Lupi 2018: Pengamatan geofisika dan degassing tanah di gununa lumpur Kalang Anyar

EGU2018-13402 Lupi

Geophysical Research Abstracts Vol. 20, EGU2018-13402, 2018 EGU General Assembly 2018 © Author(s) 2018. 

Pengamatan geofisika dan degassing tanah di gunung lumpur Kalang Anyar, Jawa Timur.

Geophysical and "soil degassing" observations at the Kalang Anyar mud volcano, East Java.

 Matteo Lupi (1), Alessandra Sciarra (2), Adriano Mazzin (3), Aurore Carrier (1), Alwi Husein (4), and Karyono Karyono (5)

(1) University of Geneva, Department of Earth Sciences, Geneva, Switzerland (matteo.lupi@unige.ch), (2) Instituto Nazionale di Geofisica e Vulcanologia, Rome, Italy, (3) Centre for Earth Evolution and Dynamics University of Oslo, (4) Institut Teknologi Sepuluh November, Surabaya, Indonesia, (5) Agency for Meteorology, Climatology and Geophysics, Jakarta, Indonesia

Ditinjau oleh: Dr. Hardi Prasetyo

Science Manager, Misi Nasional Penanggulangan Bencana Lusi,

Kerjasama BPLS-LUSI LAB 2012-2017

LUSI LABORATORIUM ALAM, PUSAT PENELITIAN MUD VOLCANO DI DUNIA

Abstrak

Cekungan busur belakang di Jawa Timur (The East Java back arc basin)  ditandai oleh adanya beberapa sistem semburan lumpur (mud erupting systems), yang posisinya searah di sepanjang diskontinuitas kerak bumi dengan arah timurlaut-baratdaya  (aligned along a major crustal discontinuity striking NE-SW) dan di sepanjang antiklin yang berorentasi Timur-Barat (along a E-W oriented anticline)

Namun yang paling banyak diteliti dari fenomena geologi ini adalah Lusi, suatu induk sedimen sistem hidrotermal (a sediment-hosted hydrothermal system).

Berkembang di pada sistem patahan Watukosek (developed upon the Watukosek fault system), yang memanjang dari busur vulkanik di dekatnya (that extends from the nearby volcanic arc).

Gunung lumpur Kalang Anyar terletak di sepanjang bidang yang sama, 40 km timurlaut dari lokasi Lusi.

Zona kawah gunung lumpur ini ditandai dengan lokasi-lokasi rembesan gas dan lumpur yang tersebar, lebih berlimpah pada bagian tengah.

Penelitian ini menyelidiki gunung lumpur Kalang Anyar dengan mengintegrasikan pendekatan multidisiplin, untuk memantau aktivitasnya dan menjelaskan sinyal gempa yang dihasilkan pada kedalaman (shed light on the seismic signals generated at depth).

Akuisisi profil geolistrik di seluruh struktur (The acquisition of geoelectrical profiles across the structure) digabungkan dengan pengukuran potensial spontan, survei fluks gas, dan pemantauan seismik (was coupled with spontaneous potential measurements, gas flux survey, and seismic monitoring).

Data geoelistrik menunjukkan nilai resistivitas rendah (<1 ohm.m) di daerah sekitar lumpur sampai kedalaman 120 m.

Daerah resistivitas rendah di sekitar semburan mencapai lebar maksimum sekitar 250 m.

Secara keseluruhan, korelasi dari tiga profil geoelistrik menunjukkan hasil yang konsisten, sesuai dengan pengukuran potensial spontan.

Profil fluks gas menunjukkan bahwa daerah di sekitar lokasi rembesan yang difokuskan ditandai oleh paparan gas metana yang lebih intens dan karbon dioksida dalam jumlah yang lebih sedikit,

Demikian pula halnya dengan gunung lumpur lainnya, data gempa menunjukkan sinyal drumbeat pada rentang frekuensi tinggi (yaitu antara 5 Hz dan 30 Hz).

Sinyal hadir di semua stasiun seismik dan sangat dilemahkan pada stasiun yang ditempatkan di bagian tepi bangunan gunung lumpur.

Sinyal seismik semacam itu terlihat pada interval reguler yang bervariasi dari sekitar 40 s sampai 120 detik.

Abstract

The East Java back arc basin is characterized by the presence of several mud erupting systems aligned along a major crustal discontinuity striking NE-SW and along a E-W oriented anticline.

 The most investigated of these geological phenomena is Lusi, a sediment-hosted hydrothermal system developed upon the Watukosek fault system that extends from the nearby volcanic arc.

Kalang Anyar mud volcano is located along the same NE-trending lineament approximately 40 km NE of Lusi.

The crater zone of this mud volcano is characterized by sparsely distributed gas and mud seepage sites that are more abundant in the central part.

This study investigates Kalang Anyar mud volcano combining a multidisciplinary approach to constrain its activity and shed light on the seismic signals generated at depth.

The acquisition of geoelectrical profiles across the structure was coupled with spontaneous potential measurements, gas flux survey, and seismic monitoring.

Geoelectrical data show low resistivity values (< 1 ohm.m) in the regions surrounding the mud vents until 120 m deep.

The region of low resistivity around the vents reaches a maximum width of approximately 250 m.

Overall, the correlation of the three geoelectrical profiles show consistent results, in agreement with spontaneous potential measurements.

 Gas flux profiles indicate that the regions around the focused seepage sites are characterized by more intense soil gas release of methane and, in smaller amounts, carbon dioxide.

Similarly to other mud volcanoes the seismic data show a drumbeat signal in the high-frequency range (i.e. between 5 Hz and 30 Hz).

The signal is present on all the seismic stations and it is strongly attenuated on the stations deployed in the marginal part of the mud volcano edifice.

 Such seismic signal is seen at regular intervals varying from about 40 s to 120 s.