Indian Ocean Tsunami Research Articles

Special Symposium, Collective Vigilantism in Global Comparative Perspective A Wave of Lynching: Morality and Authority in Post-Tsunami Aceh

Lynching is a surprisingly prevalent form of collective violence. We argue that two conditions can cause lynching: a shared morality based on salient collective threats, providing justification, and weak authority, creating opportunity. We examine this argument with the 2004 Indian Ocean tsunami. In Aceh, the province most impacted, the tsunami was a shock to morality (producing a religious revival) and authority (creating a situation of institutional flux). Using World Bank data, we find that Aceh saw an increase of lynchings, while lynchings stayed on average the same in other parts of Indonesia. Within Aceh, the increase was most pronounced where authority was most undermined and where locals had high levels of shared morality. These findings have implications for research on collective violence and the prevention of lynching.

The role of Acehnese women in enhancing community preparedness through the inter-generational transmission of local and indigenous knowledge

Intergenerational transmission of traditional knowledge plays an important role. The involvement of women shows a significant impact on building family and community preparedness. However, limited attention paid to the unique contributions of Acehnese women has identified an erosion of traditional knowledge systems in the local context. This study explores the role and involvement of Acehnese women in the intergenerational transmission of knowledge about disaster preparedness based on local wisdom. A qualitative study in Banda Aceh and Aceh Besar involving interviews with key informants namely where they live, victims or non-victims of the 2004 Aceh tsunami, and career women or housewives. Acehnese ethnic women living in coastal areas were sampled randomly and purposively. Ten agreed to participate and were interviewed. The face-to-face interviews were recorded, transcribed, and analyzed using an analytical framework. The interviews revealed that the role and involvement of women in the transmission of local knowledge and practices was hampered by cultural and political factors which caused the erosion of this knowledge.

The Collapse of the New Orde Regime Resulted in Changes in Indonesia's Economic Policy

The reform era or the post-Suharto era in Indonesia began in 1998, to be precise when President Soeharto resigned on May 21 1998 and was replaced by the then vice president, BJ Habibie . This period was founded bya more open socio-political environment. Issues during this period included the push for democracy and a stronger civilian government, elements of the military trying to maintain influence, growing Islamism in politics and society in general, and demands for greater regional autonomy . The reform process resulted in a higher degree of freedom of speech , in contrast to the widespread censorship during the New Order . As a result, political debate has become more open in the mass media and artistic expression has increased. Events that have shaped Indonesia in this period include a series of terrorist incidents (including the 2002 Bali bombings ) and the 2004 Indian Ocean earthquake and tsunami . Using the knife of deconstruction of critical legal theory and socio-legal methodology with statutory, historical, conceptual and legal political economy approaches, three questions are raised, firstly the role of law in the market reform agenda which underlies the idea of limiting the role of the state in the economy; second, how is the role of the state in the economy being debated in the MPR and; third, what are the implications of the market reform agenda for the results of changes to the economic constitution.

Lessons in personal change; how a book helped me to be an effective leader

In the aftermath of the December 2004 Asian tsunami, as the newly elected Dean of the Faculty of Medicine, University of Ruhuna, I had to face many challenges. A self-help book, titled “The 7-Habits of Highly Effective People” authored by Dr. Stephen R Covey, had a profound positive effect on my life, empowered me and helped to overcome these challenges. The unique feature of this book is that it advises on character building rather than achieving success as in most self-help books. The 7-habits that are recommended by Dr. Covey are: be proactive; begin with the end in mind; put first things first; think win-win; seek first to understand, and then to be understood; synergize; sharpen the saw. Each habit is discussed, followed by an example of project/activities for which I gave initiative and leadership.

Deformation Analysis of 2012 Mw8.6 Indian Ocean Earthquake Based on GPS Data in Preseismic, Coseismic, and Postseismic Phases

