The Experts below are selected from a list of 240 Experts worldwide ranked by ideXlab platform
Linda M Warren - One of the best experts on this subject based on the ideXlab platform.
-
dominant Fault Plane orientations of intermediate depth earthquakes beneath south america
Journal of Geophysical Research, 2014Co-Authors: Linda M WarrenAbstract:The South American subduction zone exhibits considerable variation: the subduction angle alternates between flat and steep; the subducting plate has complex structures; and arc volcanism in the overlying plate has gaps. I investigate the effect of these differences in incoming plate structure and slab geometry on intermediate-depth earthquakes, specifically their Fault orientations and rupture characteristics, and find that slab geometry has the largest impact on Fault orientation. I use rupture directivity to estimate rupture direction and rupture velocity and to distinguish the Fault Plane from the auxiliary Plane of the focal mechanism. From analysis of 163 large (Mw≥5.7) intermediate-depth (60–360 km depth) earthquakes from along the length of South America, estimated rupture azimuths and plunges show no trends, appearing to be randomly distributed on the determined population of Fault Plane orientations, and a majority of earthquakes are made up of multiple subevents. As seen in other subduction zones, subduction segments descending at normal angles have predominantly subhorizontal Faults. Flat slab segments also have a dominant Fault orientation, but those earthquakes slip along the conjugate nodal Plane of the focal mechanism. In strongly curved slab segments, such as at the downdip edge of flat segments where the slab resubducts, earthquakes may slip along either nodal Plane orientation. While both Fault orientations could be consistent with the reactivation of fossil outer rise Faults, the Fault orientations are also consistent with expectations for newly created Faults in agreement with the ambient stress field. Fault reactivation alone does not explain why different Fault orientations are active in segments with different geometries, so the preferred explanation for having regionally consistent Fault orientations is that they minimize the total work of the system. The previously observed predominance of subhorizontal Faults appears to be a consequence of slab geometry.
-
Fault Plane orientations of intermediate‐depth earthquakes in the Middle America Trench
Journal of Geophysical Research, 2008Co-Authors: Linda M Warren, Meredith A Langstaff, Paul G SilverAbstract:[1] Intermediate-depth earthquakes are often attributed to dehydration embrittlement reactivating preexisting weak zones. The orientation of presubduction Faults is particularly well known offshore of Middle America, where seismic reflection profiles show outer rise Faults dipping toward the trench and extending >20 km into the lithosphere. If water is transported along these Faults and incorporated into hydrous minerals, the Faults may be reactivated later when the minerals dehydrate. In this case, the Fault Plane orientations should be the same in the outer rise and at depth, after accounting for the angle of subduction. To test this hypothesis, we analyze the directivity of 54 large (MW ≥ 5.7) earthquakes between 35 and 220 km depth in the Middle America Trench. For 12 of these earthquakes, the directivity vector allows us to identify the Fault Plane of the focal mechanism. Between 35 and 85 km depth, we observe both subhorizontal and subvertical Fault Planes. The subvertical Fault Planes are consistent with the reactivation of outer rise Faults, whereas the subhorizontal Fault Planes suggest the formation of new Faults. Deeper than 85 km, we only observe subhorizontal Faults, indicating that the outer rise Faults are no longer being reactivated. The similarity with previous results from the colder Tonga-Kermadec subduction zone suggests that the mechanism generating these earthquakes, and controlling Fault Plane orientations, depends on pressure rather than temperature or other tectonic parameters and that the observed rupture characteristics constitute a basic feature of intermediate-depth seismicity. Exclusively subhorizontal Faults may result from isobaric rupture propagation or the hindrance of seismic slip on preexisting weak subvertical Planes.
