MODALIDADES DE INTEGRACIÓN DE EMPLEO DE LAS PERSONAS CON DISCAPACIDAD

This event is considered as the largest earthquake to ever impact Jakarta (then Batavia). However, not much information is available to analyze this event [Albini et al., 2013; Musson, 2012]. Ground shaking was felt over the whole of Java and SE Sumatra. It was felt most strongly in West Java as depicted in Fig. 3.4. Ground shaking caused 27 sheds and houses to collapse in Zandsee and Moorish gracht located in the present-day Central Jakarta where the Jakarta Cultural Centre is now standing. It was reported that ’a mighty bang’ was heard from Mount Salak two minutes after the quake and Mount Gede ’smoked’. Meanwhile, Banten suffered from strong vibrations. A weak vibration was felt in Cirebon, and a seaquake was observed by the ship Willem Frederik, which was at the entrance to the Sunda Strait [Wichmann, 1918]. Albini et al. [2013] estimated the minimum magnitude could have been Mw8.5 or larger. Three scenarios are proposed for this event as described in the succeeding paragraphs.

Scenario 1780A in Fig. 3.4arepresents a M7.0 event with a depth of 12km, located on the Baribis Thrust. This reverse fault is located on the northern part of Java and spans from Purwakarta Regency to Baribis Hills in Majalengka Regency [Bemmelen, 1949]. It has a dip angle of 31◦ to the south and a slip rate 1.5 mm/year [Hutapea & Mangape, 2009; Simandjuntak & Barber, 1996]. The Baribis-Kendeng Fault can be traced from the Sunda Strait eastwards across Java and through the Bali Basin into the Flores Thrust, north of Flores and may continue eastward up to the Wetar Thrust. This major Java back thrust is regarded as having been active since the Late Neogene [Simandjuntak & Barber, 1996]

The Baribis Fault is considered to be an active fault and is associated with a destructive earthquake in Majalengka Regency which occurred on 6 July 1990. This was a M5.5 earthquake with epicenter at 6.094◦S and 108.12◦E and focal depth of 14.2km. In the eastern part of this thrust, in the Anggarwati village, around 150 houses were damaged, 7 people were injured and 1 villager was killed [Soehaimi, 2011]. However, there has been

§3.4 DSHA of the 22 January 1780 event 45

no record of a destructive earthquake in the western part of the fault, the portion that is close to Jakarta.

In the afternoon of January 22, 1780, a weak subterranean noise was heard, which was shortly followed by a rumbling resembling a heavy-laden lorry passing by. This small shaking was followed by larger shaking that destroyed and collapsed 27 sheds and houses in central Jakarta [Wichmann, 1918]. Unfortunately, less is known about the type of building collapsed¿ However, from this information, it suggested that earthquake intensity in Jakarta was in range III MMI (resembling a heavy-laden lorry passing by) to VIII MMI (building collapsed). This scenario 1780A resulted comparable intensity in south Jakarta (VII–IX MMI). Wichmann [1918] reported similar intensity was felt in Bogor meanwhile this scenario estimate VII – VIII is likely to happen in Bogor, Cianjur and surrounding area as shown in Fig. 3.4a

Wichmann [1918] also indicated that weak shaking was felt in east coast of Java, as well as in Cirebon (approximatelly II–III MMI) while much larger vibration was felt in Banten (estimated V–VI MMI). This scenario results good intensity estimation for Banten but highly overestimated in Cirebon. It was also reported by Wichmann [1918] that ’a mighty bang’ was heard at Mt. Salak (south west of Bogor) Mt. Gede has smoked several tiems after the quake. However, it is difficult to assess whether the volcanic activities were reelated to earthquake or not.

Scenario 1780B in Fig. 3.4b is for a hypothetical crustal fault generating a M7.0 earthquake at a depth of 12km. Similar to Scenario1780A, Scenario 1780B also using GMPE proposed by Chiou & Youngs [2008] to calculate ground motion. Scenario 1780B results a good prediction of intensity in Jakarta and Bogor, slightly overestimated in Banten and and higher estimation in Cirebon. In general, Scenario 1780B produces similar ground motion distribution in comparison with Scenario 1780A. Boths scenarios produce good estimation of ground motion.

The intensities estimated for Jakarta, Bogor, Banten and Cirebon are MMI VIII, VI, IV and III respectively. Few recorded data were available to determine the intensity in Mount Gede and Mount Salak. Scenarios 1780A and 1780B resulted in a maximum inten- sity of MMI VIII in Jakarta, Bogor and Banten, which seem to be overestimates. These simulations also yielded similar intensity estimates in Cirebon, while historical accounts reported smaller intensity values.

Scenario 1780C in Fig. 3.4c refers to an intraslab M 8.0 earthquake at 160 km depth. It resulted in high intensity (VII–VIII MMI) along the north coast of West Java and part of Central Java (Tegal) which are composed of alluvium. Along the middle mountains-range, from Sunda Strait to Bogor, Cianjur, Bandung to the east, simulated MMI is about VI–VII MMI while in the southern mountains range, the simulated MMI is about IV MMI. Narrow band of VI–VII MMI is also appeared along south coast of west Java where alluvium is deposited.

As in Scenario 1780A and 1780B, this scenario also results good perdiction of MMI for Jakarta, Bogor and Banten. However, simulated MMI in Cirebon is far to high compare to intensity reported inWichmann [1918]. In addition, medium level of intensity (VI-VII) is also spreading in most of the West Java Region where information regarding the effect of the earthquake is not available.

Scenario 1780A and Scenario 1780B resulted in good prediction of ground motions for Jakarta and Bogor. However for Tegal and Banten which are situated 200 km and 80 km away from Jakarta respectively, Scenario 1780B generated estimates higher than observed. Among these scenarios, Scenario 1780A yields the most reliable estimates.

Figure 3.4: Intensity model of 22 January 1780 event resulted from scenarios Baribis thrust (a), strike-slip crustal fault (b) and intraslab (c). Middle mountains-range is lying on the central of West Java from Sunda Steet in the west to Bogor, Cianjur, Bandung and goes through to the east, is estimated to hit by ground motion with intensity about VI–VII. The green clolor in south Java is southern mountains-range where simulated MMI is about IV MMI. Black rectangles denote cities and colored circles denote estimated historical MMI, white circles denote cities where shaking was felt in unknown intensity.