Determining SAFOD area microearthquake locations solely with the Pilot Hole seismic array data

Abstract

[1] In August 2002, an array of 32 three-component geophones was installed in the San Andreas Fault Observatory at Depth (SAFOD) Pilot Hole (PH) at Parkfield, CA. As an independent test of surfaceobservation-based microearthquake locations, we have located such events using only data recorded on the PH array. We then compared these locations with locations from a combined set of PH and Parkfield High Resolution Seismic Network (HRSN) observations. We determined the uncertainties in the locations as they relate to errors in the travel time picks and the velocity model by the bootstrap method. Based on the PH and combined locations, we find that the ''C2'' cluster to the northeast of the PH has the smallest location uncertainties. Events in this cluster also have the most similar waveforms and largest magnitudes. This confirms earlier suggestions that the C2 cluster is a promising target for the SAFOD Main Hole.

Analysis of induced seismicity in geothermal reservoirs – An overview

“…This is primarily due to the shorter distances between the sensors and the event locations, and to avoiding the heterogeneous and attenuating near surface layers, as well as to the improved signal-to-noise ratio from being below the surface. This results in reduced amplitude losses from geometrical spreading and intrinsic and scattering attenuation, as observed when comparing data from deep borehole with surface seismic data (Oye et al, 2004). Near-surface low-Q sedimentary layers (see Table 1, Groß Schönebeck), are particularly detrimental to the recorded signal quality, especially for -wave arrivals (Oye et al, 2010).…”

The SAFOD Pilot Hole seismic array: Wave propagation effects as a function of sensor depth and source location

“…Earthquake data recorded on these instruments carries the benefit of high signal‐to‐noise ratios even for small events. The PH data alone can be used to find their locations [ Oye et al , 2004]. Further, the multiple levels and overall lengths of the array provide important information about the velocity structure both in the vicinity of the PH and along the SAF.…”

“…These data have much higher signal‐to‐noise ratios than observations made on the surface [e.g., Abercrombie , 1997] and hence give very accurate measurements of travel times and incidence angles with depth along the array. Combined, these data by themselves have helped constrain the locations of “target earthquakes” for the SAFOD drilling effort [ Oye et al , 2004], including two M ∼ 2 events in October 2003 that are currently under intense investigation for just this purpose. Data from surface networks and PH recordings have been used for event location and determination of the 3‐D velocity structure at the SAFOD site [ Thurber et al , 2004; Roecker et al , 2004].…”

Observation and scaling of microearthquakes from the Taiwan Chelungpu-fault borehole seismometers

“…The forth one is located at the depth of 1110.28 m, close to the identified major slip zone (Ma et al 2006) with coseismic slip of about 12 m. In addition, a surface short period seismic network with 10 stations was deployed in a radius of about 5 km around TCDP drill site between 2006 August and 2007 September, to better constrain microearthquake locations. Borehole installations with linear array configuration have been used to investigate seismically active fault zones (Daley & McEvilly 1990; Abercrombie 1995; Nishigami et al 2001; Oye et al 2004; Oye & Ellsworth 2005). Most of these studies, determined accurate microearthquake locations by combining surface network and borehole array records and thereby identified the seismic activity within the fault zone (Jost et al 1998; Tadokoro et al 2000; Thurber et al 2003; Ake et al 2005).…”