The earthquake was one of the biggest natural disasters in Sumatra and dramatically affected this region and the surrounding area. Determination of surface deformation due to the earthquake is essential for disaster mitigation. The Global Navigation Satellite System (GNSS) is a commonly used method for determining surface deformation due to earthquakes. This study analyzes surface deformation during the preseismic, coseismic, and postseismic phases due to the 2012 Mw8.6 Indian Ocean earthquake. The study used Global Positioning System (GPS) data from the Sumatran GPS Array (SuGAr) network. The most significant horizontal deformation was observed at the LEWK station, which was 280.554 mm towards the northeast and experienced a subsidence of 40.830 mm in vertical deformation. Horizontal deformation is still felt by 22.453 mm to the northeast and vertical deformation of 8.810 mm (uplift) at stations that are farther (580 km) from the earthquake's epicenter. However, in the observation period of 60 days (postseismic phase), stations closer to the epicenter are still experiencing a postseismic phase. In contrast, stations far from the epicenter show that the postseismic phase is almost complete. In the preseismic phase, all stations experience almost the same horizontal deformation, ranging from 2.210 mm-3.639 mm, but with a different direction of movement, which may be caused by previous intense earthquake activity, which is still releasing energy (postseismic phase). On the other hand, the vertical deformation during the preseismic phase generally experiences an uplift except at the LEWK station. The results of this study can be additional information for earthquake mitigation in the Sumatra region

Business grants following natural disasters and their different impact on the performance of female and male-owned microenterprises: Evidence from Sri Lanka.

This paper investigates gender differences in the treatment effects of business grants on firm performance following natural disasters, and seeks to identify the mechanisms underlying the unequal effects. A panel data-set from an experiment in Sri Lanka is used to measure the difference in the treatment effects of a business grant on the performance of female and male-owned firms following the 2004 Indian Ocean tsunami. The sample of 608 microenterprises includes 297 female-owned firms and 311 male-owned firms. There are 338 firms (Male = 176, Female = 162) in the treatment group that received the grant and 270 firms (Male = 135, Female = 135) in the control group that did not receive the grant. Data on firm performance, firm characteristics and owner characteristics were collected in 13 survey waves from April 2005 to December 2010. Firm performance, which is measured by firm profit, is assessed by employing linear regression with fixed effects in an intention-to-treat analysis. The results suggest that the business grant has a positive impact on the performance of male-owned firms, but zero effect on that of female-owned firms. Several potential mechanisms drive the results, including gender differences in business investment, household expenditure and initial business closures. The results also show a positive treatment effect of the business grant on the psychological recovery of recipients, but there is no evidence supporting gender differences in this dimension. This paper provides new evidence on gender differences in the treatment effects of business grants on firm performance in the context of post-disasters, and has implications for business recovery programs aimed at supporting female microentrepreneurs in the aftermath of large-scale catastrophes.

Factors affecting the intention to prepare for tsunami in Thailand

The threat brought by natural disasters such as tsunamis is evident since the major chaotic event happened in 2004. Related studies have dealt with the mapping and routes for efficient evacuation but limited works of literature considered the intention to prepare for tsunamis. This study aimed to analyze different factors affecting the intention to prepare for tsunamis through the integration of the Theory of Planned Behavior and Protection Motivation Theory. A total of 736 valid responses collected via convenience sampling answered a self-administered cross-sectional online survey to measure the behavioral aspects holistically. Through the use of structural equation modeling, factors such as understanding tsunami affecting perceived severity (PS) and perceived vulnerability (PV) were seen to be the most significant relationship. In addition, attitude on intention to prepare showed a significant direct relationship, which led to an understanding of tsunami having an indirect effect on intention to prepare through PS, PV, and attitude. It could be deduced that when people understand the impact, severity, vulnerability, and aftermath brought by tsunamis, individuals would have a high positive relationship to attitude to prepare for tsunamis. This study presented practical and government implications for promoting mitigation and preparedness among people for tsunami. Moreover, the findings of this study may be applied to other countries that may be affected by tsunamis. This study is considered the first study that measured intention to prepare for tsunami holistically. Lastly, this study contributes to people's intention towards preparation for natural disasters which can be applied and extended for other calamities worldwide.

Seismic source mapping by surface wave time reversal: application to the great 2004 Sumatra earthquake

