Conventional Procedure:Measure magnitudeassume a magnitude-yield equation

Yield Estimation for North Korean Tests

Problem: Source medium, burial depth,mantle attenuation under testsite affect magnitude-yield equation

Goal: Apply a method that accounts for source medium and burial depth effects,eliminates attenuation. Precise relative yields obtained. Still need to model forabsolute calibration.

NTS: mb = 3.94 + 0.81 log (yield)Semi: mb = 4.45 + 0.75 log (yield)For September 3, 2017 event mbNEIC = 6.3Yield(NTS) = 820 kt; Yield(Semi) = 293 kt

September 3, 2017Mt. MantapN. Korean Nuclear TestSite (viewed from south)

2016-2017Events maybe beneathpeak topography,about 780 mhigher than tunnelentrance

North Tunnel entrance

We can model the P wave motions well, for particular yield – burial depth – attenuationcombinations

t* 0.5 s t* 0.75 s t* 1.0s

2017 Findings for Absolute Yield Modeling for 2017, with Delayed pP

Direct modeling of teleseismic P waves for 2017indicates yield of 220 ± 80 kt, for H 750 m, andpP delay time factor of 2.25.

• Using the 2017 modeling to set

• the absolute scale for all events

• Intercorrelations give:

• 2017 220 ± 80 kt, 750 m (fixed)

• 2016b 17.0 ± 5 kt, 750-610 m

• 2016a 9.9 ± 3 kt, 750-540 m

• 2013 14.0 ± 5 kt, 310-540 m

• 2009 4.5 ± 2 kt, 550-520 m

• 2006 1.5± 0.5 kt, 400-280 m

Relative yieldestimates Areconsistent forthe 5 smallerevents, lessstable relativeto 2017.