LOCAL SITE ANALYSIS BY MICROTREMOR AND ITS RELATIONSHIPS TO REGIONAL PLANNING (A LESSON LEARNED FROM BANTUL, JETIS, IMOGIRI AND KRETEK SUB-DISTRICTS) By :
Arif Gunawan & Parfi Khadiyanta
Outlines Introduction Brief Methodology of The Research Main Expected Results of The Study The Conclusion
INTRODUCTION
GENERAL VIEW
• Coverage Area of Bantul Regency: 506,85 km2 • Administratively it consist of 17 sub-districts, 75 villages and 933 pedukuhan (dusun).
ANALYSIS OF LOCAL SITE EFFECTS OF BANTUL EARTHQUAKE:
• Local site effects is one of the natural phenomena due to seismic waves’s effect which vary in each site (Bath, 1979). • It caused by configuration of geological conditions in which composed on it as well as landforms distribution at the site. • In Bantul where its viewed as morfo-structure and formed as “graben”, while either the amplification or de-amplification of seismic waves propagates through unconsolidated as well as solid materials.
THE 3-D* ‘GRABEN/BASIN BANTUL’
Merapi Mt. Kulon Progo Mts.
Southern Mts.
Yogyakarta City ‘Graben /Basin Bantul’
*) compiled by global mapper and google earth **) Rahardjo et al, 1995 in Mulyaningsih et al, 2006
LAND SLOPE’S CHARACTERISTICS: No
1
Wilayah Kecamatan
Kecamatan Bantul
Parameter Penelitian Persen Lereng (%)* 0-8 %
Luas
Keterangan
(ha) 2.195 ha
2
Kecamatan Jetis
0-8 %
2.300 ha
8-15%
147 ha
3
4
Kecamatan Imogiri
Kecamatan Kretek
0-8 %
248 ha
8-15%
5.201 ha
0-8 %
2.302 ha
8-15%
375 ha
Courtesy of Analytical Results (2011) and Bappeda of Bantul (2010) * van Zuidam (1983)
Bentang alam berupa dataran dengan relief landai Proses sedimentasi dan erosi relatif seimbang dan tidak terlalu intensif Bentang alam didominasi dataran berelief landai, hanya di sebelah timur merupakan dataran dgn relief agak curam Proses erosi intensif di bagian timur; sedimentasi terjadi di sepanjang DAS Opak-Oyo Bentang alam didominasi dataran berelief agak curamcuram Proses erosi terjadi intensif Bentang alam didominasi dataran berelief landai kecuali di sebelah timurtenggara yang curam reliefnya (berbatasan dgn kec Pundong) Selain di bagian timurtenggara terjadi sedimentasi di muara S. Opak hingga sepanjang S. Opak. Di timur-tenggara erosi intensif terkait lereng yg curam
TOPOGRAPHY-GEOMORPHOLOGY-LANDFORMS: No.
Wilayah
Parameter Penelitian*) Kerapatan kontur: jarang Bentuk lereng : planar (plain) Elevasi (m): 0-125 Kerapatan-kontur: dominan-berkontur jarang Bentuk-lereng: didominasi-planar (plain) Elevasi (m): dominan antara 0-125; sebagian kecil luas lahan di timur 125-375
Kelas Geomorfologi** Dataran dengan berelief halus
Bentuk Lahan***) Fluvio volcanic dan Kaki vulkanik Merapi Didominasi oleh Fluvio volcanic Sebagian kecil (bagian timur) merupakan Pegunungan Selatan (Southern Mountainous)
1
Kecamatan Bantul
2
Kecamatan Jetis
3
Kecamatan Imogiri
Kerapatan-kontur: dominan rapat Bentuk lereng: dominan cembung planar(convex plain) Elevasi (m): dominan 125-375 dan 375-500; sebagian kecil 0-125
Dataran dengan relief agak kasar hingga kasar mendominasi
Didominasi oleh Southern Mountainous yg tdr dr: kaki lereng koluvial Btragung, perbukitan str Fm NglanggranSemilir dan Fm Wonosari
4
Kecamatan Kretek
Kerapatan kontur: mayoritas kontur jarang kecuali di bagian timurtenggara yang berkontur rapat Bentuk lereng: dominan planar Elevasi (m): dominan 0-125, sedangkan di timur-tenggara 125-375
Didominasi dataran dengan relief halus. Sedangkan di timur-tenggara merupakan dataran berelief agak kasar
Didominasi oleh bentuk lahan fluvial marine dan kompleks gumuk pasir dan sedikit fluvio volcanic
Didominasi dataran dengan lereng landai; sebagian kecil merupakan dataran berelief agak kasar
Courtesy of Analytical Result (2011) from field observation as well as DEM‘s analysis *) **) based on DEM‘s analysis and Topography map @ sub-district (1:10.000) ***) based on field observation and Daryono (2011)
CHARACTERISTIC OF GEOLOGICAL CONTROL- ROCKS/SOILS: No.