SUMMARY Different approaches to map seismic rupture in space and time often lead to incoherent results for the same event. Building on earlier work by our team, we ‘time-reverse’ and ‘backpropagate’ seismic surface wave recordings to study the focusing of the time-reversed field at the seismic source. Currently used source-imaging methods relying on seismic recordings neglect the information carried by surface waves, and mostly focus on the P-wave arrival alone. Our new method combines seismic time reversal approach with a surface wave ray-tracing algorithm based on a generalized spherical-harmonic parametrization of surface wave phase velocity, accounting for azimuthal anisotropy. It is applied to surface wave signal filtered within narrow-frequency bands, so that the inherently 3-D problem of simulating surface wave propagation is separated into a suite of 2-D problems, each of relatively limited computational cost. We validate our method through a number of synthetic tests, then apply it to the great 2004 Sumatra–Andaman earthquake, characterized by the extremely large extent of the ruptured fault. Many studies have estimated its rupture characteristics from seismological data (e.g. Lomax, Ni et al., Guilbert et al., Ishii et al., Krüger & Ohrnberger, Jaffe et al.) and geodetic data (e.g. Banerjee et al., Catherine et al., Vigny et al., Hashimoto et al., Bletery et al.). Applying our technique to recordings from only 89 stations of the Global Seismographic Network (GSN) and bandpass filtering the corresponding surface wave signal around 80-to-120, 50-to-110 and 40-to-90 s, we reproduce the findings of earlier studies, including in particular the northward direction of rupture propagation, its approximate spatial extent and duration, and the locations of the areas where most energy appears to be released.

Analysis of the coseismic slip behavior for the MW = 9.1 2011 Tohoku-Oki earthquake from satellite GOCE vertical gravity gradient

Over the past decade, the three largest and most destructive earthquakes in recent history with associated tsunamis occurred: the Mw = 9.2 Sumatra-Andamam in 2004, then the Mw = 8.8 Maule in 2010, and finally the Mw = 9.1 Tohoku- Oki in 2011. Due to the technological and scientific developments achieved in recent decades, it has been possible to study and model these phenomena with unprecedented resolution and precision. In addition to the coseismic slip models, for which joint inversions of data from various sources are carried out (e.g., teleseismic data, GNSS, INSAR, and Tsunami, among others), depicting the space-time evolution of the rupture, we have high-resolution models of the degree of interseismic coupling (based on GNSS) and also maps of seismic b-value changes. Among these advances, new Earth gravity field models allow mapping densities distribution homogeneously and with a resolution (in wavelengths) of approximately the large rupture areas of great megathrust earthquakes. In this regard, the maximum resolution of GOCE-derived static models is in the order of λ/2≈66 km, while GRACE monthly solutions are in the order of λ/2≈300 km. From the study of the static and dynamic gravitational field, it has been possible to infer mass displacements associated with these events, which have been modeled and compared to the deformation inferred using other methods, yielding very good results. In this work we study the kinematic behavior of the rupture process for one of these largest events, the Mw = 9.1 Tohoku-Oki 2011 earthquake, employing the vertical gradient of gravity derived from the GOCE satellite, finding that the maximum slip occurred close to a lobe of minimum Tzz, as was observed for other case-studies in other subduction-related settings studied in previous works (e.g., the Maule earthquake and the Sumatra-Andaman earthquake, among others). In addition, from the rupture propagation using kinematic models, it can be observed that the rupture is arrested when it approaches high-density structures and, it is enhanced when connecting with lobes of low vertical gravity gradient. We also mapped a block expressed as a low Tzz lobe, developed along the marine forearc, which is controlled by a parallel-to-the-trench normal fault that accommodates subsidence during the interseismic period, as it is coupled with the subducted slab. Then, after rupturing the plate interface, this block is decoupled promoting tectonic inversion and uplift. In this way, the hypothesis that the density structure along the forearc is the ultimate first-order factor that governs the rupture process is reinforced.

Tsunami risk perception, a state-of-the-art review with a focus in the NEAM region

Large-scale coastal urban sprawl, development of tourist accommodations and industrial maritime poles have highly increased the tsunami risk to people living and/or traveling along the coasts of our planet. The disastrous tsunamis in the Indian Ocean (2004) and in the Pacific Ocean (2011), as well as a suite of other damaging events worldwide, have encouraged International Institutions, first of all UNESCO Intergovernmental Oceanographic Commission, National Governments and Local Communities to implement Tsunami Warning Systems (TWS), to raise awareness on tsunami risk, and to create a multilevel risk governance. In this framework, research on tsunami risk perception plays a key role. The results of these studies should be taken into account in designing risk mitigation programs and tools (such as drills, activities with local communities, emergency plans, etc.). This paper presents a review of such studies, carried out in several countries worldwide through many thousands of interviews performed with different techniques. Most tsunami risk perception studies were carried out in the regions where the Indian Ocean Tsunami Warning System and the Pacific Ocean one (PTWS) operate. In the NEAMTWS (North-East Atlantic, Mediterranean and connected seas Tsunami Warning Systems) region, only few specific studies were conducted, mostly within the EU-funded ASTARTE project (2013–2017) and more recently in a few extensive surveys on tsunami risk perception conducted in Italy between 2019 and 2021. Although the twenty-three studies analyzed in our review show a strong heterogeneity of methodological approaches and population samples, they allow us to outline some general considerations on tsunami risk as perceived by people in the different regions of the world. With the help of a table, we schematically summarized the emerging strengths, weaknesses and lessons learned in the twenty-three papers, noting an increase in the number of such studies in the last 5 years. The surveys were mostly concentrated in high-risk areas and focused on local residents. Some differences emerged depending on the memory of past tsunamis, education level, and local cultures. This provides useful hints for sound citizen-based tsunami risk reduction actions, including improved risk communication aimed at increasing the resilience of tsunami-prone populations. The need for increasing the assessment of tourists’ tsunami risk perception, and for a more homogeneous survey strategy also emerge from our analysis.

