Search for: All records

High-resolution seismic images are essential to gain insights into tectonic and geodynamical processes and assess seismic hazards. We constructed a P-wave model, MEPT (Middle East P-wave Travel-time), of the upper mantle beneath the Middle East and the surrounding region, which has a complex tectonic and geological history embodying various plate boundaries such as spreading ridges, subduction, suture zones, and strike-slip faults causing destructive earthquakes, specifically in Iran, Caucasus and Anatolia, and active volcanism. We use data from the ISC-EHB bulletin and onset-time readings of first-arrival P waves from waveforms recorded in the Arabian Peninsula. The additional onset-time readings from the regional waveform data significantly improve the resolution of the structure underneath the Arabian Peninsula, clearly indicating the boundary between the Arabian platform and the Arabian shield down to about 300 km depth, highlighted by slow and fast wavespeed perturbations in the upper mantle. Consistent with previous studies, we observe the Arabian-Eurasian collision, the Red Sea rifting, the Hellenic Arc, and low-velocity anomalies beneath the lithosphere of the Red Sea and the west of the Arabian shield. Our model supports the connection of the slow wavespeed anomalies in the lithosphere along the Red Sea to the Afar plume and shows evidence for smaller mantle upwellings underneath the Arabian plate and Jordan. 

Abstract Floating seismographs (Mobile Earthquake Recorder in Marine Areas by Independent Divers project “MERMAIDs”) record the data at depth at a location that is determined by linearly interpolating between the Global Positioning System positions when surfacing, assuming a constant drift velocity at depth. We study the influence of a changing drift velocity between surfacings and of a curvature of the drift trajectory. We separate localizations that directly follow a triggered ascent from those that are interpolated later. The first ones have on average a mislocation of 99 m due to curvature of the drift, against 685 m for interpolated localizations. Mislocations due to nonconstant velocity are somewhat smaller. Equivalent time errors have a distribution with heavier tails than Gaussian. The halfwidth of the 95% interval for equivalent arrival-time errors is smaller than 27 ms if the seismogram recording triggers an immediate ascent. If the recording is transmitted at a later surfacing, the interpolation is less precise with a 95% confidence interval halfwidth of 222 ms, but 67% of the errors are below 44 ms. We conclude that the localization errors have no significant impact on the accuracy of picked arrival times. 

ABSTRACT We describe an algorithm to pick event onsets in noisy records, characterize their error distributions, and derive confidence intervals on their timing. Our method is based on an Akaike information criterion that identifies the partition of a time series into a noise and a signal segment that maximizes the signal-to-noise ratio. The distinctive feature of our approach lies in the timing uncertainty analysis, and in its application in the time domain and in the wavelet timescale domain. Our novel data are records collected by freely floating Mobile Earthquake Recording in Marine Areas by Independent Divers (MERMAID) instruments, midcolumn hydrophones that report triggered segments of ocean-acoustic time series.