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We determine the finite-fault slip distribution of the 2001 Kunlun earthquake ( Ms= 8.1) by inverting teleseismic waveforms, as constrained by geological and remote sensing field observations. The spatial slip distribution along the 400-km-long fault was divided into five segments in accordance with geological observations. Forward modelling of regional surface waves was performed to estimate the variation of the speed of rupture propagation during faulting. For our modelling, the regional 1-D velocity structure was carefully constructed for each of six regional seismic stations using three events with magnitudes of 5.1–5.4 distributed along the ruptured portion of the Kunlun fault. Our result shows that the average rupture velocity is about 3.6 km s−1, consistent with teleseismic long period wave modelling. The initial rupture was almost purely strike-slip with a rupture velocity of 1.9 km s−1, increasing to 3.5 km s−1 in the second fault segment, and reaching a rupture velocity of about 6 km s−1 in the third segment and the fourth segment, where the maximum surface offset, with a broad fault zone, was observed. The rupture velocity decelerated to a value of 3.3 km s−1 in the fifth and final segment. Coseismic slip on the fault was concentrated between the surface and a depth of about 10 km. We infer that significant variations in rupture velocity and the observed fault segmentation are indicative of variations in strength along the interface of the Kunlun fault, as well as variations in fault geometry. [ABSTRACT FROM AUTHOR]

High-frequency seismic waves (> 1Hz) contain valuable information indicating the existence of random heterogeneity in the lithosphere. These waves, namely Po and So coda, are typically characterized by their dominance over long distance range (up to 3000 km), high-frequency content and low amplitude decay. Their generation in the oceanic lithosphere is thought to be a result of multiple scattering of P and S waves linked to small-scale heterogeneities within the plate.Previous efforts focused on plates of moderate (15-60 Ma) to old age (> 100 Ma) but no observation and modelling has been done aiming at very young plates (e.g., < 10 Ma).In order to contribute to new insights on the nature of these waves in very young oceanic plates, we analysed P and S-coda waves recorded by Ocean Bottom Seismometers (OBSs) of Cascadia Initiative deployed in Juan de Fuca and Gorda plate. This effort will provide new constrain on the presence or absence of small-scale heterogeneities in a very young plate (< 10 Ma). We analyse apparent P wave velocity, radiation patterns of P wave, and amplitude decay of P and S-coda waves in three component seismogram envelopes over the frequency band of 1 to 16 Hz. The observations not only show changes in the P wave apparent velocity varying between 7.3 to 8.2 km/s, but also reveal considerable spatial variation in the amplitude decay of the P and S-coda. To obtain direct evidence of the azimuthal variation of the amplitude distribution, we analyse a series of envelopes in vertical component over a limited range of azimuth. The apparent radiation pattern obtained for P waves, shows important distortion of the pattern. Together, these results, suggest a distortion and a change in the velocity as frequency increases and they could potentially be explained by the presence of small-scale heterogeneities. [ABSTRACT FROM AUTHOR]

Long period volcanic tremors (LPTs), typically termed as VLP, have been widely observed in many volcanic systems around the world. LPTs in different volcanic settings are often repetitive, suggesting a nondestructive source and providing critical insights into the fluid dynamic processes operating inside a volcanic system. The diversities of LPTs in a single volcanic system, however, are not necessarily well understood and they could potentially help monitor the state of shallow volcanic conduit and its link to upcoming eruptions. In the southwest Japan, LPTs are repetitive beneath Aso volcano and previous efforts have characterised LPTs of ~15 second period and a duration of several tens of seconds. These LPTs are regarded as a result of resonance of fluid-filled crack-like conduit located near the hydrothermal reservoir at the sea level. To explore diverse LPTs (DLPTs) at Aso volcano, we carry out systematic analysis of continuous data at V-net and JMA volcanic seismic network between 2011 and 2016, during which Aso volcano became very active with frequent phreatic eruptions, intermittent Strombolian eruptions (2014) as well as two phreatomagmatic eruptions in September 2015 and October 2016. A two-step process is applied to the detection of DLPT and construction of the catalog. The first stage involves continuous wavelet transformation to search for LPTs with spectra features comparable to that of the template. We identify 3 families of LPTs with virtually the same polarisation, but different waveform shapes, resonance period, or/and polarities. These LPT families are subsequently used in the second stage to conduct an exhausted search through a matched filter algorithm.We will present the DLPTs catalog and summarise the similarity and difference among DLPTs. Most importantly, we find different LPT families are not mutually exclusive in time, but each LPT family does exert dominance over the pre-eruptive, syn-eruptive or inter-eruptive stage, respectively. While the resonance period and quality factor Q of each LPT family do vary over time, these temporal patterns are highly correlated among different LPT families. In the context of fluid-filled crack-like conduit, this observation may allow us to monitor changes in triggering source properties (e.g., location, spatial extent), conduit geometry and fluid properties inside the shallow volcanic conduit. [ABSTRACT FROM AUTHOR]

In the southwest Japan, long-period tremors (LPTs) in Aso volcano have been observed since the pioneering work by Sassa (1935). Similar to VLPs discovered in other volcanoes, LPTs typically have a resonance period of ~15 seconds and they are repetitive and time-invariant in their location and mechanism. It is considered that LPTs represent the resonance of a crack-like volcanic conduit located close to the active first crater, with a source depth near the sea level. While surface degassing/eruption and magmatic heating (or hot gas) are often invoked to trigger LPTs, seismic observation indicative of direct triggering remain elusive. We previously constructed LPT catalog between 2011 and 2016 and identified diverse LPT families. After removing the background trend, we align and stack broadband displacement and horizontal tilt borehole recordings with respect to the arrival of LPTs. LPT stacked waveforms are accompanied by a very weak (e.g,. vertical displacement of ~ 1 μm and horizontal tilt of < 1 nrad) static offset with a rise time of 50-100 seconds. To obtain robust estimate of waveform polarisation over time, waveform data in the passed band of 100-200 sec period are used as a proxy of static offset. Interestingly, these waveform polarisations show no appreciable change over the 6-year period, but they are distinct from those of LPTs, suggesting another repetitive, but non-destructive source located away from the LPT source. Moment tensor inversion locates a deep source at about 3.2 km depth, just between the LPT source and the inferred magma chamber at ~ 5-6 km depth. The source mechanism of the deep source is best represented by the combination of an isotropic source and a vertical crack orienting approximately east-west. These observations not only provide causal evidence of direct and repetitive triggering of LPT from a deep triggering source, such a triggering source potentially serves as a buffer between the LPT source and the magma chamber beneath a well developed caldera. We will discuss the triggering threshold of LPT, possible triggering mechanism and the role of the deep triggering source in intra-crustal magma transport over the 2011-2016 eruption cycle. [ABSTRACT FROM AUTHOR]