Though the idea of pre-impact recovery preparedness planning has recently been promoted by federal and state governments, very little research has been done to evaluate how it affects the process of disaster recovery. This research attempts to understand how pre-impact recovery planning affects housing reconstruction by examining the relationship of pre-impact recovery planning with housing reconstruction speed and the use of mitigation techniques during housing reconstruction. This study was conducted by comparing two cases, the City of Los Angeles, California and Taichung County in Taiwan. This study finds that having a pre-impact preparedness recovery plan increases the speed of housing reconstruction. The relationship between having a pre-impact recovery preparedness plan and the extent to which hazard mitigation is integrated into the recovery process is not very clear, but the experience of the City of Los Angeles suggests that having a pre-impact recovery plan allows local officials to make more effective use of the “window of opportunity” after disaster.

The lower Da-An River in western Taiwan was uplifted ~10 during the 1999 Mw 7.6 Chi-Chi earthquake, resulting in a 20- to 30-m-deep bedrock gorge. However, the amount of coseismic displacement along the channel bed does not fully explain the resulting bedrock channel incision. Using a series of aerial photographs, digital terrain models (DEM), and real-time kinematic global positioning system (RTK GPS) surveys, we characterized knickpoint retreat and fluvial incision in the Da-An River gorge. We also analyzed discharge and precipitation data and collected measurements of rock strength and joint plane orientations to understand the climatic, lithological, and structural influence on the evolution of the actively incising gorge. Two stages of fluvial incision and knickpoint migration are identified in the gorge following surface uplift during the Chi-Chi earthquake. From 1999 to 2004, 3 to 5 m of alluvium was removed from the channel bed, followed by 3 to 4 m of bedrock channel incision. The knickpoint generated immediately after the earthquake stayed where the uplift occurred at this time. Since 2005, the channel bed has lowered rapidly with local incision rate as high as 15 m/yr in terms of knickpoint migration. The average knickpoint migration rate over the period 2005 to 2009 was 238 m/yr; total upstream migration from the location of knickpoint formation was 1190 m. While tectonic uplift formed the knickpoint and set the stage for channel incision, climate played a critical role in accelerating the fluvial response to coseismic displacement. More than 20 m of bedrock channel incision and 1180 m knickpoint migration occurred during the post-2004 typhoon seasons (May-October). Based on repeat surveys of the Da-An River longitudinal profile and analysis of precipitation and discharge data, we suggest that a discharge threshold of 1200 to 2600 m³/s is required to initiate upstream knickpoint migration. However, once the threshold is exceeded, bedding dip becomes the primary control on rates and patterns of knickpoint propagation. Rotation occurred in a hinge zone where the bedding dips change from horizontal to upstream-dipping, while replacement was observed in the strata dipping upstream. The highest knickpoint migration rates (> 300 m/yr) were recorded in flat-lying, horizontal strata (< 10º) where parallel retreat was the dominate process. Overall, the knickpoint propagation followed the process of replacement behavior, in which the height of knickpoint decreases while migrating upstream. Thus, while tectonic processes set the initial conditions for knickpoint propagation in the Da-An River, the response time of the fluvial system to this forcing is strongly dependent on climate and local structure.

Temporal changes of seismic velocity and anisotropy in the shallow crust are quantified using local earthquakes recorded at a 200-m-deep borehole station CHY in Taiwan. This station is located directly above the hypocenter of the 10/22/1999, M6.4 Chia-Yi earthquake. Three-component seismograms recorded at this station show clear direct (up-going) and surface-reflected (down-going) P- and S-waves, and S-wave splitting signals. The two-way travel times in the top 200 m is obtained by measuring the time delays between the up-going and down-going waves in the auto-correlation function. The S-wave travel times measured in two horizontal components increase by ~1-2% at the time of Chia-Yi main shock, and followed by a logarithmic recovery, while the temporal changes of S-wave splitting and P-wave are less than 1% and are not statistically significant. We obtain similar results by grouping earthquakes into clusters according to their locations and waveform similarities. This suggests that the observed temporal changes are not very sensitive to the seismic ray path below CHY, but are mostly controlled by the variation of material property in the top 200 m of the crust. We propose that strong ground motions of the Chia-Yi main shock cause transient openings of fluid-filled microcracks and increases the porosity in the near-surface layers, followed by a relatively long healing process. Because we observe no clear changes in the shear wave anisotropy, we infer that the co-seismic damages do not have a preferred orientation. Our results also show a gradual increase of time delays for both the fast and slow S-waves in the previous 7 years before the Chia-Yi main shock. Such changes might be caused by variations of water table, sediment packing or other surficial processes.

