior (source area of shaking), to transient slow slip (no discernable shaking), and tremor plus slow slip (only small, imperceptible shaking). One fault property that is a leading candidate is the presence pore fluid on the fault, which likely varies systematically with depth, and acts to change the stability condition. Our work also improved how GPS, tremor catalogs, and strainmeter observations are integrated to provide a more refined image of ETS behavior.
This project funded the training of an undergraduate intern, 3 graduate students who are pursing PhDs, and a postdoc, all of whom gained new professional skills in data analysis, critical thinking, communication, and modeling. The undergraduate intern participated on the research project through the RESESS program, an internship program that seeks to prepare underrepresented minorities for a future in graduate school.
Last Modified: 01/30/2018
Modified by: David A Schmidt
Please report errors in award information by writing to: awardsearch@nsf.gov.