Tsunami preparedness within Sri Lanka's education system

Asked what hazard posed the greatest threat to their school, the principals of coastal schools in the Galle, Ampara and Batticaloa districts of Sri Lanka overwhelmingly responded “tsunami”. This result is unsurprising considering the scale and trauma caused by the December 26, 2004 Indian Ocean tsunami. This tsunami claimed over 35,000 victims in Sri Lanka, a third of whom were children. It damaged and destroyed 182 schools, and a further 287 served as camps for internally displaced persons. Given that Sri Lanka is far from all potential sources of earthquake-induced tsunami, and that there is time for early warning and evacuation, it is crucial that coastal schools are prepared and ready to act. This study uses semi-structured interviews with school principals and regional education and disaster management officials to gain insights into the tsunami preparedness of the Sri Lankan education sector. Overall, our findings show that schools are heavily reliant on tsunami early warning towers for their warning, yet only half of the 430 Sri Lankan schools exposed to tsunami are within audible range of a tsunami early warning tower. It is crucial therefore that alternative and backup early warning channels are established where needed. However, the interviews show that there is a very low level of baseline hazard preparedness. There are few or no fire drills, let alone tsunami evacuation plans or drills. The school principals express the view clearly that the education system in Sri Lanka is ill-prepared for a future tsunami. We find however that there are opportunities to involve existing safety committees in school preparedness and in the development of evacuation plans; and to exploit existing regular teacher curriculum training events to develop capacities in emergency response and evacuation. Importantly, experiences from a past tsunami drill with Sri Lankan communities emphasise the importance of holding regular school practice drills as well as “end-to-end” (from tsunami detection to tsunami evacuation) community evacuation exercises.

Application of the PTVA–4 Modeling in Assessment of Building Vulnerability to Earthquake and Tsunami: A Simple and Reliable Method for Preliminary Study of Tsunami-Prone Zones

The earthquake and tsunami in Aceh Province, Indonesia, in 2004 caused the deaths of nearly 200,000 people and an economic loss of up to USD 4 billion. The recurrence period for the tsunami in Aceh is 250-400 years. Along the subduction zone between the Eurasia continental plate and the Indo-Australia oceanic plate, the southern region of Java Island is a vulnerable zone whose recurrence period is not known until nowadays. This zone is a densely populated area and the largest source of Indonesian economic income besides the north coast of Java. Therefore, a building vulnerability study is needed to minimize casualties and financial losses. The PTVA–4 modeling is a suitable method to be developed because it is reliable and does not require high costs. We conclude that this method is accurate by assessing the modelling results on the impact of the 2006 earthquake and tsunami in Cilacap, Indonesia.

Financial market responses to a natural disaster: Evidence from credit networks and the Indian Ocean tsunami

We examine changes in financial allocations in Rotating Savings and Credit Associations (Roscas), a popular group-based financial institution world-wide, in the aftermath of the 2004 Indian Ocean tsunami. With financial data from locations along the South Indian coast we estimate the causal effect of this major natural disaster on financial flows between occupational groups, the price of credit and other loan characteristics. We find that the supply of funds in these credit networks remained remarkably stable, while demand by small and medium-scale entrepreneurs increased significantly. In response, substantial funds were channeled from wage-employed members and commercial investors to entrepreneurs. We conclude that natural disasters affect individuals with substantial heterogeneity and that the Roscas we study offer more scope for gains from trade in response to a seemingly aggregate shock than commonly assumed for traditional credit and insurance networks.