Η ΒΥΠ διαθέτει αντίτυπο της διατριβής σε έντυπη μορφή στο βιβλιοστάσιο διδακτορικών διατριβών που βρίσκεται στο ισόγειο του κτιρίου της. / Εκτελώντας δυναμικές αναλύσεις με χρήση πεπερασμένων στοιχείων, αναλύεται η σεισμική απόκριση τεσσάρων τοίχων αντιστήριξης οπλισμένου εδάφους στην Ταϊβάν με στοιχεία πρόσοψης κυβόλιθους. Οι τοίχοι, των οποίων τα ύψη κυμαίνονται από 3.20 m έως 5.60 m και έχουν ως οπλισμούς στρώσεις γεωπλέγματος, υποβλήθηκαν στο σεισμό Chi-Chi (1999) και η συμπεριφορά τους κρίθηκε από επιτυχής έως ανεπιτυχής: δύο από αυτούς κατέρρευσαν, ένας υπέστη μόνο ελαφρές βλάβες, ενώ ο τέταρτος τοίχος παρέμεινε πρακτικά ανέπαφος. Η μη-γραμμική ανάλυση βασίσθηκε στα γνωστά γεωμετρικά και μηχανικά χαρακτηριστικά του κάθε τοίχου, του γεωπλέγματος, των γεωτεχνικών συνθηκών σε κάθε θέση, του είδους και των ιδιοτήτων του υλικού επίχωσης. Η συμπεριφορά του εδαφικού υλικού προσομοιώθηκε κάνοντας χρήση του κριτηρίου Mohr-Coulomb, ενώ ως διέγερση βάσης στις δυναμικές αναλύσεις πεπερασμένων στοιχείων χρησιμοποιήθηκαν τα καταγεγραμμένα επιταχυνσιογραφήματα κοντά στις θέσεις των τοίχων. Τα αποτελέσματα των αναλύσεων (και ειδικά η εκτιμώμενη παραμορφωμένη μορφή των τοίχων) επαλήθευσαν την παρατηρούμενη συμπεριφορά των τοίχων. Βασιζόμενοι στα αποτελέσματα, βρέθηκαν οι λόγοι της ανεπιτυχούς συμπεριφοράς των δύο τοίχων που κατέρρευσαν, ενώ εξηγήθηκε η διαφοροποίηση της συμπεριφοράς των δύο τοίχων που δεν υπέστησαν βλάβες. Επιπροσθέτως, πραγματοποιήθηκαν παραμετρικές αναλύσεις για να ευρεθεί η επίδραση σημαντικών παραμέτρων σχεδιασμού, όπως το βάθος θεμελίωσης του τοίχου, η απόσταση και το μήκος των οπλισμών, η συνεισφορά των ράβδων σύνδεσης στην ευστάθεια των στοιχείων πρόσοψης και η συνεισφορά της ανώτατης στρώσης οπλισμού στην ευστάθεια του τοίχου. Επίσης αναλύθηκε η ευστάθεια των τοίχων χρησιμοποιώντας ένα εμπορικά διαθέσιμο λογισμικό οριακής ισορροπίας, το οποίο βρέθηκε ικανό να προβλέψει την παρατηρούμενη επιτυχή και ανεπιτυχή συμπεριφορά των τεσσάρων τοίχων. / The seismic response of four reinforced soil segmental retaining walls in Taiwan, is analyzed using the dynamic finite element method. The walls – whose heights ranging from 3.20 m to 5.60 m and layers of geogrid reinforcement – were subjected to the Chi-Chi earthquake (1999) and their performance ranged from successful to unsuccessful: two of them were collapsed, one suffered only minor damage whereas the fourth wall remained practically intact. The non-linear analyses were based on the known geometrical and mechanical characteristics of each wall and of the geogrid reinforcement, the geotechnical conditions at each site and the type and properties of backfill material. The soil material behavior was modeled by using the Mohr-Coulomb failure criterion whereas recorded accelerograms in the vicinity of the sites of the walls were used as base excitation in the dynamic finite analyses. The results of the analyses (and especially the estimated deformed shape of the walls) showed a remarkable agreement with the observed performance of the walls. Based on these results the reasons for the unsuccessful performance of the two failed walls were identified whereas the differentiation of the behavior of the two undamaged walls was explained. Furthermore, parametric analyses were conducted to identify the effects of such important design parameters as the depth of the foundation of the wall, the spacing and length of reinforcement, the contribution of connecting pins to the stability of the facing elements as well as the contribution of the top layer of reinforcement to the stability of the wall. The stability of the walls were also analyzed by using a commercially available limit equilibrium software which was found to be able to predict the observed successful and unsuccessful performance of the four walls.