Update 11:53 UTC : This earthquake was triggered by compression forces as can be seen in the mechanism below
Image courtesy USGS
Update 08:35 UTC : The least we can say is that the interaction in between the Indo-Australian plate and the Eurasian plate is very active at the moment. 3 strong to very strong earthquakes in a matter of 1 week and at different locations and different depths. What next ? Seismologists all over the world are trying to find patterns, clues who can at last a grain of hope in predicting the next strong one. But unfortunately … no generally accepted conclusive solution as far as we know.
Update 08:29 UTC : The lower map shows a 1916 M7.3 earthquake a little to the south. Interesting to notice that also that earthquake was at a depth of 100 km.
Update 08:14 UTC : The quake was felt for about 3 to 5 seconds on the nearby coast. At the time of writing this update only a couple of reports are mentioning some minor damage to a limited number of houses. There was never a risk for a tsunami.
Below the Geofon seismogram recorded at Jajag, Java. The big blue amplitude is this earthquake, the Red ones are the New Ireland and New Britain massive earthquakes who are visible on seismograms all over the world.
Seismogram courtesy Geofon Germany
The strongest shaking was felt at the south-eastern part of Java. The earthquake itself was felt in Java, Bali and even Lombok. The main reason for the shaking is the depth of the hypocenter (breaking point inside the earth). If deeper, this weakens the shaking but at the same time increases the radius where the quake was felt.
Hazard map assessment of Mount Merapi, Central Java, Indonesia using remote sensing
Last update: January 11, 2012 at 1:37 pm by By Armand Vervaeck
Author : David Harris, IGES department, Aberystwyth University, Wales
Abstract
As the global population is predicted to reach 7 billion people by 2012, land pressures and rapid population growth is resulting in many more communities living within danger zones of natural hazards, a pattern particularly seen around volcanoes. This thesis will emphasise the impact of volcanoes on populations using the example of Mount Merapi, Indonesia. Mount Merapi is the most active volcano in Java and has persistent minor eruptions, but according to volcanologists Mount Merapi is heavily overdue a large-scale eruption which could potentially put over 1.1 million people at risk. This thesis begins with a review of published papers and a description of Mount Merapi’s geological history, with a particular focus on its recent eruptions. To better assess Mount Merapi’s threat to the communities that are in close proximity to the summit the thesis uses GIS software to produce a risk map. The risk map is then used as a basis for further analysis on the potential impact in the event of a major eruption. The thesis specifically examines the risk on the basis of current population (e.g. Kemiren, a town with 103,777 people at a risk value site of 10.5) and social vulnerability (e.g. Ngablak, which has a Social Vulnerability Index value of 0.5 – 1.5 and a risk value varying between 7.5 and 28.5). Lastly, the thesis considers the impact of Merapi’s most recent eruptions in October and November 2010 and recommends some considerations for the future in terms of risk reduction by changes in response times and evacuation procedures.
Active volcanoes in the world from 24/08/2011 to 30/08/2011
Last update: September 1, 2011 at 9:43 am by By Armand Vervaeck
New Activity, Unrest or activity change
BAGANA Bougainville (Papua New Guinea) – Satellite map – summit elev. 1750 m
Based on analyses of satellite imagery, the Darwin VAAC reported that on 23 August an ash plume from Bagana rose to an altitude of 3 km (10,000 ft) a.s.l. and drifted 93 km SW. Volcano Information : Bagana volcano, occupying a remote portion of central Bougainville Island, is one of Melanesia’s youngest and most active volcanoes. Bagana is a massive symmetrical lava cone largely constructed by an accumulation of viscous andesitic lava flows. The entire lava cone could have been constructed in about 300 years at its present rate of lava production. Eruptive activity at Bagana is characterized by non-explosive effusion of viscous lava that maintains a small lava dome in the summit crater, although explosive activity occasionally producing pyroclastic flows also occurs. Lava flows form dramatic, freshly preserved tongue-shaped lobes up to 50-m-thick with prominent levees that descend the volcano’s flanks on all sides.
RANAKAH Flores Island (Indonesia) – Satellite map – summit elev. 2350 m
CVGHM reported that observers of Anak Ranakah, a lava dome that formed in 1987 at the base of the large older lava dome of Ranakah, noted white plumes rising up to 10 m high during January-24 August. Seismicity initially increased in December 2010, but increased again during June-August. Based on visual observations and seismic data analyses, CVGHM raised the Alert Level to 2 (on a scale of 1-4). Volcano Information : A new lava dome, named Anak Ranakah (Child of Ranakah) was formed in 1987 in an area without previous historical eruptions at the base of the large older lava dome of Gunung Ranakah. An arcuate group of lava domes extending westward from Gunung Ranakah occurs on the outer flanks of the poorly known Poco Leok caldera on western Flores Island. Pocok Mandosawa lava dome, at 2350 m the highest point on the island of Flores, lies west of Anak Ranakah.
