The relative amplitude method(RAM) is more suitable for source inversion of low magnitude earthquakes because it avoids the modeling of short-period waveforms.We introduced an improved relative amplitude method(IRAM) which is more robust in practical cases.The IRAM uses a certain function to quantify the fitness between the observed and the predicted relative amplitudes among direct P wave,surface reflected pP and sP waves for a given focal mechanism.Using the IRAM,we got the fault-plane solutions of two earthquakes of mb4.9 and mb3.8,occurred in Issyk-Kul lake,Kyrgyzstan.For the larger event,its fault-plane solutions are consistent with the Harvard's CMT solutions.As to the smaller one,the strikes of the solution are consistent with those of the main faults near the epicenter.The synthetic long period waveforms and the predicted P wave first motions of the solutions are consistent with observations at some of regional stations.Finally,we demonstrated that fault-solutions cannot interpret the characteristics of teleseismic P waveforms of the underground nuclear explosion detonated in Democratic People's Republic of Korea(DPRK) on October 9,2006.
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