Tsunami Resettlement Program and Survivor Satisfaction Fifteen Years After the 2004 Tsunami in Aceh, Indonesia

Fifteen years after the Aceh tsunami, the housing for the tsunami survivors has undergone material changes and shifts in ownership. This study analyzed the survivors’ satisfaction with the housing aid and examined the decision-making mechanisms that occurred during the rehabilitation-reconstruction period for housing construction in the relocation and non-relocation areas. This study used qualitative-descriptive methods. Interviews and focus group discussions were used to collect the data and respondents were selected by purposive sampling. The findings indicated that the decision-making in the relocation and non-relocation areas for housing reconstruction was partially top-down. There were four aspects of this decision-making: (1) choice of location; (2) quality and materials of the house; (3) house construction; and (4) supervision of house construction. However, the survivors in both the relocation and non-relocation areas were only involved in the house construction and supervision of house construction elements. The survivors’ satisfaction criteria differed between those in the relocation vs. non-relocation areas. The satisfaction of survivors in the relocation areas was based on the distance and quality of the houses and access to public facilities. For the non-relocation area survivors, house quality was the only significant factor.
 Keywords: life satisfaction, survivors’ satisfaction, housing, relocation, decision-making

Longitudinal outcomes of post-traumatic stress disorder among the Indian Ocean tsunami survivors in Indonesia

Post-traumatic stress disorder (PTSD) following a disaster could change over time. This study aimed to analyze the risk factors of PTSD among the 2004 Indian tsunami survivors in Aceh and North Sumatra province, Indonesia. It mapped the trajectory recovery pattern of mental illness and examined the medium-term PTSD consequence five and 18 months after the disaster using a large longitudinal survey. Multivariate logistic regression was employed to derive the association between the post-traumatic stress disorder trajectory group and risk factors. The results showed that 15% and 20% of the respondents had persistent medium-term and delayed-onset PTSD, respectively. The vital predictors of persistent PTSD included being female, aged 50 and older, married, and having higher direct trauma exposures to the tsunami. Furthermore, delayed-onset PTSD was associated with negative life events after the tsunami and perceived less social support. The results indicate the necessity to understand the predictors for each PTSD trajectory group's effective intervention regarding mental health after the disaster.

Android Real Time Earthquake & Tsunami Warning Alert System Based on Open Data of Indonesia Government Agency of Geophysics

There are approximately 4000 earthquakes happened in Indonesia per year, whereas earthquakes of a magnitude greater than 5.5, or earthquakes that can be physically felt on land, average around 70-100 per year, and destructive earthquakes around one to two times a year. Not all earthquakes cause tsunamis, but the majority of tsunamis are caused by earthquakes. Since the earth was formed, a number of tsunamis have been happening all over the world. The Aceh tsunami is one of the biggest tsunami history over past 2 decades which occurred on 26 December 2004, claimed the lives of around a quarter of a million people in areas surrounding the Indian Ocean. The very short tsunami arrival time of 10 – 60 minutes is a challenge for tsunami early warning. It also has a direct impact on evacuation procedures and means that evacuation times are very short as well. The objective of this study is to develop android real time earthquake & tsunami alarm as early warning system, evacuation directions and earthquake survivor detection for rescuer to reducing disaster risk. This study used the Research and Development method with the ADDIE (Analyze, Design, Development, Implementation and Evaluate) procedure. The result of this study the apps obtained less than 5 seconds respond time to proceed the earthquake & tsunami information from BMKG website to trigger early alarm in users android mobile phone. Android alert system more effective because it has a lower response time (< 5 seconds) than previous early warning system with a longer response time (13.48 seconds). In additions, developers improve the system not only distribute earthquake and tsunami information, but also provide evacuation route direction & survivor detection as a disaster risk reduction. Although in actual, this feature has the potential to be disrupted due to the large amount of user traffic. So it requires a large number of server resources if there are many active users.

The Chicxulub Impact Produced a Powerful Global Tsunami

AbstractThe Chicxulub crater is the site of an asteroid impact linked with the Cretaceous‐Paleogene (K‐Pg) mass extinction at ∼66 Ma. This asteroid struck in shallow water and caused a large tsunami. Here we present the first global simulation of the Chicxulub impact tsunami from initial contact of the projectile to global propagation. We use a hydrocode to model the displacement of water, sediment, and crust over the first 10 min, and a shallow‐water ocean model from that point onwards. The impact tsunami was up to 30,000 times more energetic than the 26 December 2004 Indian Ocean tsunami, one of the largest tsunamis in the modern record. Flow velocities exceeded 20 cm/s along shorelines worldwide, as well as in open‐ocean regions in the North Atlantic, equatorial South Atlantic, southern Pacific and the Central American Seaway, and therefore likely scoured the seafloor and disturbed sediments over 10,000 km from the impact origin. The distribution of erosion and hiatuses in the uppermost Cretaceous marine sediments are consistent with model results.