-
Fault Plane orientations of intermediate depth earthquakes in the middle america trench
Journal of Geophysical Research, 2008Co-Authors: Linda M Warren, Meredith A Langstaff, Paul G SilverAbstract:[1] Intermediate-depth earthquakes are often attributed to dehydration embrittlement reactivating preexisting weak zones. The orientation of presubduction Faults is particularly well known offshore of Middle America, where seismic reflection profiles show outer rise Faults dipping toward the trench and extending >20 km into the lithosphere. If water is transported along these Faults and incorporated into hydrous minerals, the Faults may be reactivated later when the minerals dehydrate. In this case, the Fault Plane orientations should be the same in the outer rise and at depth, after accounting for the angle of subduction. To test this hypothesis, we analyze the directivity of 54 large (MW ≥ 5.7) earthquakes between 35 and 220 km depth in the Middle America Trench. For 12 of these earthquakes, the directivity vector allows us to identify the Fault Plane of the focal mechanism. Between 35 and 85 km depth, we observe both subhorizontal and subvertical Fault Planes. The subvertical Fault Planes are consistent with the reactivation of outer rise Faults, whereas the subhorizontal Fault Planes suggest the formation of new Faults. Deeper than 85 km, we only observe subhorizontal Faults, indicating that the outer rise Faults are no longer being reactivated. The similarity with previous results from the colder Tonga-Kermadec subduction zone suggests that the mechanism generating these earthquakes, and controlling Fault Plane orientations, depends on pressure rather than temperature or other tectonic parameters and that the observed rupture characteristics constitute a basic feature of intermediate-depth seismicity. Exclusively subhorizontal Faults may result from isobaric rupture propagation or the hindrance of seismic slip on preexisting weak subvertical Planes.
J Zahradnik - One of the best experts on this subject based on the ideXlab platform.
-
seismic sequence near zakynthos island greece april 2006 identification of the activated Fault Plane
Tectonophysics, 2010Co-Authors: A Serpetsidaki, E Sokos, G A Tselentis, J ZahradnikAbstract:Abstract The April 2006 earthquake sequence near Zakynthos (Western Greece) is analysed to identify the Fault Plane(-s). The sequence (33 events) was relocated to assess physical insight into the hypocenter uncertainty. Moment tensor solution of three major events was performed, simultaneously with the determination of the centroid position. Joint analysis of the hypocenter position, centroid position and nodal Planes indicated sub-horizontal Fault Planes. Moment tensor solutions of 15 smaller events were performed under assumption that the source positions are those of the hypocenters (without seeking centroids). Their focal mechanisms are highly similar and agree with the analysis of the three major events. The preferable seismotectonic interpretation is that the whole sequence activated a single sub-horizontal Fault zone at a depth of about 13 km, corresponding to the interplate subduction boundary. Considering that the Ionian Sea is a high-seismicity area, the identification of the seismic Fault is significant for the seismic hazard investigation of the region.
-
quick Fault Plane identification by a geometrical method application to the mw 6 2 leonidio earthquake 6 january 2008 greece
Seismological Research Letters, 2008Co-Authors: J Zahradnik, F Gallovic, Efthimios Sokos, A Serpetsidaki, A TselentisAbstract:Focal mechanisms of earthquakes provide two nodal Planes. A foolproof method of identifying which one is the Fault Plane is the “seismologist's dream.” This is true because knowledge of causative Faults is of key importance for seismotectonic studies. For example, intermediate-depth earthquakes, such as the one studied in this paper, rarely have known Fault Planes, but the correct interpretation of such a Fault Plane would help constrain regional geodynamic models of subducted plates and stress fields. It is equally important to identify active crustal blind Faults, knowledge of which may improve earthquake hazard assessment. The Fault Plane can sometimes be well “mapped” (constrained) by the spatial distribution of numerous early aftershocks. However, this technique has serious limitations. One of them is the fact that in sparsely instrumented regions, accurate location of weak aftershocks is impossible. Moreover, some events lack numerous aftershocks at the mainshock Fault Plane altogether (this is typical of intermediate-depth earthquakes). The apparently straightforward case, where an earthquake occurs at or close to a geologically well-known Fault, also benefits from an independent check, because the “known” Fault may have a complex tectonic structure at depth. The most challenging task is the quick identification of the earthquake Fault Plane. If made in near real time, it might play a vital role in the fast simulation of strong ground motions (shake maps) for post-event emergency services. If “quick'” means a few hours or a few days after the event, the identification might still greatly contribute to assessing increased spatial probabilities of aftershocks based on the Coulomb stress-loading of neighboring Faults due to the mainshock rupture (McCloskey et al. 2005). Existing methods to identify the Fault Plane from seismograms are based mainly on finite-extent source models: distributed-slip models are generated for both nodal Planes and the one that better fits …
A Cisternas - One of the best experts on this subject based on the ideXlab platform.
