William Foxall

Partitioning of Seismoacoustic Energy and Estimation of Yield and Height‐of‐Burst/Depth‐of‐Burial for Near‐Surface Explosions

Explosions near the Earths surface excite both seismic ground motions and atmospheric overpressure. The energy transferred to the ground and atmosphere from a near-surface explosion depends on yield (W) as well as the height-of-burst/ depth-of-burial(HOB/DOB)forabove/belowgroundemplacements.Wereportanalyses of seismic and overpressure motions from the Humble Redwood series of low-yield, near-surface chemical explosions with the aim of developing quantitative models of energy partitioning and a methodology to estimate W and HOB/DOB. The effects of yield, HOB, and range on amplitudes can be cast into separable functions of range andHOBscaledbyyield.WefindthatdisplacementoftheinitialPwaveandtheintegral of the positive overpressure (impulse) are diagnostic of W and HOB with minimal scat- ter. An empirical model describing the dependence of seismic and air-blast measure- ments on W, HOB/DOB, and range is determined and model parameters are found by regression. We find seismic amplitudes for explosions of a given yield emplaced at or above the surface are reduced by a factor of 3 relative to fully contained explosions below ground. Air-blast overpressure is reduced more dramatically, with impulse reduced by a factor of 100 for deeply buried explosions relative to surface blasts. Oursignalmodelsare usedtoinvertseismicandoverpressure measurementsforW and HOB and we find good agreement (W errors <30%, HOB within meters) with ground- truth values for four noncircular validation tests. Although there is a trade-off between W and HOB for a single seismic or overpressure measurement, the use of both meas- urement types allows us tolargelybreak this trade-off and better constrainW and HOB. However, both models lack resolution of HOB for aboveground explosions.

Concept for a High MEO InSAR Seismic Monitoring System

Demonstration of a spaceborne system to image seismic surface waves dynamically (i.e. coseismically) would be the early steps of a future operational capability for monitoring earthquakes and discriminating clandestine underground nuclear tests. Complementing the global network of seismic instruments, such system would enable unprecedented global mapping of the velocity structure of the Earths crust, thereby improving hypocentral location, understanding of rupture dynamics and wave propagation effects, and source characterization. Seismic wave measurement requirements include lower bounds on detectability of events and wave amplitude accuracy for different levels of analysis, such as source characterization and crustal tomography, with 10-100 mum wave amplitude resolution for waves nominally traveling 5 km/s, an upper frequency bound based on earthquake surface displacement spectra, and minimum horizontal resolution (1-5 km) and areal coverage. Advanced radar technologies are keys to demonstrating a pre-operational system leading to a high MEO (10,400 km orbit altitude) constellation for continuous surveillance.

Suborbital and Spaceborne Monitoring of Seismic Surface Waves

The development of a suborbital or spaceborne system to monitor seismic surface waves poses an intriguing prospect for advancing the state of seismology. This capability would enable an unprecedented global mapping of the velocity structure of the Earths crust, event source location and characterization, and greatly improved understanding of earthquake rupture dynamics and wave propagation effects. Seismic wave measurement requirements include lower bounds on detectability of earthquakes and wave amplitude accuracy for different levels of analysis, such as source characterization and crustal tomography, with 10-100 mum wave amplitude resolution for waves nominally traveling 5 km/s, an upper frequency bound based on earthquake surface displacement spectra, and minimum horizontal resolution (1-5 km) and aerial coverage. The technological challenges to developing any such system are at this stage enormous. However, preliminary architectural concepts suggest feasibility in a far-term horizon while fostering collaboration on meeting scientific and operational challenges