wɪð ɐ sˈaɪzməɡɹˌæf ðeɪ dɪtˈɜːmɪn ðætðə ɹˈʌmbəlz ɑːɹ dˈuː tə sˌʌm kˈaɪnd ʌv sˈɜːfɪs æktˈɪvᵻɾi, nˌɑːt dˈiːp ˈɜːθkweɪks.
With a seismograph they determine that the rumbles are due to some kind of surface activity, not deep earthquakes.