Complex sentence: At around 23:30 (15:30 UTC), the first explosion occurred and registered as a magnitude 2.3 earthquake, generating seismic shock-waves energetically equivalent to 3 tonnes of TNT.
Split into simpler sentences: At around 23:30 (15:30 UTC), the first explosion occurred and registered as a magnitude 2.3 earthquake. Initial reports estimate that the first explosion was equivalent to 3 tonnes of TNT.