Wilayah
Deskripsi Litologi
Luas (ha) 2.195
Keterangan
1
Kecamatan Bantul
Endapan sedimentasi hasil aktivitas vulkanik Gunungapi Merapi muda (Holocene). Endapan ini yang mengisi cekungan Yogyakarta yang berbentuk graben (Rahardjo et.al,1995 dan Setiadji et.al, 2008)
2
Kecamatan Jetis
2.447
3
Kecamatan Imogiri
Endapan sedimentasi hasil Gunungapi Merapi muda (dominan) dan endapan Formasi Semilir yang terdiri dari perselingan batupasir tufaan dan breksi lapili (Tertier). Sesuai menurut Mulyaningsih et al (2006) dan Setiadji et al (2008) Formasi Semilir dan Nglanggran berumur Tersier (terdiri dari perselingan batupasir tufaan-breksi lapili dan breksi andesit). Kedua Formasi ini yang menjadi penyusun Pegunungan Selatan (Mulyaningsih et.al, 2006)
5.449
Relief permukaan agak curam hingga curam. Hal ini merupakan ciri khas dari peralihan dari dataran landai (dengan litologi endapan Merapi muda) dan Pegunungan Selatan. Keterdapatan kedua formasi batuan ini ditemukan di Kecamatan Imogiri dengan ketebalan hingga 30 m
4
Kecamatan Kretek
Endapan hasil aktivitas Pegunungan Selatan dari Formasi Nglanggran (Mulyaningsih et al,
2.677
Ketebalan Formasi Nglanggran hingga mencapai 10 m
Courtesy of field observation (2011) and any other literatures
Relatif di permukaan tidak ditemukan keterdapatan struktur geologi yang menonjol. Hanya di sepanjang S.Opak yang diperoleh: perlapisan setempat yang tersingkap yakni perselingan seperti: batulempung-batupasir tufaan dengan rata-rata hingga ketebalan 50 m Keterdapatan perlapisan yang selaras antara endapan sedimen hasil Gunungapi Merapi dan endapan Formasi Semilir serta Nglanggran dengan ketebalan hingga 15 m
BRIEF METHODOLOGY OF RESEARCH
• Reviewing Landforms aspects and Microtremor within Spatial Planning Process Objectives
1. To identify and to analyze landforms characteristic by microtremor map and microtremor parametric distribution table per unit of landforms. Targets 2.To assess land use planning in the study area.
1. Frequency (fo); Amplitude H/V Spectra (A); and Seismic Vulnerable Index (Kg).
Outcomes
2. Analysis of Earthquake Hazard Risks based on Kg. 3. Supporting Microtremor for Spatial Planning in the Study Area.
Research Methodology Data Collecting Methods
Quantitative Approaches Analytical Technic 1. Descriptive-Quantitative & Comparative Spatial
Data Primary Field Observations Microtremor Measurements
Data Secondary Collecting of Data, Literatures and Documents
Information
Distribution of fo-A-Kg parameters in study area Comparison of mean Kg into the collapse ratio Comparison of land use before and after EQ 2006 Comparison of landforms in each of microtremor characteristic 2. Inferential Statistics Linear regression (due to Vulnerability Index to Collapse Ratio)
Analytical Data Processing Analytical Frameworks of the Study
1
Research Analytical Process
2
Tools (1) 1 Portable Digital Seismograph Type TDS-303 (with 3 censor components) by sampling frequency of 100 Hz, data cables, digitizer, solar cell panel, GPS, UPS, laptop (for data acquisition), digital camera. (2) Software DATAPRO for data acquisition of microtremor and in order to change data format RSHEED to data format SAF. (3) Software SESARRAY-GEOPSY for HVSR analytical. (4) Software ArcGIS dan SURVER 8 for finalizing spatial data (incl. end user interactives);
(5) Windows OS for compiling and processing data.
