Principal Horizontal Stress Orientations Research Articles

Modelling principal stress orientations in the Arabian Plate using plate velocities

Abstract We model maximum principal horizontal stress orientations in the Arabian Plate using a 3D finite element approach in conjunction with plate velocities. To capture the impact of geometry and tectonics, the model considers an accurate plate boundary shape and associated deformations. Three primary geological units represent plate architecture: sedimentary cover, crust and upper mantle. The mesh resolution varies to capture important geometrical features. Subsequently, we calculate the stress field using the force balance equation. Displacement boundary conditions are evaluated as accumulative deformation. NE–SW maximum principal horizontal stress (S Hmax ) azimuths dominate in northeastern Saudi Arabia and Kuwait, whilst NW–SE to NNW–SSE define the Dead Sea area. The Red Sea Basin and Saudi Arabia's interior is characterized by north–south S Hmax azimuths. Iraq's western area shows azimuths from NNW–SSE to NW–SE due to the collision at the Zagros Mountain Range, but changes to NE–SW in the east at the Zagros fold-and-thrust belt. An extensive literature review reveals publicly available S Hmax azimuth data which augment the sparse records compiled in the World Stress Map database. Our simulated S Hmax azimuths are consistent with these data. The results further corroborate ongoing tectonic processes, deepen our understanding of in situ stress variation drivers and inform current elastic deformation mechanisms in the Arabian Plate.

Magma storage in a strike-slip caldera.

Silicic calderas form during explosive volcanic eruptions when magma withdrawal triggers collapse along bounding faults. The nature of specific interactions between magmatism and tectonism in caldera-forming systems is, however, unclear. Regional stress patterns may control the location and geometry of magma reservoirs, which in turn may control the spatial and temporal development of faults. Here we provide new insight into strike-slip volcano-tectonic relations by analysing Bouguer gravity data from Ilopango caldera, El Salvador, which has a long history of catastrophic explosive eruptions. The observed low gravity beneath the caldera is aligned along the principal horizontal stress orientations of the El Salvador Fault Zone. Data inversion shows that the causative low-density structure extends to ca. 6 km depth, which we interpret as a shallow plumbing system comprising a fractured hydrothermal reservoir overlying a magmatic reservoir with vol% exsolved vapour. Fault-controlled localization of magma constrains potential vent locations for future eruptions.

Pliocene shortening direction in Nankai Trough off Kumano, southwest Japan, Sites IODP C0001 and C0002, Expedition 315: Anisotropy of magnetic susceptibility analysis for paleostress

Integrated Ocean Drilling Program Expedition 315 recovered cores from accretionary units, which are overlain by cover sequences, at a site on the hanging wall of the mega‐splay fault (C0001), and at a seaward margin of a forearc basin (C0002) in Nankai Trough off Kumano, Japan. In order to investigate the amount and the style of deformation and shortening direction of the accretionary prism units, anisotropy of magnetic susceptibility (AMS) of cored samples were measured. AMS of the late Pliocene to late Miocene accretionary prism at C0001 reveals a deformed magnetic ellipsoid (prolate type), and a restored direction of the AMS orientation indicates northwest–southeast shortening which is the same as the present‐day stress field measured by borehole breakout. The older Miocene accretionary prism cored beneath the forearc basin at C0002 does not show a typical prolate type but more oblate feature in parallel to plunged bedding planes. This type can be interpreted as an intermediate type between prolate and oblate types, by indicatives of AMS parameters, which was formed under a bedding vertical loading and a relatively weakly lateral compaction. The restored AMS orientation of the accretionary prism beneath the forearc basin also indicates the northwest‐southeast shortening which is different from the present‐day principal horizontal stress orientations at C0002. It is supposed that the shortening direction had been recorded in Pliocene time probably when the sequence was sited in the outer wedge. The northwest–southeast directions of AMS in the Pliocene time agree with the past subducting direction of the Philippine Sea Plate since the Pliocene.

Correction to “Principal horizontal stress orientations prior to the 2011 Mw9.0 Tohoku-Oki, Japan, earthquake in its source area”

Correction to “Principal horizontal stress orientations prior to the 2011 M_w9.0 Tohoku-Oki, Japan, earthquake in its source area”

Principal horizontal stress orientations prior to the 2011 Mw9.0 Tohoku-Oki, Japan, earthquake in its source area

[1] We determined principal horizontal stress orientations as of 1999 at sites in the source area of the 2011 Mw 9.0 Tohoku-Oki earthquake, on the deep-sea terrace of the Japan Trench. The maximum principal horizontal stress orientation at site 1151 of Ocean Drilling Program Leg 186, located in an aseismic zone, was east-southeast, parallel with the plate convergence direction; and the stress orientation at site 1150 of Leg 186, in a seismically active zone, was south-southeast, suggestive of a local stress feature due to the influence of seismic activity. Aftershocks with normal faulting mechanisms, observed in the hanging wall of the plate interface that ruptured during the Tohoku-Oki earthquake, indicate a normal faulting postseismic stress regime, which clearly differs from the stress state prior to the earthquake. Consequently, the stress state may have changed from a reverse to a normal faulting stress regime during the Tohoku-Oki earthquake sequence.