TAMBORA Sumbawa Island (Indonesia) – Satellite map – summit elev. 2850 m
Based on visual observation and seismic data, CVGHM reported an increase in activity at Tambora during the previous five months. Ground-based observers at an observation post in Tambora village noted dense white plumes rising 50-75 m above the caldera rimduring April and June, but no plumes during May or July. In August dense white plumes rose 20 m above the caldera rim. Seismicity started to increase in April and continued to increase through August. On 30 August the Alert Level was raised to 2 (on a scale of 1-4). Volcano Information : The massive Tambora stratovolcano forms the entire 60-km-wide Sanggar Peninsula on northern Sumbawa Island. The largely trachybasaltic-to-trachyandesitic volcano grew to about 4000 m elevation before forming a caldera more than 43,000 years ago. Late-Pleistocene lava flows largely filled the early caldera, after which activity changed to dominantly explosive eruptions during the early Holocene. Tambora was the source of history’s largest explosive eruption, in April 1815. Pyroclastic flows reached the sea on all sides of the peninsula, and heavy tephra fall devastated croplands, causing an estimated 60,000 fatalities. The eruption of an estimated more than 150 cu km of tephra formed a 6-km-wide, 1250-m-deep caldera and produced global climatic effects. Minor lava domes and flows have been extruded on the caldera floor at Tambora during the 19th and 20th centuries.
Gunung Tambora picture courtesy Pirata Alado – http://www.panoramio.com/photo/36914449
PAPANDAYAN Western Java (Indonesia) – Satellite map – summit elev. 2665 m
On 26 August CVGHM reported that Papandayan showed minor to no changes in recent seismicity, deformation, geochemistry, and visual observations; therefore the Alert Level remained at 3 (on a scale of 1-4). Seismicity remained high, but stable, and was dominated by shallow volcanic earthquakes. Deformation measurements showed no change, and water temperatures in multiple fumarolic areas and lakes remained relatively unchanged. Sulfur dioxide gas emissions decreased from 8 tons per day on 12 August to 6 tons per day on 23 August. Carbon dioxide in the soil at a 1 m depth in multiple areas did not increase. Visitors and residents were advised not to venture within 2 km of the active crater. Volcano Information : Papandayan is a complex stratovolcano with four large summit craters, the youngest of which was breached to the NE by collapse during a brief eruption in 1772 and contains active fumarole fields. The broad 1.1-km-wide, flat-floored Alun-Alun crater truncates the summit of Papandayan, and Gunung Puntang to the N gives the volcano a twin-peaked appearance. Several episodes of collapse have given the volcano an irregular profile and produced debris avalanches that have impacted lowland areas beyond the volcano. Since its first historical eruption in 1772, in which a catastrophic debris avalanche destroyed 40 villages, only two small phreatic eruptions have occurred from vents in the NE-flank fumarole field, Kawah Mas.
ETNA Sicily (Italy) – Satellite map – summit elev. 3330 m
Sezione di Catania – Osservatorio Etneo reported that nine days after the previous episode, the New SE Crater produced its twelfth paroxysmal eruptive episode of 2011 during the early morning of 29 August. The event was preceded by an explosion at 2252 on 27 August, and a series of ash emissions from the New SE Crater almost 15 hours later. Weak Strombolian activity visible during the evening on 28 August intensified during the night.
At 0115 on 29 August lava overflowed the rim through a breach in the E crater rim and traveled towards the Valle del Bove. Strombolian activity progressively intensified and two vents within the crater emitted pulsating lava fountains up to 100 m high. The lava fountains again increased in height and a dense plume rose a few kilometers above the summit before drifting toward the SSE. At the same time, a small lava flow issued from the area affected by the collapse of a portion of the cone’s ESE flank during the 20 August paroxysm. At 0220 the SE flank of the cone fractured and exposed a line of new eruptive vents down to the base of the cone that produced lava fountains. A broad lava flow fed by the vents descended into the Valle del Bove, somewhat to the S of the lava flow emitted earlier during the episode. The lava fountaining from the vents within the crater turned into ash emission just after 0220, whereas the lowest vent on the new eruptive fracture continued to produce incandescent jets until 0250. Ash emission continued at a diminishing rate until about 0315. Read also : Another beautiful eruption of Mt Etna (Italy) on August 29 2011 + videos Volcano Information : Mount Etna, towering above Catania, Sicily’s second largest city, has one of the world’s longest documented records of historical volcanism, dating back to 1500 BC. Historical lava flows cover much of the surface of this massive basaltic stratovolcano, the highest and most voluminous in Italy. Two styles of eruptive activity typically occur at Etna. Persistent explosive eruptions, sometimes with minor lava emissions, take place from one or more of the three prominent summit craters, the Central Crater, NE Crater, and SE Crater. Flank eruptions, typically with higher effusion rates, occur less frequently and originate from fissures that open progressively downward from near the summit. A period of more intense intermittent explosive eruptions from Etna’s summit craters began in 1995. The active volcano is monitored by the Instituto Nazionale di Geofisica e Volcanologia (INGV) in Catania.
KILAUEA Hawaii (USA) – satellite map – summit elev. 1222 m
During 24-30 August, HVO reported that the level of the lava-lake surface in the deep pit within Kilauea’s Halema’uma’u crater periodically fluctuated but remained below the inner ledge 75 m below the crater floor. At Pu’u ‘O’o’ crater, lava from sources on the E and S portions of the crater floor fed a lava lake that was formed during 25-26 August. A new source opened at the W edge of the crater floor during 29-30 August, and lava quickly spread N and S along the base of the W crater wall. Volcano Information : Kilauea, one of five coalescing volcanoes that comprise the island of Hawaii, is one of the world’s most active volcanoes. Eruptions at Kilauea originate primarily from the summit caldera or along one of the lengthy E and SW rift zones that extend from the caldera to the sea. About 90% of the surface of Kilauea is formed of lava flows less than about 1,100 years old; 70% of the volcano’s surface is younger than 600 years. A long-term eruption from the East rift zone that began in 1983 has produced lava flows covering more than 100 sq km, destroying nearly 200 houses and adding new coastline to the island.