Microtremor tools
Courtesy of BMKG
SCHEMATIC PROCESS ANALYSIS TopographyGeomorphology (Landforms)Geology;
Microtremor measurements
I
N
Analysis of Characteristic of Landforms as well as Seismic Vulnerability Index (Kg)
PRO
Updating of information for vulnerability potential and geohazard risk
Existing Condition of Land Use
P
Analysis of Land Use before and After Disaster in the year 2006
OUT
U
Regulation and Spatial Planning Policy; Spatial Planning Act 26/2007; Disaster Control Act 24/2007
CESS
Updating information and Optimalization of Land Use in EQ Disaster Prone Area
PUT
Analysis of New-Spatial Planning Policy based on Mitigation
T
Analysis of Spatial Planning Policy
Renew of Policy and Spatial Plan yang and Adapt due to Hazard Threatness
Conclusions
Recommendations
• One of the scientific approaches for earthquake chr. microtremor. • There is the low vibration that caused the low amplitude (micrometer) and its vibrated waves on surfaces. This is because of human activities/ atmospheric disturbing ( “noise”) Motamed et al,2007; Petermans et al, 2006 in Daryono, 2009. • This research was based on horizontal to vertical spectral ratio (HVSR) Nakamura’s methods • Analysis of soil vibration within time function turn into 3 graphical recording Fourier vertical, horizontal (western-eastern), & horizontal (northern-southern)
• Each of the those spectra, then was being calculated on the mean by quadratic root means and divided into vertical component in specific frequency therefore we can conclude the mean of values of H/V spectra (Nakamura, 1989 in Daryono, 2009).
PROSEDUR OF DATA PROCESSING & ANALYSIS OF ‘HVSR’ (GEOPSY) WINDOWING
Fourier’s Transformation and Joining of Horizontal-Vertical Components
Spectrum Amplitude of H/V (A)
Resonance of Frequency (f0)
Location of Microtremor Measurements
MAIN EXPECTED RESULTS OF THE STUDY
Resonance Frequency (fo) • • • • • •
Values of resonance freq between 0,65 Hz- 13,30 Hz. In Bantul area : 0,65 Hz- 11,24 Hz In Jetis area: 1,43 Hz- 13,30 Hz In Imogiri area: 2,30 Hz- 11,24 Hz In Kretek area: 0,68 Hz- 10,46 Hz The small freq associated with landform of fluvio volcanic; dominated by Young Merapi (Quarterholocene); distributed in the middle of graben/basin • The huge freq associated with landform of structural hills (The Southern Mts -Tersier) • fo have the role of material planning and building construction fo building ≈ fo soil/seismic (?)
The Peak of Spectra Ratio Curves of H/V (A) • There is a pattern of curve peak of seismic waves the cyles of microtremor propagation through sediments. • In Bantul,Jetis and Imogiri (western areas) the amplitude: 1,62-5,1. While in Kretek: 2,17-5,86. Distributed into fluvio-volcanic and fluvio-marine. • Dominated by unconsolidated materials which symbolized with amplitudo spectra above 2,0 in contrast in the eastern (dominated by sediments in structural hills).
MAP OF MICROTREMOR PARAMETRICS (RESONANCE FREQ; AMPLITUDE AND VULNERABLE INDEX)
MAP OF LANDFORMS CHARACTERISTIC (GRABEN OF BANTUL)
Seismic Vulnerable Index (Kg)
Kg = A 2 / fo • Values of Kg in study area is around 0,29 to 35,4 divided by 3 groups: • The First Group classified as the top seismic vulnerable index : – In fluvio-volcanic its reached values of 0,47-35,4 – Map of Kg showed that the highest interpolation pattern lie on northern of Kretek regency which directly connected into Bambanglipro and Pundong regency (Kg ≈ 25,19-35,4) – The fluvio-marine and the complex of sand dunes are reaching of Kg ≈ 8,55-14,1 (high points) – Whereas Bantul, Jetis & western of Imogiri Kg > 5,0 (high points).
