Automatic and Real-time Processing of Tilt Records for Prediction of Explosions at Semeru Volcano, East Java, Indonesia

Eruptive activity of Semeru Volcano, East Java, Indonesia, is characterized by intermittent occurrence of strombolian and vulcanian types in intervals of 15 – 45 minutes. The explosive eruptions accompany explosion earthquakes and tilt changes of ground around the summit crater. Prior to the explosions (16 – 300 s before), gradual upward tilts of the crater side were detected with amounts of 0.3 – 20 nrad. The upward tilts turned to downward after start of explosive eruptions and tilt decreased by 0.7 – 50 nrad for 30 – 70 s. In order to detect the precursory tilt changes in real time automatically by using the tilt record, software coded by Visual Basic was developed. The software receives UDP packet data from A/D converter for the tiltmeter and shows the record on PC display. The software judge stages of volcanic activity (pre-eruption or eruption) based on the tilt change. In a test, 72% of increase in tilts prior to explosions was successfully detected.