Slip deficit, locking depth and variation of ɸ

Chapter IV Block modeling with GPS measurements

117

near field GPS data along the fault. The differences of blocks rotation component appear clearly in profiles 2 and 3 as vertical steps for each block. Profiles 1 to 4 cross the most blocks of our model (Arabia, Amanous, Iskenderun, and Anatolia) and show that the predicted velocity field and blocks rotation are in good agreement with the observed GPS data.

However this is not the case for the profiles 5 and 6 where a soft difference between observed and calculated velocity field can be easily estimated for the normal and parallel components across the Lebanese restraining bend and part of the northern DSF.

The positive slop in profiles 2 and 3 for the fault perpendicular component of velocity field (black lines) between 120 km and 200 km from the end of profiles indicates significant contraction on the Karasu fault. Profile 1, which is perpendicular to the EAF, shows that the fault is nearly purely left lateral strike-slip with a slip rate of 9.0 mm/yr between the Arabian and Anatolian plates and very small component of along profile velocity (~0.5 mm/y). The same amount of relative velocity between these two blocks can be deduced directly from profiles 2 and 3. The small amount of the fault perpendicular velocity component in the profile 4 and 5 attests for the 1.6 mm/yr of extension along the northern DSF (see figure IV.13 for the values).

In Profile 6, the model does not fit well to the GPS observations. We observe that the GPS data shown in this profile, which are mainly the data of Gomez et al., (2007), can fit better to the kinematic model with a velocity rate of 4.5 mm/yr as proposed by Gomez et al., 2007, while the value predicted from our model is 3.5 mm/yr for the Lebanese restraining bend with a lake of about 1 mm/yr.

Chapter IV Block modeling with GPS measurements

118

slip rate deficit distribution along the fault plan (ɸ*V). For the model D, we use a smooth factor λ = 0.2 and with Z1 fixed at 7 km of depth. This is the depth from surface where ɸ is not allowed to change with depth. In this case we make sure that the inversion will take into account full coupling of fault on the surface which is thought to be the case in the region. The average of formal uncertainties for the values estimates of ɸ in this inversion is 0.2 with 95%

of the uncertainties less than 0.35.

Figure ‎IV.10: Variation of phi (ɸ) parameter along the different faults (DSF, EAF, CF, CA and KOF) from the inversion of model D in Figure IV.5.

Figure IV.10 illustrates that the EAF is fully locked (ɸ = 1) from surface to the depth of ~15 km. The fault creeps only partially down to the depths of 30 km as indicated by the value of ɸ being greater than 0.2. The depth of the coupling along the DSF is relatively shallow and occurs to the depth of ~11 km. Full creep occurs at depths of about 25 km along the northern section of the DSF where as full creep occurs at much deeper depths along the southern section of the DSF. The Karasu fault shows a shallow locking depth of 8 km from surface. The fault is totally creeping after Z2 = 15 km of depth with a very small transition

Chapter IV Block modeling with GPS measurements

119

zone between full locked and full creeping. The Cyprus arc shows the same full locking depth as KF and almost the same way of ɸ value changes which can make the assumption that they are connected and acting as an uniform fault, except that the CA is totally creeping after 20 km with a larger transition zone than KF.

Figure ‎IV.11: Slip rate deficit calculated based on ɸ values and V the relative velocity between the blocks adjacent the faults (DSF, EAF, CF, CA, and KOF). Values of ɸ and V were taken from the inversion of model D in Figure IV.5.

The slip rate deficit, ɸ*V is calculated along the faults from surface to 30 km of depth where V is the slip vector on the faults surface (Figure IV.11). V is varying along the faults due to the rotational component of the relative blocks motions, which results in change of slip deficit over the related faults. On the surface and during the interseismic period, the slip rate deficit represents the lack of slip on the fault surface necessary to satisfy the total relative motion of adjacent blocks. The maximum values of slip rate deficit will be on the surface, and it changes down dip along the transition zone of the fault surface where the faults are partially locked only (0 < ɸ < 1). The value of slip rate deficit can be used to deduce a moment rate on the fault and then expect the magnitude of the next earthquake along this fault in some

Chapter IV Block modeling with GPS measurements

120

conditions (steady build-up of the moment rate over time and one big earthquake to release this moment). A slip deficit of 9.0±0.3 mm/yr is predicted along the EAF from our model (Figure IV.11), 4.5±1.0 mm/yr along the CF, 3.5±0.3 mm/yr along the DSF. The KOF has a slip deficit of 3.5-4.2±0.7 mm/yr. The value is varying along the CA toward NE from 6.0±1.0 mm/yr to 1.2±0.8 mm/yr.