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Kelud volcano is located in the Kediri sub-district, East Java Province, Indonesia. This volcano is still active, with total population, in the radius of 10 km, is around 10 thousand people. Kelud volcano is a popular tourist destination. On the weekend, total visitor can reach 5,000 people per-day. These people are at high risk when the Kelud volcano erupts. The last eruption of the Kelud volcano occurred in 2014 and was explosive eruption. Previously, there was an effusive eruption in 2007. These two types of eruption have its own geo hazard risk. Thus, predict the eruption type could help hazard mitigation. In this study, two data sets of earthquakes, 1990-2007 and 2008-2020, were analysed to determine the b-value and its relationship to the eruption type of the Kelud volcano. The calculation of the b-value uses the Gutenberg-Richter relationship. Calculation of the b-value in 2007, when there was an effusive eruption, showed a value of 2.27, while in 2014 (when there was an explosive eruption) was 1.85. After 2009, the curve of the b-value against time shows decrease. As a long term precursor of the Kelud activity, this b-value curve should be analysed continuously, besides volcano tectonic seismicity monitoring.

The complexity of a system recorded in time series data can be measured statistically using permutation entropy (PE). The state of a system (e.g. regular, chaotic, random, etc.) that underlies the appearance of variations in time series can be determined with PE. Since volcanoes are considered as the complex dynamical system controlled by interactions of many processes. Permutation entropy can be applied to study the system mechanism of volcano. We utilized PE to study system mechanism of Kelud volcano in 2007 dome-forming eruption period, from 3 (KWH; KLD; UMBK) seismic stations with different distances from the crater lake. Then, we want to compare the results. The result of study shows that the PE pattern for each station is different. The unique PE pattern that can be used as an eruption precursor is only shown at KWH and KLD stations. This pattern began to appear 2.7 days before the eruption on 3 November 2007. Data from UMBK station doesn’t show unique PE pattern. The factors such as sensor distance from magmatic activity center, size, and type of eruption probably influenced the final PE result. Using PE as the addition to volcano monitoring can maximize efforts in mitigation activities.