About Swarms of Long - Period Earthquakes at Volcano Nyamuragira of the Virunga Region, Western Rift Valley of Africa (D.R. Congo)

International audienceSwarms of Long Period earthquakes generated by the Nyamuragira volcano for the period from January 2000 to November 2006 before 21 January 2000, 5 February 2001, 25 July 2002, 8 May 2004 and 27 November 2006 Nyamuragira eruptions have been analyzed. Interest is focused on the frequency distribution of these earthquakes and on the variation of the m-value of observed earthquake swarms. It is found that m-values which generally vary between 0.9 and 1.6, and shifts towards larger values of 1.7 to 3.23 two to four months prior to eruptions of the volcano

The monitoring of seismic activity at Nyiragongo volcano through telemetered seismic network Goma Volcano Observatory (Democratic Republic of the Congo)

The eruption, in January 2002, of Mount Nyiragongo in eastern Congo, and the humanitarian disaster that followed in its wake, underlined the critical importance of accurate seismology to predict when such events will take place. Thus, a seismic telemeterd network, with centre in Goma Observatory, was built across Virunga area to help the moniotring of Volcano. Mount Nyiragongo is a volcano in the Virunga Mountains associated with the Great Rift Valley. The most prominent feature of the Democratic Republic of Congo's geology is the Western Rift Zone (WRZ), which runs through its eastern border regions and neighbouring countries (e.g. Uganda, Rwanda, Burundi, Tanzania) between 28°E to 32°E and 4°N to 12°S. The WRZ extends over a 1600 km arc, including lakes Albert, Eduard, Kivu and Tanganyika, until it joins the eastern branch. The Western Rift Valley of Africa has experienced severe earthquakes and volcanic eruptions in recent historical times. Earthquakes with magnitude >=6 are not frequent, but may cause significant destruction. They occur mostly in DRC and neighbouring countries (e.g. Uganda and Tanzania). In 1991, IAVCEI selected the Nyiragongo volcano as the ‘African decade volcano’ for the International Decade of Natural Disaster Reduction (IDNDR) program. Nyiragongo is located about 20 km north of Lake Kivu and 15 km north of Goma, a city of about 500,000 inhabitants. Goma is twinned to Gisenyi in Rwanda, which has a population of about 100,000. Several small villages are also located on the flank of the volcano. Population growth and poor or non-existent planning has led to relatively uncontrolled use of land for building, and the development of sites vulnerable to earthquake and/or volcanic risk.EUROPEAN CENTER FOR GEODYNAMICS AND SEISMOLOGY Royal Museum for Central Africa, B National Museum of Nat. History, LUnpublishedLuxembourg1.4. TTC - Sorveglianza sismologica delle aree vulcaniche attiveope

Preliminary results from seismic monitoring at Nyiragongo Volcano through telemetered seismic network, Goma Volcano Observatory (Gvo, Democratic Republic Of Congo).

Following the catastrophic eruption of Volcano Nyiragongo on January 17, 2002, a great effort has been devoted to the seismic surveillance of volcanoes Nyiragongo and Nyamuragira located at the North of Lake Kivu in the Western branch of the east African rift. The relatively small loss of life in the January 2002 eruption (less than 100 deaths in a population of 500,000) was remarkable, and psychological stress was reportedly the main health consequence in the aftermath of the eruption. In fact, after 2002 january eruption, which was triggered by tectonic spreading of the Kivu rift causing the ground to fracture and allow lava to flow from ground fissures out of the crater lava lake and possibly from a deeper conduit nearer Goma, was installed a telemetered seismic network of 6 permanent stations. Scientists agree that volcano monitoring and contingency planning are essential for forecasting and responding to future trends.OGS TRIESTEUnpublishedROMA1.2. TTC - Sorveglianza geochimica delle aree vulcaniche attiveope

Preliminary results from seismic monitoring at Nyiragongo Volcano (Democratic Republic Of Congo) through telemetered seismic network, Goma Volcano Observatory

Following the January 17, 2002 catastrophic eruption of the Nyiragongo Volcano (Democratic Republic of Congo) located in the western branch of the East African Rift, a great effort has been devoted to the seismic surveillance of this volcanic area. The 2002 eruption destroyed one/tenth of the city of Goma, leaving more than 100,000 homeless. In order to correctly monitor the seismic activity at Nyiragongo volcano for both scientific and civil defence purposes, the Istituto Nazionale di Geofisica e Vulcanologia in cooperation with GVO (Goma Volcanological Observatory), between November 2003 and May 2004 installed a new telemetered seismic network consisting of seven digital stations. The network is operational and seismic signals are continuously recorded at the GVO. In this study, we focus mainly on two aspects: (1) the deployment, in the field, of this new digital seismic network and the related real-time data acquisition system, and (2) the first results from a preliminary data analysis based on 6-month seismic recordings. Based on the waveforms and spectral analysis, long-period and very long period events (both, tectonic and volcanic-tectonic earthquakes), have been detected. Furthermore, we succeeded in locating more than 100 earthquakes. These results should strongly encourage the use of such a network data for seismotectonic studies of the area.Published117-1271.4. TTC - Sorveglianza sismologica delle aree vulcaniche attiveN/A or not JCRreserve

Preliminary results from seismic monitoring at Nyiragongo Volcano through telemetered seismic network, Goma Volcano Observatory (Gvo, Democratic Republic Of Congo).