Finite Element Modeling of Tsunami-induced Water Levels and Associated Inundation Extent: A Case Study of the 26th December 2004 Indian Ocean Tsunami

Abstract In recorded history, the tsunami due to the Great Sumatra earthquake of 26th December 2004 has been the most devastating, causing the loss of over 230,000 lives besides extensive damage to most of the coastal provinces bordering the Indian Ocean. Real-time prediction of tsunami wave heights and resultant inundation of inland coastal areas are essential to safeguard the life and property of the coastal community. In the present work, a finite-element-based ADvanced CIRCulation (ADCIRC) model (widely used for storm surge simulations) is used to compute tsunami wave height and associated coastal inundation due to the 2004 event. The prime focus is on the Cuddalore coast along the east coast of India, which was heavily affected due to the tsunami. A grid resolution of around 50 m was used in the Cuddalore region to simulate the inundation in the area. Computed results are validated against the available observations. It is noticed that the model computations are in good agreement with the observations. Simulation results depict that because of its computational efficiency and accuracy, the ADCIRC can be used for near real-time prediction across the tsunami warning centers.

„Mindent eláraszt, ami az útjába kerül” – a 2004-es indiai-óceáni földrengés és szökőár katasztrófadiplomáciai elemzése

The 2004 Indian Ocean earthquake and tsunami was the result of a highly complex process that involved the release of enormous amounts of seismic energy. Although the magnitude of neither the earthquake nor the tsunami was unprecedented, due to the size of the affected area, the height above sea level, the size and density of the local population, as well as the unpreparedness of the risk management, the disaster can be identified as the most destructive catastrophe of humanity. The present research examines the events of the 2004 tsunami in the context of Southeast Asian disaster diplomacy. The methodological framework of the study is the complex adaptive system (CAS) method, which is applied in the analysis of complex adaptive systems through four properties and three mechanisms. Among the variables of the CAS method, the property of diversity as well as the mechanism of building blocks determined regional cooperation. The natural disaster of 2004 demonstrates well that the member states of the Association of Southeast Nations are capable of disaster cooperation despite the unsuccessful protection measures.

Fingerprinting sources of beach sands by grain-size, using mid-infrared spectroscopy (MIRS) and portable XRF. Implications for coastal recovery along a tsunami-struck delta coastline

Determining modern sediment provenance along sandy beaches helps understanding coastline dynamics and can therefore assist coastal management. Provenance analysis relies usually on mineralogical, elemental, and isotopic fingerprinting of sediment sources. Mid-Infrared Spectroscopy (MIRS) offers a rapid and non-destructive alternative. It relies on the identification of molecular-bonds in organic and inorganic materials. Thus far, MIRS has been used to fingerprint fine-grained sediments in mountainous and agricultural catchments. Here we use MIRS to analyze a range of sediment grain sizes (<0.25 mm; 0.25–0.5 mm; 0.5–2 mm) in modern fluvial and coastal sands, located in the delta of the Aceh River in Sumatra. Variations in molecular bond associations are compared to variations in major element concentration, quantified by portable X-ray fluorescence (pXRF) on a subset of samples. Covariations between MIRS and pXRF data are used to predict major element concentrations in all samples. Discriminant Analysis (DA) is used to classify sand-feeding streams into groups possessing distinctive MIRS fingerprints. DA proximity relationships are then used to predict the contribution of each source group to trunk stream sand and beach sands. The best discrimination is obtained among sands belonging to the medium grain-size fraction. Simple forward modeling of the expected contributions of the different sources is used to shade light on the DA-predicted association patterns. It helps discussing the biases introduced by sediment compositional changes from the headwaters to the coast, especially hydrodynamic sorting. We find that sand composition along the delta shoreline is primarily controlled by the asymmetric dispersal of sediment from the Aceh River mouth, owing to directional longshore drift. Local variations are generated by particle-size effects and by the propensity of the coast to erode or thicken over the past century. The coastal stretches the most severely damaged by the 2004 Indian Ocean Tsunami exhibit the greatest variations in apparent provenance between sub-fractions.