-
stress tensor and Fault Plane solutions for a population of earthquakes
Bulletin of the Seismological Society of America, 1990Co-Authors: Luis Rivera, A CisternasAbstract:An algorithm for the simultaneous estimation of the orientation and shape of the stress tensor and the individual Fault Plane solutions for a population of earthquakes is studied. It corresponds to a synthesis of the methods used by Brillinger et al. (1980) to obtain focal mechanisms and by Armijo and Cisternas (1978) for stress tensor analysis in microtectonics. The input data are the polarities of the P arrival and take-off angles for the set of source-station pairs. The method distinguishes, in general, which one of the nodal Planes corresponds to the Fault and gives the direction of the slip. The application to the aftershock sequence of the 1980 Arudy earthquake (Western Pyrenees) shows that the observations may be explained by a single stress tensor producing a N32°E extension, with a likelihood of 95 per cent.
Paul G Silver - One of the best experts on this subject based on the ideXlab platform.
-
Fault Plane orientations of intermediate‐depth earthquakes in the Middle America Trench
Journal of Geophysical Research, 2008Co-Authors: Linda M Warren, Meredith A Langstaff, Paul G SilverAbstract:[1] Intermediate-depth earthquakes are often attributed to dehydration embrittlement reactivating preexisting weak zones. The orientation of presubduction Faults is particularly well known offshore of Middle America, where seismic reflection profiles show outer rise Faults dipping toward the trench and extending >20 km into the lithosphere. If water is transported along these Faults and incorporated into hydrous minerals, the Faults may be reactivated later when the minerals dehydrate. In this case, the Fault Plane orientations should be the same in the outer rise and at depth, after accounting for the angle of subduction. To test this hypothesis, we analyze the directivity of 54 large (MW ≥ 5.7) earthquakes between 35 and 220 km depth in the Middle America Trench. For 12 of these earthquakes, the directivity vector allows us to identify the Fault Plane of the focal mechanism. Between 35 and 85 km depth, we observe both subhorizontal and subvertical Fault Planes. The subvertical Fault Planes are consistent with the reactivation of outer rise Faults, whereas the subhorizontal Fault Planes suggest the formation of new Faults. Deeper than 85 km, we only observe subhorizontal Faults, indicating that the outer rise Faults are no longer being reactivated. The similarity with previous results from the colder Tonga-Kermadec subduction zone suggests that the mechanism generating these earthquakes, and controlling Fault Plane orientations, depends on pressure rather than temperature or other tectonic parameters and that the observed rupture characteristics constitute a basic feature of intermediate-depth seismicity. Exclusively subhorizontal Faults may result from isobaric rupture propagation or the hindrance of seismic slip on preexisting weak subvertical Planes.