Following the catastrophic eruption of Volcano Nyiragongo on January 17, 2002, a great effort has been devoted to the seismic surveillance of volcanoes Nyiragongo and Nyamuragira located at the North of Lake Kivu in the Western branch of the east African rift. The relatively small loss of life in the January 2002 eruption (less than 100 deaths in a population of 500,000) was remarkable, and psychological stress was reportedly the main health consequence in the aftermath of the eruption. In fact, after 2002 january eruption, which was triggered by tectonic spreading of the Kivu rift causing the ground to fracture and allow lava to flow from ground fissures out of the crater lava lake and possibly from a deeper conduit nearer Goma, was installed a telemetered seismic network of 6 permanent stations. Scientists agree that volcano monitoring and contingency planning are essential for forecasting and responding to future trends

Stochastic Modeling of the Eruption History of Nyiragongo Volcano in the Virunga Volcanic Province, Western Branch of the East African Rift System

The modeling of statistical distribution of the eruptive frequency provides basic information to quantitatively assess the volcanic hazard and constrain the physics of the eruptive process. Here, we discuss the statistics of the time series of lateral eruptions of the Nyiragongo volcano in the Virunga Volcanic Province, western branch of the East African Rift System. We examine eruption data with a volcanic explosivity index of at least 1 listed in the Global Volcanism Network Bulletins. After investigating the completeness, stationarity, and independence of the eruption time series, we employ five distribution models (Brownian passage time, gamma, log-logistic, lognormal, and Weibull) to fit the repose time. First, we identify a clear tendency for events to cluster in time. We hypothesize two clusters, the ‘pre-1927’ cluster related to the intracraterial and volcanic activity of the lava lake, and the ‘post-1977’ cluster mainly related to lateral eruptions (i.e. those potentially generating lava flows). Using the maximum likelihood estimations, we evaluate the model parameters with a 95% confidence interval. Next, we use the Akaike Information Criterion to determine the most suitable distribution and we perform the Bayesian Model Averaging approach to assess uncertainty issues in model selection process. The results suggest that the BPT distribution provides the best fit for data of lateral eruptions (post-1977). Then we estimate the time-dependent probability of the occurrence of a lateral eruption for the 50-year period between 2022 and 2072. The estimates reach 50.79%, 88.61%, 97.59%, 99.50%, and 99.89% for 2032, 2042, 2052, 2062, and 2072 years, respectively

Stochastic Modeling of the Eruption History of Nyiragongo Volcano in the Virunga Volcanic Province, Western Branch of the East African Rift System

The modeling of statistical distribution of the eruptive frequency provides basic information to quantitatively assess the volcanic hazard and constrain the physics of the eruptive process. Here, we discuss the statistics of the time series of lateral eruptions of the Nyiragongo volcano in the Virunga Volcanic Province, western branch of the East African Rift System. We examine eruption data with a volcanic explosivity index of at least 1 listed in the Global Volcanism Network Bulletins. After investigating the completeness, stationarity, and independence of the eruption time series, we employ five distribution models (Brownian passage time, gamma, log-logistic, lognormal, and Weibull) to fit the repose time. First, we identify a clear tendency for events to cluster in time. We hypothesize two clusters, the ‘pre-1927’ cluster related to the intracraterial and volcanic activity of the lava lake, and the ‘post-1977’ cluster mainly related to lateral eruptions (i.e. those potentially generating lava flows). Using the maximum likelihood estimations, we evaluate the model parameters with a 95% confidence interval. Next, we use the Akaike Information Criterion to determine the most suitable distribution and we perform the Bayesian Model Averaging approach to assess uncertainty issues in model selection process. The results suggest that the BPT distribution provides the best fit for data of lateral eruptions (post-1977). Then we estimate the time-dependent probability of the occurrence of a lateral eruption for the 50-year period between 2022 and 2072. The estimates reach 50.79%, 88.61%, 97.59%, 99.50%, and 99.89% for 2032, 2042, 2052, 2062, and 2072 years, respectively

About swarms of long-period earthquakes at volcano Nyamuragira of the Virunga region, Western Rift Valley of Africa (D.R. Congo)

Swarms of Long Period earthquakes generated by the Nyamuragira volcano for the period from January 2000 to November 2006 before 21 January 2000, 5 February 2001, 25 July 2002, 8 May 2004 and 27 November 2006 Nyamuragira eruptions have been analyzed. Interest is focused on the frequency distribution of these earthquakes and on the variation of the m-value of observed earthquake swarms. It is found that m-values which generally vary between 0.9 and 1.6, and shifts towards larger values of 1.7 to 3.23 two to four months prior to eruptions of the volcano

Preliminary results from seismic monitoring at Nyiragongo Volcano (Democratic Republic Of Congo) through telemetered seismic network, Goma Volcano Observatory

Following the January 17, 2002 catastrophic eruption of the Nyiragongo Volcano (Democratic Republic of Congo) located in the western branch of the East African Rift, a great effort has been devoted to the seismic surveillance of this volcanic area. The 2002 eruption destroyed one/tenth of the city of Goma, leaving more than 100,000 homeless. In order to correctly monitor the seismic activity at Nyiragongo volcano for both scientific and civil defence purposes, the Istituto Nazionale di Geofisica e Vulcanologia in cooperation with GVO (Goma Volcanological Observatory), between November 2003 and May 2004 installed a new telemetered seismic network consisting of seven digital stations. The network is operational and seismic signals are continuously recorded at the GVO. In this study, we focus mainly on two aspects: (1) the deployment, in the field, of this new digital seismic network and the related real-time data acquisition system, and (2) the first results from a preliminary data analysis based on 6-month seismic recordings. Based on the waveforms and spectral analysis, long-period and very long period events (both, tectonic and volcanic-tectonic earthquakes), have been detected. Furthermore, we succeeded in locating more than 100 earthquakes. These results should strongly encourage the use of such a network data for seismotectonic studies of the area