TY  - JOUR
A1  - Paschke, Marco
A1  - Stiller, Manfred
A1  - Ryberg, Trond
A1  - Weber, Michael H.
T1  - The shallow P-velocity structure of the southern Dead Sea basin derived from near-vertical incidence reflection seismic data in project DESIRE
JF  - Geophysical journal international
N2  - As a part of the DEad Sea Integrated REsearch (DESIRE) project a near-vertical incidence reflection (NVR) experiment with a profile length of 122 km was completed in spring 2006. The profile crossed the southern Dead Sea basin (DSB), a pull-apart basin due to the strike-slip motion along the Dead Sea Transform (DST). The DST with a total displacement of 107 km since about 18 Ma is part of a left-lateral fault system which connects the spreading centre in the Red Sea with the Taurus collision zone in Turkey over a distance of about 1100 km. The seismic experiment comprises 972 source locations and 1045 receiver locations. Each source was recorded by similar to 180 active receivers and a field data set with 175 000 traces was created. From this data set, 124 444 P-wave first-break traveltimes have been picked. With these traveltimes a tomographic inversion was carried out, resulting in a 2-D P-wave velocity model with a rms error of 20.9 ms. This model is dominated by a low-velocity region associated with the DSB. Within the DSB, the model shows clearly the position of the Lisan salt diapir, identified by a high-velocity zone. A further feature is an unexpected laterally low-velocity zone with P-velocities of 3 km s1 embedded in regions with 4 km s1 in the shallow part on the west side of the DSB. Another observation is an anticlinal structure west of the DSB interpretated to the related Syrian arc fold belt.
KW  - Tomography
KW  - Controlled source seismology
KW  - Transform faults
Y1  - 2012
U6  - https://doi.org/10.1111/j.1365-246X.2011.05270.x
SN  - 0956-540X
VL  - 188
IS  - 2
SP  - 524
EP  - 534
PB  - Wiley-Blackwell
CY  - Malden
ER  - 
TY  - JOUR
A1  - Dahm, Torsten
A1  - Fischer, Tomas
T1  - Velocity ratio variations in the source region of earthquake swarms in NW Bohemia obtained from arrival time double-differences
JF  - Geophysical journal international
N2  - Crustal earthquake swarms are an expression of intensive cracking and rock damaging over periods of days, weeks or month in a small source region in the crust. They are caused by longer lasting stress changes in the source region. Often, the localized stressing of the crust is associated with fluid or gas migration, possibly in combination with pre-existing zones of weaknesses. However, verifying and quantifying localized fluid movement at depth remains difficult since the area affected is small and geophysical prospecting methods often cannot reach the required resolution.
 We apply a simple and robust method to estimate the velocity ratio between compressional (P) and shear (S) waves (upsilon(P)/upsilon(S)-ratio) in the source region of an earthquake swarm. The upsilon(P)/upsilon(S)-ratio may be unusual small if the swarm is related to gas in a porous or fractured rock. The method uses arrival time difference between P and S waves observed at surface seismic stations, and the associated double differences between pairs of earthquakes. An advantage is that earthquake locations are not required and the method seems lesser dependent on unknown velocity variations in the crust outside the source region. It is, thus, suited for monitoring purposes.
 Applications comprise three natural, mid-crustal (8-10 km) earthquake swarms between 1997 and 2008 from the NW-Bohemia swarm region. We resolve a strong temporal decrease of upsilon(P)/upsilon(S) before and during the main activity of the swarm, and a recovery of upsilon(P)/upsilon(S) to background levels at the end of the swarms. The anomalies are interpreted in terms of the Biot-Gassman equations, assuming the presence of oversaturated fluids degassing during the beginning phase of the swarm activity.
KW  - Tomography
KW  - Earthquake source observations
KW  - Volcano seismology
Y1  - 2014
U6  - https://doi.org/10.1093/gji/ggt410
SN  - 0956-540X
SN  - 1365-246X
VL  - 196
IS  - 2
SP  - 957
EP  - 970
PB  - Oxford Univ. Press
CY  - Oxford
ER  -