scholarly journals Magma pressure discharge induces very long period seismicity

2021 ◽  
Vol 11 (1) ◽  
Author(s):  
M. Ripepe ◽  
D. Delle Donne ◽  
D. Legrand ◽  
S. Valade ◽  
G. Lacanna
Keyword(s):  
Ground Deformation ◽  
Seismic Source ◽  
Sudden Expansion ◽  
Seismic Signals ◽  
Magma Column ◽  
Long Period ◽  
Magma Dynamics ◽  
Pressure Discharge ◽  
Volcano Seismicity ◽  
Elevation Changes

AbstractVolcano seismicity is one of the key parameters to understand magma dynamics of erupting volcanoes. However, the physical process at the origin of the resulting complex and broadband seismic signals remains unclear. Syn-eruptive very long period (VLP) seismic signals have been explained in terms of the sudden expansion of gas pockets rising in the liquid melt. Their origin is linked to a magma dynamics which triggers the explosive process occurring before the explosive onset. We provide evidence based on acoustic, thermal, and ground deformation data to demonstrate that VLP signals at Stromboli are generated at the top of the magma column mainly after the explosion onset. We show that VLP amplitude and duration scale with the eruptive flux which induces a decompression of 103–104 Pa involving the uppermost ~ 250 m of the feeding conduit. The seismic VLP source represents the final stage of a ~ 200 s long charge and discharge mechanism the magma column has to release excess gas accumulated at the base of a denser and degassed magma mush. The position of the VLP seismic source coincides with the centroid of the shallow mush plug and tracks elevation changes of the magma free surface.

scholarly journals Variation patterns of landslide basal friction revealed from long-period seismic waveform inversion

2019 ◽  
Vol 100 (1) ◽  
pp. 313-327
Author(s):  
Dan Yu ◽  
Xinghui Huang ◽  
Zhengyuan Li
Keyword(s):  
Steady State ◽  
Friction Coefficient ◽  
Water Waves ◽  
Waveform Inversion ◽  
Time History ◽  
Seismic Signals ◽  
Long Period ◽  
Basal Friction ◽  
Seismic Waveform ◽  
Variation Patterns

Abstract A catastrophic landslide struck the Xiaoba village in Fuquan, Guizhou, southwestern China at about 8:30 p.m. (Beijing Time, UTC + 8) on August 27, 2014. The landslide and induced impulse water waves destroyed two villages and killed 23 persons. By reprocessing seismic signals from a seismic network deployed in the surrounding area of the landslide, we recognized the event from low-frequency seismic signals and subsequently performed a long-period seismic waveform inversion to obtain its force–time history. The inversion results reveal that the maximum force for the landslide is 5 × 109 N, and the duration of the landslide is 38.4 s. The landslide reached its maximum velocity of 12.4 m/s at 13.2 s after its initiation, and the mass center plugged into the quarry at 24.2 s. Based on the inversion results, we estimated basal friction of the landslide. We found the friction coefficient rapidly reduces to a relatively steady-state value of ~ 0.4 at a steady-state distance of 35 m and subsequently reduces in a near-linear manner that satisfies the empirical formula $$ \mu = - 1.4d + 0.44 $$μ=-1.4d+0.44, where $$ d $$d is sliding distance in km. The reduction in friction revealed by the formula is compatible with the finding of previous studies for landslides of similar volume in landslide acceleration stage. However, our result does not make it possible for the friction coefficient to increase again in landslide deceleration stage that a velocity-dependent friction law would allow. The friction variation patterns can be used to constrain input parameters in numerical landslide simulation, which can predicate runout distance and deposit areas for massive landslides to carry out landslide hazard assessment.

scholarly journals Teleseismic source parameters and rupture characteristics of the 24 November 1987, Superstition Hills earthquake

1990 ◽  
Vol 80 (1) ◽  
pp. 43-56 ◽  
Author(s):  
Lorraine J. Hwang ◽  
Harold Magistrale ◽  
Hiroo Kanamori
Keyword(s):  
Source Parameters ◽  
Seismic Source ◽  
Point Sources ◽  
Body Waves ◽  
Rupture Velocity ◽  
Total Moment ◽  
Long Period ◽  
The North ◽  
The Difference ◽  
Northern Segment

Abstract Long-period body waves from the 24 November 1987, Superstition Hills earthquake are studied to determine the focal mechanism and spatial extent of the seismic source. The earthquake is a complex event consisting of two spatially distinct subevents with different focal mechanisms. Two consistent models of rupture are developed. For both models, the second subevent begins 8 sec after the initiation of the first subevent and the preferred centroid depth lies between 4 to 8 km. Model 1 consists of two point sources separated by 15 to 20 km along strike of the Superstition Hills fault. Model 2 consists of one point source and one line source with a rupture velocity of 2.5 km/sec with moment release distributed along strike of the focal plane at a distance of 10 to 22 km from the epicenter. These moment release patterns show that a significant amount of long-period energy is radiated from the southern segment of the fault. Total moment release for both models is approximately 8 × 1025 dyne-cm. Both models also suggest a change of dip from near vertical near the epicenter to steeply southwesterly dipping along the southern segment of the fault. The difference in rupture characteristics and fault dips seen teleseismically is also reflected in aftershock and afterslip data, and crustal structure underlying the two fault segments. The northern segment had more aftershocks and a smaller proportion of afterslip than the southern segment. The boundary between the two segments lies at a step in the basement that separates a deeper metasedimentary basement to the south from a shallower crystalline basement to the north.

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