Experts say the tectonic quakes that recently struck Java and Sumatra might be responsible for triggering increased activities at several volcanoes on both islands.

A seismologist from the Bandung Institute of Technology (ITB), Nanang T. Puspito, said the tectonic quakes that occurred along the West Sumatra and southern Java coasts over the past week have likely increased activity in a number of volcanoes.

Nanang said plate movements below the earth's mantle could increase the pressure of the upper magma pocket of a volcano and trigger an eruption followed by volcanic quakes.

Another ITB seismologist, Wahyu Triyono, however, said the correlation between increased volcanic activity and quakes resulting from the thrust between the Indo-Australian and Eurasian plates must be further analyzed.

"Apparently, there is a connection, but we need to reevaluate the intensity of the impact," Wahyu told The Jakarta Post in Bandung.

Nanang said magma pockets might be affected by increased pressure below the earth's mantle and trigger activity in volcanoes.

"The release of energy is usually marked by rising energy in certain sections of the earth's surface. We have to analyze the impact and duration of energy transfer," said Nanang, who heads the Seismotectonic Laboratory at ITB's Geophysics and Meteorological School.

However, head of the Bandung-based Volcanology and Geology Disaster Mitigation Center, Surono, rejected the idea, saying the rise in activity is in line with the volcanoes' eruption patterns.

Surono said based on observations, the volcanic activity of Mount Anak Krakatau, for instance, coincided with its eruption pattern of around four-year intervals.

He said tectonic quakes occurred far below the earth's surface and had no impact on current volcanic activities, adding activity at Mount Kelud also coincided with its eruption cycle, after last erupting in 1990.

"It's a different process, so there's no correlation."

Head of the center's observation division, Agus Budiarto, said a tectonic quake was characterized by three effects; plug magma discharge, delay effects and agitate the pressure of magma pockets.

Agus said the subduction zone system of each volcano was different.

"Anak Krakatau's alert status has long been determined but it has only now shown signs of activity. It's a relatively young volcano, which is still in its formative period, so it's quite active," said Agus.

Anak Krakatau, which is currently on the second-highest alert status, has shown increased signs of volcanic activity.

On Monday, it erupted 58 times, triggered 16 deep volcanic quakes and 22 shallow volcanic quakes.

On Sunday, 68 deep volcanic tremors were recorded and 236 eruptions, prompting authorities to set Anak Krakatau's alert status as cautious, similar to that of Mount Soputan in North Sulawesi.

Mount Soputan and Mount Karangetan, both in North Sulawesi, are on the same alert status as Anak Krakatau.

Meanwhile, Mount Kelud in East Java is on top-alert status, meaning an eruption is imminent.

There are nine volcanoes in the country on the third-highest alert status: Mount Kerinci in Jambi province; Mount Gamkonora on Halmahera Island in Maluku; Mount Dukono and Mount Ibu in North Maku; Mount Merapi in Yogyakarta; Mount Semeru in East Java; Mount Talang in Solok regency, West Sumatra; Mount Lokon in North Sulawesi; and Mount Papandayan in Garut, West Java.