(continued) • The second of Kg medium seismic vulnerable index distributed into: Landform of colluvial foot-cliff on Baturagung (eastern of Imogiri). • The third low seismic vulnerable index and distributed into: Landform of structural hills that is part of the Southern Mts (Nglanggran Formation and solutional hills of Wonosari/Wonosari Fm.). Values of Kg lying on 0,45-3,31 (below of 3,5 ≈ standard empirical).
GRAPHS OF RELATIONSHIP MEAN OF SEISMIC VULNERABILITY INDEX (Kg)-LANDFORMS UNIT
1
2
3
5
Nilai Indeks Kerentanan (Kg)
4
Grafik Hubungan Rerata Indeks Kerentanan Seismik dan Satuan Bentuk Lahan 16.00
14.00 12.00 10.00 Grafik Hubungan Rerata Indeks Kerentanan Seismik dan Satuan Bentuk Lahan
8.00 6.00 4.00 2.00 0.00 1
2
3
4
Satuan Bentuk Lahan (landforms)
5
ANALYSIS OF “EQ” VULNERABILITY BASED UPON LANDFORMS AND GEOLOGY
• Each of characteristic of geophysics parametric i.e. microtremor waves (fo,A and Kg) regarding of implementation in order to support detailed spatial planning as well as to update data & information of recent disaster (PW Ministry decree 21/PRT/M/2007). • Classification of vulnerable seismic (ground shaking & ground failure) which classify as 2 types of region vulnerable area and un-vulnerable area; it relies on circumstances of landform and sediment/geological material on site.
MAP OF VULNERABILITY BASED ON PARAMETRICS MICROTREMOR
• The Vulnerable Area (≈ colour of red): – – – –
Fluvio-volcanic of Young Merapi The Foot-Cliff of colluvial Baturagung-Hills Fluvio-marine Complex of sand dunes (very specific site)
Type of Unconsolidated Sediments (Quarterly)
• The Un-Vulnerable Area (≈ colour of green): – The hills of structural of Nglanggran Fm. – The solutional hills of Wonosari Fm. Str.
Type of Consolidated Sediments (Tertiary)
Kenampakan satuan bentuk lahan Dataran Fluviovulkanik Merapi Muda
Kenampakan satuan bentuk lahan Dataran Kaki Lereng Koluvial Perbukitan Baturagung
Kenampakan satuan bentuk lahan Perbukitan Struktural Formasi Nglanggran
Kenampakan satuan bentuk lahan Dataran Kompleks Beting Gesik dan Gumuk Pasir
Kenampakan satuan bentuk lahan Dataran Fluvio marine
Kenampakan satuan bentuk lahan Perbukitan Solusional Struktural Formasi Wonosari
ANALYSIS OF “EQ” HAZARD RISK BASED ON SEISMIC VULNERABLE INDEX
• Empirical Data showed us that there is an increasingly vulnerable indexes ≈ stepping up of collapse ratio (buildings) in affected seismic area • Law of Regulations: policy analysis of spatial planning in study area (UU 26/2007;Perda 4/2011 and RDTRK) • We can define that first of bench mark in order to figure out of level of “EQ” risks has been represented into values of Kg which point out of severe destroying forces upon construction in study area
MAP OF HAZARD RISK BASED ON SEISMIC VULNERABLE INDEX
CONCLUSIONS • The study area is clearly prone region which contains vulnerable potential as well as hazard and risks by earthquake disaster in any levels. The level of vulnerability in one site had been influenced by compotition of sedimentary on site in which it connected to their unique landforms unit. Had the vulnerable index raised, therefore level of hazard risks would be increasing because of increasingly collapse ratio. • Transformation of landform characteristic and geological constelation of sub-surfaces in seismic prone area would be followed by conversion on each of its microtremor parametric significantly. These facts concluded us that the phenomena of local site effects could describe the mechanism of earthquake disaster in the past as well as contained to repeated in the future.
• To be required specific mechanism of spatial planning in the seismic prone area by limiting development of built environments that influenced by the ground shaking as well as ground failure; such as settlements, industry, trade-services which they need some kind of friendly and also hazard response material construction RTRW of Bantul Regency year of 2010-2030 (Perda 4/2011) • Map of vulnerable and map of risk are representing maps of landforms transformation as well as geological condition (sediment of rock on site) and also correlated to collapse ratio of building in the study area.
THANK YOU
FOR YOUR KINDNESS