Present‐day principal horizontal stress orientations in the Kumano forearc basin of the southwest Japan subduction zone determined from IODP NanTroSEIZE drilling Site C0009

A 1.6 km riser borehole was drilled at site C0009 of the NanTroSEIZE, in the center of the Kumano forearc basin, as a landward extension of previous drilling in the southwest Japan Nankai subduction zone. We determined principal horizontal stress orientations from analyses of borehole breakouts and drilling‐induced tensile fractures by using wireline logging formation microresistivity images and caliper data. The maximum horizontal stress orientation at C0009 is approximately parallel to the convergence vector between the Philippine Sea plate and Japan, showing a slight difference with the stress orientation which is perpendicular to the plate boundary at previous NanTroSEIZE sites C0001, C0004 and C0006 but orthogonal to the stress orientation at site C0002, which is also in the Kumano forearc basin. These data show that horizontal stress orientations are not uniform in the forearc basin within the surveyed depth range and suggest that oblique plate motion is being partitioned into strike‐slip and thrusting. In addition, the stress orientations at site C0009 rotate clockwise from basin sediments into the underlying accretionary prism.

Geodetic constraints on areal changes in the Pacific–North America plate boundary zone: What controls Basin and Range extension?

Using ∼1500 geodetic velocities we model the present-day spatial patterns of areal changes inside the Pacific–North America plate boundary zone. From this model we show that between the central Gulf of California and the Queen Charlotte Islands there is no significant net change in surface area. This zero net areal-change result allows us to relate regions of areal growth to areas of equivalent contraction elsewhere within the plate boundary zone. We find that areal growth of the Basin and Range province (BRP) and its eastern margin (∼5.2 ± 0.1 × 10 3 m 2 /yr) is balanced by areal reduction near northwestern California between 38°N and 42°N. The San Andreas fault system south of 38°N and the plate boundary zone north of ∼42°N (including the Juan de Fuca and Gorda Ridge systems) each have no significant net areal change. Our results suggest a kinematic relationship between extension in the BRP and contraction near the northern California Coast Ranges and Klamath Mountains. From these observations we propose that, although BRP extension may be caused by internal forces, the southernmost Cascadia subduction zone provides a “window of escape” that acts as a stress guide to BRP extension as well as northwestward Sierra Nevada motion. Such a dynamic model is consistent with independent findings that (1) the least principal horizontal stress orientations in the BRP are toward northern California, (2) extension directions in the BRP have changed orientation to track the northward migration of the Mendocino triple junction, and (3) the southernmost Cascadia subduction zone is a relatively weak plate boundary.

Moment tensor solutions for small and moderate earthquakes in the Ibero‐Maghreb region

We applied time domain moment tensor inversion of local and regional waveforms to small and moderate (Mw = 3.5–5.7) shallow earthquakes from the Iberian Peninsula, northern Morocco, and northern Algeria. For the 6+ years period from November 1995 to March 2002 and the previous Network of Autonomously Recording Seismograms (NARS) experiment, moment tensor solutions were obtained for 58 events, considerably increasing the total number of available solutions in the study area. For each event we performed a moment tensor inversion and a double‐couple grid search. For simple faulting events the grid search is valuable as a quality test for its ability to reveal potential ambiguities of the solutions and to assess confidence limits of fault plane parameters or principal axes orientation. The computed mechanisms show regional consistency: A large part of the Iberian Peninsula is characterized by normal faulting mechanisms with SW‐NE oriented T axes. Thrusting and SE‐NW compression is dominant in Algeria. In the Alboran Sea, the westernmost part of the Mediterranean, and the transition between both regimes, strike‐slip mechanisms dominate with approximately N‐S oriented P axes. This pattern suggests a regional anomaly characterized by clockwise rotation of the principal horizontal stress orientations.

Stress orientations found in north‐east Germany differ from the West European trend

Knowledge about the acting stresses is of crucial importance for understanding the tectonics of a region. Data about the stress field in north‐eastern Germany used to be very rare. In general, it was assumed that the orientation of the larger horizontal principal stress (SH) is similar to that found for western Germany and central West‐Europe, i.e. NW–SE. To check this, several borehole logs of the late 1980s were analysed for information on the principal horizontal stress orientations: they include Four‐Arm‐Dipmeter and borehole televiewer data from 15 boreholes. The depth range of our stress results reaches from 1500 to 6700 m. They were compared to a few other data, especially from hydraulic fracturing, and to recent findings on the stresses in the Northwest German basin. In contrast to expectation, SH derived from breakout orientations below the salt layers displayed N to NE orientation. The latter was found at 10 locations spread over the NE‐German basin from Berlin to the Baltic sea, from the Polish border to the former border between East and West Germany. Moreover, this stress rotation in the subsaline formations seems to be the continuation of a trend found in the NW German basin.