-
Fault Plane orientations of intermediate depth earthquakes in the middle america trench
Journal of Geophysical Research, 2008Co-Authors: Linda M Warren, Meredith A Langstaff, Paul G SilverAbstract:[1] Intermediate-depth earthquakes are often attributed to dehydration embrittlement reactivating preexisting weak zones. The orientation of presubduction Faults is particularly well known offshore of Middle America, where seismic reflection profiles show outer rise Faults dipping toward the trench and extending >20 km into the lithosphere. If water is transported along these Faults and incorporated into hydrous minerals, the Faults may be reactivated later when the minerals dehydrate. In this case, the Fault Plane orientations should be the same in the outer rise and at depth, after accounting for the angle of subduction. To test this hypothesis, we analyze the directivity of 54 large (MW ≥ 5.7) earthquakes between 35 and 220 km depth in the Middle America Trench. For 12 of these earthquakes, the directivity vector allows us to identify the Fault Plane of the focal mechanism. Between 35 and 85 km depth, we observe both subhorizontal and subvertical Fault Planes. The subvertical Fault Planes are consistent with the reactivation of outer rise Faults, whereas the subhorizontal Fault Planes suggest the formation of new Faults. Deeper than 85 km, we only observe subhorizontal Faults, indicating that the outer rise Faults are no longer being reactivated. The similarity with previous results from the colder Tonga-Kermadec subduction zone suggests that the mechanism generating these earthquakes, and controlling Fault Plane orientations, depends on pressure rather than temperature or other tectonic parameters and that the observed rupture characteristics constitute a basic feature of intermediate-depth seismicity. Exclusively subhorizontal Faults may result from isobaric rupture propagation or the hindrance of seismic slip on preexisting weak subvertical Planes.
A Serpetsidaki - One of the best experts on this subject based on the ideXlab platform.
-
seismic sequence near zakynthos island greece april 2006 identification of the activated Fault Plane
Tectonophysics, 2010Co-Authors: A Serpetsidaki, E Sokos, G A Tselentis, J ZahradnikAbstract:Abstract The April 2006 earthquake sequence near Zakynthos (Western Greece) is analysed to identify the Fault Plane(-s). The sequence (33 events) was relocated to assess physical insight into the hypocenter uncertainty. Moment tensor solution of three major events was performed, simultaneously with the determination of the centroid position. Joint analysis of the hypocenter position, centroid position and nodal Planes indicated sub-horizontal Fault Planes. Moment tensor solutions of 15 smaller events were performed under assumption that the source positions are those of the hypocenters (without seeking centroids). Their focal mechanisms are highly similar and agree with the analysis of the three major events. The preferable seismotectonic interpretation is that the whole sequence activated a single sub-horizontal Fault zone at a depth of about 13 km, corresponding to the interplate subduction boundary. Considering that the Ionian Sea is a high-seismicity area, the identification of the seismic Fault is significant for the seismic hazard investigation of the region.
-
quick Fault Plane identification by a geometrical method application to the mw 6 2 leonidio earthquake 6 january 2008 greece
Seismological Research Letters, 2008Co-Authors: J Zahradnik, F Gallovic, Efthimios Sokos, A Serpetsidaki, A TselentisAbstract:Focal mechanisms of earthquakes provide two nodal Planes. A foolproof method of identifying which one is the Fault Plane is the “seismologist's dream.” This is true because knowledge of causative Faults is of key importance for seismotectonic studies. For example, intermediate-depth earthquakes, such as the one studied in this paper, rarely have known Fault Planes, but the correct interpretation of such a Fault Plane would help constrain regional geodynamic models of subducted plates and stress fields. It is equally important to identify active crustal blind Faults, knowledge of which may improve earthquake hazard assessment. The Fault Plane can sometimes be well “mapped” (constrained) by the spatial distribution of numerous early aftershocks. However, this technique has serious limitations. One of them is the fact that in sparsely instrumented regions, accurate location of weak aftershocks is impossible. Moreover, some events lack numerous aftershocks at the mainshock Fault Plane altogether (this is typical of intermediate-depth earthquakes). The apparently straightforward case, where an earthquake occurs at or close to a geologically well-known Fault, also benefits from an independent check, because the “known” Fault may have a complex tectonic structure at depth. The most challenging task is the quick identification of the earthquake Fault Plane. If made in near real time, it might play a vital role in the fast simulation of strong ground motions (shake maps) for post-event emergency services. If “quick'” means a few hours or a few days after the event, the identification might still greatly contribute to assessing increased spatial probabilities of aftershocks based on the Coulomb stress-loading of neighboring Faults due to the mainshock rupture (McCloskey et al. 2005). Existing methods to identify the Fault Plane from seismograms are based mainly on finite-extent source models: distributed-slip models are generated for both nodal Planes and the one that better fits …
