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Abstract. The characterisation of seismic sources with timereversed wave fields is developing into a standard technique that has already been successful in numerous applications. While the time-reversal imaging of effective point sources is now well-understood, little work has been done to extend this technique to the study of finite rupture processes. This is despite the pronounced non-uniqueness in classic finite source inversions.The need to better constrain the details of finite rupture processes motivates the series of synthetic and real-data time reversal experiments described in this paper. We address questions concerning the quality of focussing in the source area, the localisation of the fault plane, the estimation of the slip distribution and the source complexity up to which timereversal imaging can be applied successfully. The frequency band for the synthetic experiments is chosen such that it is comparable to the band usually employed for finite source inversion.Contrary to our expectations, we find that time-reversal imaging is useful only for effective point sources, where it yields good estimates of both the source location and the origin time. In the case of finite sources, however, the timereversed field does not provide meaningful characterisations of the fault location and the rupture process. This result cannot be improved sufficiently with the help of different imaging fields, realistic modifications of the receiver geometry or weights applied to the time-reversed sources.The reasons for this failure are manifold. They include the choice of the frequency band, the incomplete recording of wave field information at the surface, the excitation of largeCorrespondence to: S. Kremers (kremers@geophysik.uni-muenchen.de) amplitude surface waves that deteriorate the depth resolution, the absence of a sink that should absorb energy radiated during the later stages of the rupture process, the invisibility of small slip and the neglect of prior information concerning the fault geometry and the inherent smoothness of seismologically inferred Earth models that prevents the beneficial occurrence of strong multiple-scattering.The condensed conclusion of our study is that the limitations of time-reversal imaging -at least in the frequency band considered here -start where the seismic source stops being effectively point-localised.

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Mt. Yasur volcano (Vanuatu) has been increasingly recognized for its high‐frequency Strombolian eruptions. Strombolian activity is often regarded as a product of the rapid ascent of gas slugs originating from a deep magma, which mingle with a batch of shallow magma upon eruption. Heterogeneous crystal distribution as well as bimodal bubble‐size distributions, in the eruptive products, generally supports this view. Here, the Strombolian activity at Mt. Yasur is analyzed. A rheological investigation indicates that the basaltic‐andesitic eruptive products contain an apparently homogeneous glass phase and yet, exhibit evidence of a distinct range of glass transition temperatures with multiple peaks occurring in individual samples. Such anomalous behavior is proposed to result from the mingling of magmas with contrasting oxidation states. The unstable nature of the measured glass transition behavior leads us to the inference that mingling is located in the shallow parts of the eruptive conduits, partly driven by rejuvenation of material slumped from the crater walls into an open conduit system. The dynamics of this process may expose the periodicity of the eruptions themselves.